The english taxation system allows a proportion of car expenses, tax free (tax -deductible, if you prefer) that proportion has to be exclusively the proportion used for business....so Mr. self-employed is supposed to take start and stop odometer-readings every time he jumps in the vehicle (note I didn't say "car"
) and annotate the purpose of the journey.
Overall, the taxman is reasonable....I had a bit of a row on one occasion when he disallowed tea, sugar and milk costs (very modest!)
I suggested that the Ford Motor Co's Chairman's office cocktail cabinet full of Whiskey, Brandy and the like, would not be disallowed.
I also asked if toilet rolls were going to be disallowed, and could I claim a portion of my haircut costs as my working-week was 50% of the total "growing time"
Didn't get the brew allowance , but the bogrolls were allowed