If you use “traditional accounting” methods (ie you record income and expenses by the date you invoiced or were invoiced), you claim capital allowances after buying equipment, machinery or a vehicle for your side-business. If you use “cash basis accounting” (ie you only record income and costs in your accounts when you are paid or pay money out) and buy a car, you can claim this as a capital allowance, but everything else must be claimed as an allowable expense.