We need a bit more info. Annie, where are you in the UK, which way does the spot you are wanting to put this screening plant face. We could give you lots of advice only to discover you are 300 metres up a hillside with a northerly aspect.

How tall and wide do you want this plant to get as well as the info Moon Grower has requested above. If you don't know which way the area faces, sun or shade and what part of the country you're in are critical.

Remember that containers should also be about 1/4 the ultimate total height of the plant, or they cannot hold them erect, or provide enough water or nutrients to keep it healthy--and therefor, thick enough to screen!