Tree ferns come to mind. Can be expensive but will give you height and they allow light to filter unlike trees. They will like the shelter of a courtyard and normally evergreen depending on winter weather.

Other that will do well:

Box/Buxus
Winter Box/Sarcococa
Ferns
Eunonymous
Mahonia

I have just added a couple of photos of my daughters first home on my photos. It was a super place to relax. She inspired the neighbours too. Most were young and not wealthy but once they started making a feature of the back yard they found family, friends and colleagues chipped in with bits and pieces.

many thanks

I have a Styrax japonica in a tub . . . it has little white flowers in summer and the leaves are turning bronze-ish now; it is 6ft tall and quite slim!

There are three berberis that grow in an upright column, Berberis thunbergii Helmond Pillar, Helmond red, and a gold one whose name I forget. They aren't expected to get to much over five feet. The Pillar does tend to spread a bit as it matures but not too much. The smaller rhododendrons will grow in tubs in ericaceous compost but do be careful to get advice on small varieties. there are some attractive grasses for contrast and you can have large troughs for perennials and bulbs. You could also drill the walls and put troughs or hanging baskets on them. Don't forget that one of the smaller clematis could be trained on a wall. They like their roots in shade and their heads in sun. You can also grow gooseberries and redcurrants as cordons against a wall!

Many thanks for all your suggestions, I'm now looking them all up to decide what to get, definitely not getting clematis though! When I moved in that's all there was on one wall, it was out of control, I reckon it grew 6 inches each day, it had to go! And it attracted snails, hundreds, literally hundreds, of them!