I would personally just claim the AMAP rates no to overcomplicate things (45p per mile up to 10k, then 25p thereafter). These cover all car expenses, including the purchase and running costs
Whats is AMAP rate ? and how capital allowance on car (use in business) is calculated per mile ? From what I am aware, car expenses are separated from car allowance ?
Whilst you can claim capital allowances, it seems a bit overkill for just one property.
Expenses and allowances are not tighten to minimum, e;g 3+ properties. It might go 3+ months you don't need to visit property but if thinks goes wrong with house (which usually happens at all the times), you may need to visit for 10 days or so regularly to get it repair, so all that is expenses.
I imagine HMRC would contest the 20% business use also. That's one in every five days that you visit the property, which seems over the top? If my landlord turned up once a week I would move!
This calculation is based on miles used for business vs private, and all is recorded in books. Landlord will not turn up unless you need them but once Landlord inspected property and finds out there is work to be done, e;g roof leak or other problems, he will need few visits until it get fixed.
Side note and I hope you don't mind me asking but how are you declaring the income on the tax return? I am concerned that you refer to yourself as a 'self-employed landlord'.
It's all recorded and declare through property pages. Self employed term is used just referring you work for your self.