Think we have solved the problem. Cat comes to visit about the time I am cooking dinner, has a little sleep, NO FOOD FOR HIM, then OH comes home and it is off home (I hope). It is a very clever cat and watches me lock the cat flap and has stopped banging it as knows when it is not welcome. Only trouble is when I open it both ways about 11 pm it has had a sleep over but OH got up in the night and it was off like a rocket. If it stays too long the other twin comes and fetches it and I chase them both off home.