July-August is best. The risk is the weather, I would now wait.

August is the best time to prune it back into shape, it also helps the Beech to retain the browning leaves.

If very overgrown, then wait till around February as it will have been dormant for a few months and causes it less stress when pruning it back. Waiting will pay you back with a healthier hedge next year.

Yep, we do ours in August, this gives the hedge time to grow a few more leaves after its pruning before the cold weather sets in and this ensures good leaf coverage for Winter.

Thanks all, I have trimmed it and will give it a good prune in Februaryx

You're welcome Anita.