[mdjlucan]

Can I trim the back

[mumofstig]

You can, but you'd lose the flowers, for a few weeks - at least, depending how hard you cut it back.
I'd leave it - it looks lovely

[Aunt Sally]

It is lovely.  I agree with Mum.  Leave it until the leaves start to fall before pruning.

[oldgrunge]

As MoS says, if you prune now, you'll lose most of the flowers for weeks. It's a lovely, healthy fuchsia. Leave it alone, and enjoy it.

[mrs bouquet]

Yes indeed it does look lovely, so I agree leave it unless there is a vital reason to have to gently cut the back out.   Could you pull the planter forward so that you can enjoy it more.   Mrs Bouquet