If you cannot afford to pay your hire purchase payments, you can terminate the agreement yourself at any time – but only if the creditor has not issued a default notice.
If you want to go down this route, you simply need to make your request for termination in writing (sent by recorded delivery). The creditor will then reply by letter too, detailing how to return the goods or how they will collect them.
If there is any outstanding debt or shortfall after this, you can offer to pay it back in affordable instalments.
It’s better to approach your creditor before you default on payments to them, that way you will end up owing less money due to the way in which shortfalls are calculated.