uPVC has to be fitted at the time of manufacture as it weakens the door if fitted after.
My door already had a catflap, I have the non magnetic Staywell, 4 way lock flap. When locked to in only, two of mine can still break out
![knackered :tired:](https://www.purrsinourhearts.co.uk/Smileys/purrs smilies/sleepy.gif)
When locked completely they do their damndest to get out and have succeeded once using brute force to prize the frame out of place a bit and pull the flap open. Problem with that is they couldn't get back in
![Evil Laugh :evillaugh:](https://www.purrsinourhearts.co.uk/Smileys/purrs smilies/evillaugh.gif)
So if I lock it I have to put a laundry basket in front of them so they know going out isn't an option but even then they'll sometimes shift it to have a pop, usually at 3am when it's guaranteed to annoy me most
![knackered :tired:](https://www.purrsinourhearts.co.uk/Smileys/purrs smilies/sleepy.gif)