I've had so many awful cat flaps that are very flimsy, broken by the cat and finally by ds2 climbing out of the stable door and standing on the sticky out bit. 
It might just be that we are a bit violent
including the cat - recently I came into the kitchen and found the cat flap had been shoved through the door and onto the floor leaving a gaping hole. I imagine she just sort of nutted it.
Anyway we finally have a new door, a really nice, heavy, antique door and I reluctantly have to fit a new flap in it - so I'm looking for a very strong and decent one. I don't mind paying a bit more for it, I just want it to last.
Any recommendations very gratefully received! 