My opponent must have been appalled at the course of the game since this is not the sort of position you want when desperately needing a draw. 18 Bf1 consolidating and bashed out my move. White is already quite enough material up without grabbing apparently irrelevant pawns. Now Black's bishop is coming to h3. I wasn't going to tell my opponent in the post-mortem, but I completely missed this move.
Retreats really are much, much harder to see than blatantly aggressive moves.
Fortunately I'm still on the board but in a state of shock. I was very keen to live up to my newly acquired status. The only sensible way to defend against mate. At least the onus is on Black to find a way through now. Seductive but inaccurate.