have you watered it ?

I would give it a good soak for a hour and then let all the water drain away and see what happens in the next couple of weeks.

Some times tender plants that are small just dont stand up to the weather and it might of had protection of a greenhouse but unless heated doesn't keep out a hard frost

what part of the UK are you.

I'm wondering if it might be shock...is your greenhouse heated? also, I have had trouble with red spider mites in my greenhouse this winter and my Lemon Tree really has suffered and lost most of its leaves when I sprayed it with a bug gun. I have a small Olive Tree (In East Scotland) which has happily stayed outdoors on my patio right through the winter, so if it does survive, I would leave it outside next winter.

As it has new shoots it should be fine. Good soak as Gnarly says, and protect from extreme cold. Good luck and welcome to GoY!

Thank you. Yes I've watered it well. It's just lost nearly all its leaves so probably was really dry. I'm in South Yorkshire we've just had 2 really warm sunny days so hopefully that will have given it a boost. Than you for your advice.