Any time at all. I pruned several very large 15 foot buddleias before xmas down to about 3 feet high and they're starting to bud up again already. To be honest, there's very little you can do to hurt them so go for it.

I agree..I took the top branches off mine in Autumn,and anytime now,I will cut it well back,as lots of new growth is appearing..Tough as old boots,so it will be fine..If you don't cut it back hard,,you may only get flowers at the top this summer..

Thanks folks I'll wait for it to stop raining,long wait I think.

You haven't said which variety of Buddleia - B. alternifolia and B. globosa are pruned immediately after flowering. The more common Buddleia davidii is hard pruned in spring, with long growths shortened in autumn if necessary before winter winds arrive - where you are, I'd certainly wait till mid March before doing it, Kent can get pretty cold, unless you're near the coast, in which case, any time from now on.

Well, with respect Bamboo, i'd have to totally disagree with the pruning of any buddleia but especially davidii. We've grown these thugs (beautiful thugs though) for decades in parks, housing estates, car parks and any old scrub land. I wouldn't have any problems cutting them hard back at any time of the year if needed.

I do ours in March. I think it's erasier before all the leaves grow.

"Cut back last year's buddleia stems" one of this week's jobs from Gardeners' World

I cut mine down to between 3ft and 4ft in the autumn to stop wind rock. They get a second prune in Spring to remove any weather damaged stems. My globosa and alternifolia get cut back after flowering.

I looked this up last year, and my book said end Of Feb. I was surprised that it also said this is the time to root cuttings, so I pruned it and stuck the cuttings in some compost in a plant pot and nearly every one of them took! Good luck...mine was Bud. davidii by the way.

This is Buddleia we're talking about here. Just hack it back whenever you need to

so long as its not B. alternifolia or B. globosa...