Motor Vehicles - Capital Allowances and Expenses

Does anyone know where I can get a good summary of the various rules and practice applying to self employed re capital allowances and expense (including finance cost) treatment of buying a car with your own money, using a car loan, hire purchase, or car lease.

Also, what are the rules when you have owned a car for a number of years and you then use it for self employed business purposes ?

Thanks

Any suggestions ?

Thanks