Hmm, difficult. First the restriction of a pot, and then lack of light, so there aren't many choices, particularly for things which flower, unless you simply use tall, flowering perennial type plants such as Phygelius rectus varieties.

You haven't said where you are in the UK, but if in warmer regions, a large pot with Fatsia japonica, which isn't a climber; Fatshedera lizei is another evergreen with attractive leaves, and there's a variegated variety of it too, but it will need some support to remain upright in the form of canes or similar. Garrya eliptica can be trained to grow against the wall, but again would need a very large pot eventually, and I wouldn't recommend it if you live in a cold part of the country because of being in a pot. Otherwise, Hydrangea petiolaris, which is actually a climber.

I'm with Bamboo, Fatshedra (Fatsia crossed with Ivy, but only 4 to 5 feet high), would be the only plant which would fit the bill. Several varieties of Ivy but nothing which would be colourful.

Thanks for your responses - Im oop north so colder climate. But thanks for the ideas!