Thanks for this Doug. As tumbleweed suggested - it is possible that my trees are some strange type which might not be amenable to pruning in the way you've suggested. Just for my piece of mind would you have a look at these pictures of the trees (not brilliant quality I'm afraid) and let me know if your advice still stands.

http://uk.f2.pg.photos.yahoo.com/ph/...=/1ea7&.src=ph

Cheers
Jon