45p per mile here but they don't pay my entire year's insurance like yours seem to be doing.
Sounds like you're going to end up in some sort of halfway house between a company car where all expenses are paid for and you claim back business fuel used vs a private car where you are responsible for expenses but claim back a 45p per mile rate to cover it all (supposedly).
Personally, i'd much rather be wholly one or the other or the tax implications will be more messy than I could be bothered with.
FWIW, my car averages about 35mpg and this gives me a fuel cost of roughly 20p per mile at the moment, so the proposed rate would likely cover fuel but you're still left to pick up the tab on stuff like your servicing, new tyres etc.