I'm afraid you should leave it alone - listed as prune group 9 by the RHS, which means pruning should be carried out in April-May, or after flowering.

Thank you Bamboo. I'll wait then, tho' it has only just finished flowering & the berries are not yet formed.

Hmm, well here's the link to the advice - but the other reason not to prune now is its too late in the season - pruning now might induce new growth which won't have time to harden off before the weather gets cold, though a light trim should be fine

https://www.rhs.org.uk/plants/details?plantid=1305