If you are registered for VAT, you must charge VAT on all VAT taxable supplies of goods and services that you make. 'Supplies' include day-to-day sales as well as anything else that you sell or invoice for, such as assets and commission, and anything else you supply or take out of the business even if you don't charge for it, such as loans, gifts and anything used privately. There are some exceptions.
VAT is payable on the full value of any supplies made, even if no VAT was charged to the person or business who received the goods or services.
If you receive goods or services as full or part payment, you must account for VAT on the full value of the item sold, rather than the amount that you charged the buyer.