As you may be aware rates for using your own car for business purposes are 45p a mile for up to 10,000 miles & 25p thereafter.
With fuel pricing going up daily the 25p rate is even unlikely to cover the fuel let alone the other running cost of the car.
One way around this is to by splitting some of the work you do by creating a self-employment and then assigning a proportion of the mileage to that.
For example, if you do 20000 miles a year, as a company director you would only be able to charge back £7000 to the company.
If this was split between the company and the self-employment, then your are entitled to 10000 miles @45p for each role. This means the allowance would increase to £9000.
I hope this was helpful, for lots more tax tips and strategies get a copy of our 71 ways to save tax checklist https://bit.ly/2YQbhvr