It looks fine at the moment so I would leave it alone. I had one on a wall in my last home and it took some years before it flowered. If it got too large then you should prune after flowering I think. The RHS website should give you more info.
Hi spottysocks! It really depends on which variety it is, mophead or paniculata? If it's a mophead,which blooms on last year's growth, remove last years blooms in spring and gently prune to next pair of good buds down the stem. If it's a paniculata,which blooms on this year's growth, these can be pruned to 2 or 3 good pairs of buds from the bottom of the stem. Hope this helps, good luck x
Thanks for the advice, much appreciated I have the mophead variety, but after looking for the next pair of good buds further down the stem it's quite a way. I just seem to have a couple of buds on the top, the rest of the stem is just woody. I'm going to wait a few more weeks to see if any more buds appear and if not, I might give it a trim.
That looks to me like the variety that flowers on last years growth. If you cut it back now you won’t have any flowers ? You should only need to prune it if it starts to outgrow its space and be prepared to loose flowers for a year.
Thank you all for your good advice. I think I'd better leave well alone this year, I don't want to lose any flowers, as they're a lovely deep pink colour.