To some extent it depends on which direction the wall faces and what the soil is like - could you give some more details please? Also how long is the wall and what is it made of?

I would consider clematis, if you want a fast grower to cover the whole wall go for a montana clematis they grow pretty fast and cover large area's, you may be better off planting two either the same or another varaity of clematis... also honeysuckle is a great choice oh and you can't beat a Jasmine for the smell and they are evergreen. These would be my choices anyway, have all 3 growing in my garden. :)

If you are talking about doing it in a container, a vine big enough to cover 12 foot wide, 15 foot tall wall would need a container at least 3 feet wide and deep. A 15 foot wide, 6 foot tall wall would need a container 2 1/2 feet wide and deep.

Its direction is critical - if its, say, north facing and never gets direct sun, what you plant will be things like ivy, climbing hydrangea, i.e., far fewer options than a south facing with full sun. Knowing where you are in the UK is important too - a north facing wall in London is a vastly different proposition from the same thing in Yorkshire in terms of cold.