If they're not hardy ones, you'll need to take them into a frost-free place for the winter. It's then that you can cut them back. So - watch the forecasts!

in this part of the country (north east essex) most people tend to leave the ones in the ground, where they are and trim them back every spring. i even leave my hardy fuchsias in pots outside, and have never lost one yet, even in the worst of weather last winter included. although. i am quite happy to admit i may be lucky.

sorry i should have said hardy ones. otherwise i put them in the g/house after the first really cold night, and then trim back

Yes, I have hardy ones that stay in the ground, and I cut them back when I see the new growth appearing. All my non-hardy ones go in the greenhouse.