(Aagh! I'm not hitting 'Submit' but AB keeps thinking that I am!!!)
Number all of the receipts and keep them in a ring binder in numerical order. (Small paper receipts can be attached to a sheet of A4). Ensure that the 'Expenditure' cash book records the number of each receipt, so that anyone auditing the accounts can quickly tie the two together.
Also keep a record of all business mileage and, at the end of the year, include that as an expense at the current permissible rate.
https://www.gov.uk/expenses-and-benefits-business-travel-mileage/rules-for-tax
(Note that, if those rates are used, no additional claims relating to vehicle usage can be included).
That's all there is to it!