If you do a PCH deal you won't have to worry about BIK rates as it's personal not business. You could still claim the 45p per mile (up to 10000) then 25p after that (might not be 25p, can't remember exactly but definitely lower).Sorry Qazser, didn’t see your response but thanks for the confirmation. Company has traded for over 2 years so ok there, it needs to go through the co to take advantage of the 0% bik rates - although I’m not sure if you could still do that with a pch deal - never had a company car, always done it through pch in the past and claimed mileage.
To work out what is better you just need the total cost per year and compare that to the total mileage allowance you will claim. If the total cost per year is more than your annual mileage expense claim then would be better doing it through the company. If not then better to do it personally and claim the mileage expense.