When you move from a company car (esp. if fuelled) to a private car (abet with allowance and business mileage) you need to rethink your transport choice.
For example; with a company car I use to drive to the airport and park up – when I took the allowance, I used a taxi. You only get 10k miles pa at 40ppm, and then its 25ppm – no point doing more than 10k pa business miles in your own car.
And whereas previously I’d happily drive abroad and then fly back for the weekend, in my own car – taxi to airport, fly and then hire car at destination.
Money can be made with an allowance and business miles, but you need to be smart with what you buy and how you use it.