Steps to achieve a secure Azure migration: A UK business guide

Moving your infrastructure to Azure is one of the biggest technology decisions a UK business will make this year. Done well, it cuts cost, improves resilience and gives your teams tools they couldn't run on-premise. Done without a security plan, it opens a window of exposure that attackers are increasingly quick to find.

This guide covers the Azure migration security best practices a secure move actually depends on: the risks to plan for, the shared responsibility model most breaches trace back to, the security controls to put in place before you move a single workload, and how Microsoft Defender for Cloud fits into the process. It closes with a step-by-step checklist and answers to the questions IT and security teams ask most often about secure cloud migration in the UK.

Why Azure migration security matters in 2026

Azure cloud migration security risks are highest during the migration window itself, when your data is most exposed. Systems are in flux, permissions are being recreated, and legacy and new environments often run side by side for weeks or months. Any one of those states can hide a misconfiguration that goes unnoticed until it's exploited.

The scale of the threat backs this up. According to the UK government's Cyber Security Breaches Survey 2025/2026, 43% of UK businesses, roughly 612,000 organisations, identified a cyber security breach or attack in the past 12 months. The same survey found that only 25% of businesses have a formal incident response plan, a figure that drops to 21% among micro businesses and rises to 76% among large ones. Just 31% of businesses have a board member with explicit responsibility for cyber security.

Put together, these figures describe a lot of organisations moving critical systems to the cloud without a tested plan for what happens if something goes wrong. Security has to be designed into a migration from the outset. Retrofitting it afterwards, once workloads are live and data is already flowing, is far harder and far more expensive.

Understanding the Azure shared responsibility model

Most migration security gaps trace back to one misunderstanding: which party is actually responsible for a given control.

Microsoft secures the physical infrastructure that underpins Azure: the data centres, the physical network, and the host operating system and hypervisor. What you remain responsible for depends on the service model you choose:

Service model	What Microsoft manages	What you manage
Infrastructure as a Service (IaaS)	Physical hosts, network, virtualisation	Operating system, network controls, applications, identities and data
Platform as a Service (PaaS)	Physical hosts, network, virtualisation, operating system	Applications, identities and data, access configuration
Software as a Service (SaaS)	Physical hosts, network, virtualisation, operating system, application	Data, identities, access and how users are provisioned

As you move from IaaS towards SaaS, Microsoft takes on more of the stack, but your organisation is never off the hook for identity, access and data. Full detail is available in Microsoft's own shared responsibility documentation.

Assuming Microsoft ‘handles security’ because the workload now sits in Azure is one of the most common causes of exposure during and after a migration. The UK's National Cyber Security Centre (NCSC) publishes 14 Cloud Security Principles that give a practical, UK-specific benchmark for what good looks like, covering everything from data in transit protection to secure use of the service by your own staff. Use it to check that your migration plan actually covers the controls you're responsible for, rather than the ones Microsoft already handles.

Key security considerations before you migrate to Azure

Before any workload moves, assess your current security posture properly. The point is to find the high-priority issues while they're still on paper, not partway through a migration when a fix means downtime.

Area	Key action
Current inventory	Catalogue assets, applications and data; retire what's legacy rather than migrating it
Data security	Encrypt at rest and in transit; use UK South/UK West for residency; keep secrets in Key Vault
Network security	Map firewalls and access protocols onto Azure controls; use Private Link/Service Endpoints and ExpressRoute for sensitive workloads
Identity and access management	RBAC, least privilege, MFA, Conditional Access and Microsoft Entra Permissions Management
Incident response planning	Build and test a plan before migrating; only 25% of UK businesses currently have one
Compliance and cloud considerations	Map UK GDPR and Cyber Essentials to Azure controls; track alignment via the Regulatory Compliance Dashboard

Current inventory

Not everything needs to migrate. This is also the point to decide what's genuinely business-critical and what's legacy or redundant enough to retire rather than lift into Azure.

Data security

Classify data properly and think about residency: UK South and UK West regions exist specifically to keep GDPR-sensitive workloads within the UK. Keep secrets and keys in Azure Key Vault rather than embedded in configuration files, a mistake that shows up repeatedly in post-incident reviews.

Network security

Map your existing firewalls, intrusion detection and access protocols onto Azure's own controls. For sensitive workloads, Private Link or Service Endpoints combined with a VPN Gateway or ExpressRoute connection keep traffic off the public internet entirely.

Identity and access management

Role-based access control (RBAC) and least-privilege principles should apply from day one. Multi-factor authentication and Conditional Access policies should be non-negotiable for any account with elevated access. If you're operating across multiple clouds or a hybrid environment, Microsoft Entra Permissions Management gives you visibility into who can access what, across all of it.

Incident response planning

Decide who's responsible, how you communicate internally and externally, and what recovery looks like, before you migrate rather than during an incident. This is one of the cheapest gaps to close ahead of time.

Compliance and cloud considerations

Map any sector-specific regulation onto the Azure controls that satisfy it. Microsoft Defender for Cloud's Regulatory Compliance Dashboard is a practical way to track alignment against these frameworks over time, rather than treating compliance as a one-off audit exercise.

Leveraging Microsoft Defender for Cloud

Microsoft Defender for Cloud is a cloud-native application protection platform, usually shortened to CNAPP: a single platform that brings together the different disciplines of cloud security rather than requiring separate tools for each. It's built around three pillars:

• DevSecOps, which brings security into the development pipeline at code level, so vulnerabilities are caught before deployment rather than after.
• Cloud Security Posture Management (CSPM), which continuously assesses your environment and highlights the specific steps that would reduce your risk of a breach.
• Cloud Workload Protection Platform (CWPP), which protects the workloads themselves, including virtual machines, containers, storage and databases, once they're running.

For a migration specifically, Defender for Cloud is useful at three distinct points: assessing your security posture before you move anything, monitoring workloads as they transition (when configurations are most likely to be incomplete), and providing continuous protection once everything is live in Azure.

Key features and benefits of Microsoft Defender for Cloud

• Unified security management across hybrid and multi-cloud environments, so you're not managing security separately for on-premise, Azure and any other cloud platform in use.
• AI-powered threat protection that identifies malware, ransomware and zero-day attacks based on behaviour, not just known signatures.
• Vulnerability management that gives prioritised, actionable recommendations rather than a long undifferentiated list of findings.
• Compliance tracking, including integration with Microsoft Purview for data governance and regulatory mapping.
• Secure Score, a single benchmark you can use to track whether your security posture is actually improving month on month, and to justify further investment to the board.

A step-by-step checklist for a secure Azure migration

Step	What to do
1. Assess	Catalogue assets, applications and data; identify what's business-critical and what can be retired
2. Classify	Classify data by sensitivity and confirm residency requirements (for example UK South/UK West)
3. Configure identity	Set up RBAC, least-privilege access, MFA and Conditional Access before migrating any workload
4. Configure network	Apply firewalls, Private Link/Service Endpoints and secure connectivity (VPN Gateway/ExpressRoute)
5. Enable Defender for Cloud	Turn on posture assessment ahead of migration, not after
6. Test	Run a pilot migration for a low-risk workload before moving critical systems
7. Migrate	Move workloads in planned phases, verifying security configuration at each stage
8. Monitor	Maintain continuous monitoring and review Secure Score after go-live

Common Azure migration security mistakes to avoid

• ‘Lift and shift’ without a security assessment. Moving a workload as-is, without reviewing its configuration first, just relocates existing weaknesses into a new environment.
• Leaving default configurations unchanged. Not every Azure service is secure by default out of the box; each one needs reviewing against your own requirements.
• Treating security as a post-migration afterthought. Bolting on controls after go-live is more disruptive and more expensive than building them in from the start.
• Overlooking data residency and compliance requirements. UK-regulated data needs its residency and handling confirmed before migration, not discovered during an audit afterwards.
• No tested incident response or rollback plan. A plan that has never been rehearsed is a plan you can't rely on during an actual incident.

How OneAdvanced helps you migrate to Azure securely

OneAdvanced has worked with Microsoft for more than 30 years, and our Azure consultants support organisations through the full migration lifecycle: advise, assist, secure and operate. Our Managed Azure Services cover everything from initial assessment through to post-migration optimisation and ongoing compliance; see our guide to Azure managed services for the detail.

Security doesn't stop at go-live. Our 24/7 managed cybersecurity services, including a dedicated UK Security Operations Centre, continue monitoring your environment after migration, backed by identity security expertise across Microsoft Entra and managed infrastructure services spanning hybrid and cloud environments. For organisations that want their post-migration Azure environment connected into a single, secure work platform rather than managed in isolation, OneAdvanced IQ brings enterprise-grade security and compliance together with the data and workflows running on top of it. We work extensively with regulated sectors, including healthcare, legal, public sector and financial services, so we understand the compliance obligations layered on top of a standard migration in those industries.

Conclusion

A secure Azure migration isn't a checklist you run through once and forget. It's a plan that treats security as part of the migration itself, not a separate project that starts once the workloads have already moved. Understand the shared responsibility model, assess your posture honestly before you begin, and use Defender for Cloud to maintain visibility before, during and after the move.

If you're planning a migration and want a second opinion on your security plan, get in touch with OneAdvanced's Azure experts for a consultation.

Frequently Asked Questions

What is a secure Azure migration?

A secure Azure migration is one where security controls, such as identity management, data encryption and network protection, are planned and implemented as part of the migration itself, rather than added after workloads are already live.

What are the biggest security risks when migrating to Azure?

The most common risks are misconfigured identity and access controls, unencrypted or unclassified data, unchanged default settings, and a lack of tested incident response plans for the migration window itself.

What is the shared responsibility model in Azure?

It's the division of security duties between Microsoft and the customer. Microsoft secures the underlying infrastructure, while your organisation remains responsible for identities, data and access, with the exact split depending on whether you're using IaaS, PaaS or SaaS.

How does Microsoft Defender for Cloud improve migration security?

It assesses your security posture before migration, monitors workloads as they move, and provides continuous protection once live in Azure, combining posture management, workload protection and code-level security in one platform.

What is the difference between Defender for Cloud and Microsoft Sentinel?

Defender for Cloud protects cloud resources and workloads directly. Microsoft Sentinel is a security information and event management (SIEM) tool that aggregates and analyses security data across your wider environment, including but not limited to Azure.

How long does a secure Azure migration typically take?

It varies with the number and complexity of workloads, but a phased approach, assess, pilot, migrate in stages, monitor, is generally safer than a single large cutover, even where it takes longer overall.

Is Azure compliant with UK GDPR and data residency requirements?

Azure offers UK-based regions (UK South and UK West) and a range of compliance certifications, but compliance depends on how you configure and use the platform, not on the platform alone.

What is the NCSC Cloud Security Principles framework and how does it apply to Azure?

It's a set of 14 principles published by the UK's National Cyber Security Centre for evaluating cloud security, covering data protection, identity and access, and secure use of the service. It gives UK organisations a practical benchmark for their own Azure configuration.

How much does a secure Azure migration cost?

Cost depends on the size of the environment, the number of workloads, and how much remediation is needed before migration. A proper security assessment early on typically reduces overall cost by catching issues before they require rework.

Should I migrate to Azure myself or use a managed service provider?

This depends on your in-house Azure and security expertise. Organisations without dedicated cloud security skills often find a managed service provider reduces both risk and the time to a secure go-live.

How does OneAdvanced support businesses migrating to Azure securely?

OneAdvanced provides end-to-end Azure migration support, from initial assessment through migration to post-migration monitoring, backed by a 24/7 UK Security Operations Centre and more than 30 years of Microsoft partnership experience.