My mate uses his own car for business - he claims his mileage back at a fixed rate per mile which he puts on an expense claim at the end of the month.
He has now been told that he has to include "a receipt" for his petrol with each claim otherwise the company cannot claim the VAT back - apparently some European Court ruling.
The company are happy with the current arrangement, it is apparently bureaucracy for the sake of bureaucracy and helps to keep the bean counters in post.