These trees needs a tree surgeon in to cut back to 5ft .

Or take out completly and its hard to get anything to grow for the many roots.

But I have a corner where a neighbour has a manageable hedge.

I am growing clematis and rhodendrums and have got it planted out nice and colourful.

Good luck .

Do you get on well enough with them to have a word about chopping to a more acceptable height?

I know it can be a bit of a minefield when approaching these issues.

Otherwise, think of the usual woodland shade varieties for options.

I believe there is now a new law regarding hedges, particularly with reference to the dreaded Leylandii, which now gave the local planning authority to require them to be cut down to a reasonable height.
See article: http://news.bbc.co.uk/2/hi/uk_news/politics/4596685.stm

My neighbour 's leylandii grew about 15 ft tall and eventually blocked the sun from my patio. I asked him if I could cut it to 7ft, promising to take the offcuts away etc.
He agreed and after 3 years or so it's a really nice shaped hedge.
At first it was a sight, but now i wouldn't be without it.
Put it to him. Good luck.

Many thanks for your help, we dont really know the people as they back onto us and there is a line of 15-20ft trees in the way ! We will try asking nicely and if not then have to look at alternatives.
I dont know why people do this as it just looks a straggly sight. They bought the house with an 8-10ft hedge two years ago and have left it to go wild.

Maybe they don't know it's bothering you. Maybe they're nice people and would be delighted if you'd volunteer to attend to them ?
Best thing is to ask and if it's not on you'll need a plan B, which no doubt a fellow GOYer will come up with.
Check Bertie's suggestion(above) if necessary