It really needs a much larger pot - it gets 2.5metres in the ground, so would be much better off in a pot that's around 18 inches to 2feet deep and a minimum of 12 inches wide. Were it in such a pot, you could leave it outdoors all winter without any worry, especially where you are. As it is, you can still leave it outdoors, but place it in a sunny sheltered spot, up against a wall - its only vulnerable to freezing through the roots in a terracotta pot, so if its really, really cold (below zero night AND day for a week) you'd need to insulate the pot to protect the roots. Otherwise, in the sort of mostly mild winters we get these days, should be fine.

Thanks Bamboo, a bigger pot needed straightaway OR would it be better off in the ground?
Clematis seem to come and go in our garden and I am afraid of losing this one.
Many thanks for two lots of help so close together.

I have it in the ground and I think if you have a spot for it, it would do better in the ground.

They all do better in the ground, like most plants, then they can achieve their full growth potential - it can be planted during September. It's a rather good red, this one, I must say...

Thanks to you both. We shall choose a spot carefully and put it in the ground.