2 down duty
21 down might be tacks - sounds like tax - as in duty
I'm not sure, but then again, I never am. I have put site for 27 down. Again it is just a guess. Means place and S1 is part of London. I also have knot, but I have no idea why, lol.
I think the Big Ben one is TACKS and maybe to do with Ben Ainslie the sailor and tack is movement in sailing! Just my way of thinking anyway and sticking with it lol