As per the thread title really 
The previous owner of our house had cats, so there's a cat flap in the back door. This would be fine except that my one year old son has reduced the mechanism to a pile of broken plastic. It's more of a cat hole now which obviously isn't ideal!
Is there a way of blanking off a cat flap? The door is a plastic one. I'd very much like to not have to buy a new door!

The previous owner of our house had cats, so there's a cat flap in the back door. This would be fine except that my one year old son has reduced the mechanism to a pile of broken plastic. It's more of a cat hole now which obviously isn't ideal!
Is there a way of blanking off a cat flap? The door is a plastic one. I'd very much like to not have to buy a new door!