Colmm, to blow means to bloom, according to Chambers, so a bloomer is blowing, and 'the gaff, say' is a sounds like, it sounds like gaffe, a mistake, bloomer.
ChrisE, I think it was the other thread which Norah was going to delete?
Indent = (to) order, Chambers and EC is city, though I can't remember why! It's been a crosswords stalwart for as long as I've been doing them (and Bradfords Crossword Dictionary lists EC under 'city').
Curiosity got the better of me, so I investigated. EC is the postcode prefix for the East Central area of London, which is commonly referrred to as 'the City'.