If your package is unopened and arrived via Royal Mail in the UK, you can write "Refused" across the shipping label and bring the box to your local post office to have them scan the tracking barcode as "Refused/Returned to Sender." It may take a little longer to arrive and doesn’t provide you with tracking, but it should get the job done.
If your package is opened or used, contact the Support Team for a Return Merchandise Authorization (RMA) number, which should be referenced on the exterior and interior of the return package. It’s recommended to use a shipping method with tracking on your return package. The return address is:
RMA #____________
Unit 20 Radar Way
Christchurch
DORSET
BH23 4FL