You should keep a record of any mileage you do on company business and include this in your Expense Claims (see also How do I claim Expenses?) as an agreed rate per mile; HM Revenue and Customs have a threshold rate per mile up to which no tax is due so if you claim in excess of these rates then a P11d will need to be completed for the excess and you will need to pay extra tax.

You should not simply claim the cost of filling your vehicle with fuel as part of your Expenses Claim.

Please note that travel to and from work is not normally considered mileage on company business.