OK - my cats are clearly 'challenged'.

[Grumpyoldpersonwithcats]

Today we've had new French windows put in which open outwards (replacing a single door that opened inwards)
2 of the cats have now approached the doors (clearly thinking since the workmen have gone it is now safe to come back in) - only to leg it looking terrified when I opened the door for them.
Waiting to see the reaction of the other two and wondering how long it will take Lenny to pluck up courage to return.

My guess is that it will be a fortnight before they get the idea that the doors open the other way. And even then, they won't like it. You have messed with their territory

Ha ha. That is hilarious.

My parents had building work done and had a door blocked up. The car refused to acknowledge that it was no longer a door and would sit in front of it asking to be let out!

You have offended your cats, how VERY dare you. You now need to get the workman back in to rectify the door situation.

Lenny came back after about 20 minutes (left the door wide open for him so it wasn't too frightening). I have never seen a cat take so long to cross a threshold. Karl is now outside - miaowing to come in. Go to door - open door - Karl runs away. Repeat. 6 times in the last 10 minutes. Dear God what have we done?

I had a cat who would go out of the patio door but would never come back into the house through it. He would sit on the back door step to come in. Dullard cat slave would get up and go and let him in through the back door every time.