HM Revenue & Customs publishes a deemed fuel only mileage rates in addition to the authorised mileage rates.
New fuel only rates ranging between 7p and 21p per mile were introduced on 1 July 2008 and are available on the www.hmrc.gov.uk website. These rates are dependant on the type of fuel (Petrol, Diesel, LPG) and size of engine (1400cc or less, 1401cc to 2000cc, Over 2000c).
If you are using the authorised mileage rates, you can only claim back the input VAT on the “deemed fuel element”. Also remember you must ensure, under rules introduced in Jan 2007, your employee submits a valid VAT receipt with their mileage expense claim for the amount of VAT reclaimed using this method.