Thanks for advice.

Update is that flap is down now and both are using it. Our semi feral isn't though which surprises me somewhat - think she may get the idea soon.

The nervous male was the first to get the hang of the flap which flabbergasted me as I would have bet good money on him taking ages - but treats did the trick!

The female is still a little suspicious. We have it locked during night hours and I saw her giving it a paw bashing around 6 am in the hope it would open.