That's not really what I was saying Steve. The actual costs claimable are listed at the link, as well as the private miles you can't claim for. If you use traditional accounting rather than fixed mileage rates, you can buy the car as a capital allowance item, so I guess that would be where you might need to justify your Ferrari? Hard to simplify without getting deeper into it all, but keeping all the receipts for 6 years might be worth it for you, but fixed rates are an awful lot easier.
https://www.gov.uk/expenses-if-youre-self-employed/travel
I think that we are talking about 2 different things. One is the costs to a business of running a particular car as a company car, and the other is the rate of acceptable reimbursement if I as an employee choose to use my personal car for business miles.
Here's a real-world example from a former colleague. He's a director of a food company, very much a high-up. The company bought him a Merc S500e with all the toys, reckoned to be list £100k or so. He will spend a lot of time in it, they can afford it, he can afford the BIK tax, happy days. So this car is likely to be worth half list in 3 years time, by which time it's worth £50k. So the fag packet says that it costs £17k a year depreciation, plus whatever in fuel and insurance for his (say) 20k miles. Let's say that it's £25k a year, all up, cost to the company. Can the company claim back the full amount of all this against profit? Of course. It's an essential part of running their business, same as paying him his salary. He gets the car to take home, pays the BIK on his tax bill, uses it in his own life, where he covers (say) 5k miles a year. Great. So in this instance as you say the car costs WAY more than 45p a mile, it's a pound a mile (fag packet).
Our man tires of his tax bill so he decides to buy the same car and bill mileage. He shells out the £100k, owns the car, takes on all the fuel, insurance, servicing costs, and bills his employer £1 a mile. That's what it costs him after all, £25k, 25k miles, of which 5k personal, he picks up £5k of that, his employer £20k. He now has a £100k car on his drive for £5k a year, fully fuelled, all up. This is a LOT less than the BIK bill would be for such a car at 40% tax (maybe 45%!). Are you really suggesting that HMRC will tolerate this? I don't think so. If they did then I for one would have a 911 in the garage and the business would be heavily subsidising it, out of my untaxed company income. This is not the case because my accountany and HMRC would roll their eyes and say "You're havin' a giraffe! Now stop taking the mick, 45p a mile, if you choose to drive a Porsche then that's good for you but you'll pay for it!"
