My recent experience of claiming compensation may be of use to some here. I was booked NCE-LCY last October, and the flight was cancelled around 24 hours before I was due to fly. I was offered a flight leaving an hour and a half later to LHR which would have meant arriving home around two and a half hours later than planned. On that basis I believed I was due compensation, but it took some time. I set out in the first mail why the regulation should apply, but the answer I got back said that as I hadn't been delayed by more than four hours compensation didn't apply. The answer was wrong given the late notice of the cancellation. I replied on two further occasions, each time receiving in reply a fairly garbled version of what the regulation actually says. Finally I sent a polite mail saying that as we didn't seem to be in agreement I would just pass the matter onto CAA and fill in their form. Within days I had a mail saying compensation was payable, and soon after it was in my bank.
I think the key lesson is get to know the regulation, and be persistent if you're sure it should apply. The escalation paths also seem to work well.