i have hard pruned ares over years and now a good time will probably re break with new shoots by end of october and will be strong enough to go through the winter but dont leave to late in the year as those cold frosts can damage and it can be good to use fleecing to cover during winter if young plant

Thanks, Scott - very reassuring!

Erm, I'm afraid I disagree with the previous answer - I wouldn't recommend it unless you're in a warm area of Devon, or near the sea. Cutting back hard now, in mid September means more growth will appear by mid to end of October, and won't have time to harden off before winter sets in, but if you live in a very mild region, you might get away with it. Personally, I wouldn't risk it, I'd simply remove minimal amounts where absolutely essential, and leave the major prune until late April or May next year.