@Walrus

If you send it back to their freepost address it will cost them £2:50, So please don't do that.
And make sure you don't write what you think of them on it in permanent marker first.

Reform UK
FREEPOST RTLT-ZXHY-KSDC
83 Victoria Stree
Lordon SW1H OHW

Mine arrived today, already in the post!