Returning goods to the UK

Anyone have any experience of what you put on the customs form for this?

I bought a camera in the UK just on 2 years ago, with a 2 year warranty. It has broken… Firm are happy to replace it and send a new one (probably to my sister in UK) but need the old one back to check it.

What can I put on the customs form to avoid paying VAT and customs duty?

For a start put the value as zero - it’s broken after all, and put “returned goods for repair” in the description.