Best time to cut back apple and damson trees?

[gibba8]

I have got 2 apple and 2 damson trees in my small garden. These trees have produced loads of fruit this year but need trimming/pruning/cut back (do not know correct term!) as they are getting too big for garden.
What is the best time of year to do this?

Some good info here
www.gardenaction.co.uk/fruit_veg_diary/fruit_veg_mini_project_september_2d_apple.asp, also check out the RHS site
www.rhs.org.uk/advice/profiles1205/applepruning.asp