Chris - Definition = OK mark; when the answer is "flanked" by RAF fleet, you get raffle ticket. I've taken a few liberties with the punctuation.
My take on mattrom's is that tick is half (demi) of ticklish (delicate), with sec as the definition.
Aristo -thanks for the welcome, but I'm going to have to withdraw. Rather stupidly, I realise that I'm not going to be around next week. I'm off for 2 weeks as of Thursday and I'm not sure about internet access. I don't imagine my withdrawal will have a huge impact but it's a bit embarrassing given that it's my first post for ages. I got over-excited by the prospect of your challenge!