I was chatting with another practicing accountant, who told me in discussion that they work out a clients (self employed) mileage allowance using HMRC advisory fuel rates.
This is how he explained it to me.
They add all his fuel costs incured during the year; disallow private use %; divide the result by the advisory fuel rate to get the "business mileage".
Then, multiply the mileage by the the HMRC mileage rate of 45p / 25p to arrive at an amount, that they claim is legitemate business milege claim.
Is this correct? Or even legal?