Hello Standen1, hedge laying is cutting most of the way through the trunk of the "tree" low down and lay it down forming a thick stock proof hedge - probably not one of your requirements but can be done on an ornamental level so you get a stylish thick "solid" hedge. Its not that difficult, especially on a short distance and a new hedge. You could also espalier a hedge which would look quite smart. http://www.hedgelaying.org.uk/styles.htm
Beech would look good - green most of the year but retains its leaves through autumn and winter which turn bronze or copper coloured which retains the screen. https://www.flickr.com/photos/bushmonkey10443/6507694201
Saw the troughs (£70 each?) - expensive when you could get 80cm - 100cm whips for about £1 a plant - http://www.hedgenursery.co.uk/all-hedging-a-z/i-fagus-i-beech/i-fagus-sylvatica-i-common-beech.html
These are the people I used (1500+ plants) excellent quality lost about 4 plants and my 3 year old hedge is16ft in places! My beech/hornbeam hedge is about 8ft although I need to prune it into shape.
Thinking about it - what about fruit trees - trained along wire? depends how much work you want to do, whether you want something a little different or purely practical. If you want a year round screen and something you don't have to do much with - Beech or yew.