Jayne wrote:

I often see it recommended that plants are brought indoors before the first
frosts - could somebody tell me approx. when that would be?

Jayne (who hasn't been a UK gardener for long!)

Technically anytime in the UK;-)

But generally, Oct - Dec..

Best suggestion is to ask other gardeners local to your
area/microclimate. Where abouts are you?
//
J