Bring both in before the first frost. Banana needs repotting too.

Thanks but in doors or greenhouse and when do I repot them?

Anywhere frost free - preferably not indoors, you just want to stop exposure to very low temperatures. So long as your greenhouse doesn't get below 5 degrees C. that should be fine.

the other option with the Canna is to decant from the pot in September, cut down the topgrowth to about an inch, separate and store, buried up to the necks, in dry compost in a box or container. Pot up around March, water and move them somewhere warm to start them into growth ready to go outdoors when risk of frost is past. Otherwise, leave them in their pot until March, and then decant. split and pot up separately, again moving them somewhere warm to start them into growth.

You can just leave the banana in its pot till March, then pot into something larger, unless its making a bid for freedom already with lots of roots hanging out of the pot, in which case, you'll have to do it now.

Thankyou that is really helpful and I shall probably go with splitting them in September. Thanks again.

I forgot to say, if you're going to do this at the end of September with the Canna and store them in dry compost, its a bit like storing dahlias - cut the foliage off and leave the bulbs on their sides to dry out a bit for a week, then put them in a container. If you're going to repot, just plant them straight away.