Do it now. I cut one back nearly to ground level about 3 weeks ago. It's growing back very strongly now.

Thanks, I thought I read here somewhere to do it now, but then when I googled I could only find 'Autumn" answers...

I think if you did it in the autumn it would not have much time to re-grow before the winter, and maybe what's left would suffer in a cold spell like last year. But the experts know better than me.
Good luck anyway :o)

I think I'll try to do it now, it makes sense and it looks wild! I

I'm sure you'll be doing the right thing.