I use three envelopes, It is the same address for codeword and the the others all go to 124, Royal Avenue, Belfast, BT1 1EB (offices of Belfast Telegraph) Sunday World office is round the corner in Library Street.
If you live in Belfast you can drop the crossword in, saves on postage
I messed up the codeword this week, I normallly photocopy and when completed copy to entry coupon.
I have not won since they moved from Commercial Court, used to drop the crossword (loved that other crossword very educational) in there and then pop
into the Duke of York for a pot of tea, just to relax after all that hard work. LOL
Good luck