Try a tropaelum speieosum (Flame Flower) from thompson and morgan for about a tenner. Lovely climber with loads of red flowers. Put the container, (about 15" should be big enough) in the shade and let it grow through the pergola. Cut it down every autumn A lovely plant

You could choose climbing roses, clematis or both for your pergola. If you do decide on clematis, make sure it's group 1 or 2 for pruning purposes, or else you have to cut them right down in early spring, which would be difficult if they're scrambling among the roses. You'd need large containers - I'd say half-barrels would be good.

Welcome to GOY, by the way - I live in Somerset, too!

If you look on Goypeadia under Climbing plants. Clematis, Wisteria even Arches lots of pics to give you an idea of what you would like.

Thank you all for your suggestions. Someone has given me a packet of Morning Glory Seeds. Would they be happy in a pot?

Yes, certainly - but they're annuals, so it might be good to plant something permanent as well, for them to clamber up. :-))

Passion Flower is a good creeping plant, my brother has one on his fence, it blooms very well , if not there are planty of climbing Roses out there nice scented ones would be brilliant.
If you are going for climbing roses try Cants of Colchester who deal with Roses of all variety's

Thank you for your suggestions Hijuju. They are now on my list for consideration:)