Begonias in Hanging Baskets

Depends what you call winter in the UK.. if the temperature doesn't drop below freezing then they'll be safe, otherwise I'd either supply heat or heel them in the ground.... dig a trench and cover your potted plants with soil and then plenty of mulch. If you have a greenhouse why not supply some heat and have your plants flower all year? If your greenhouse receives direct sun during most days you wont need much heat... I'd place stacks of large bricks in your greenhouse where they'd receive direct sun, they'd radiate heat all night.