Mid to late autumn or early spring.

Pot grown plants can however be planted at any time when there's no frost in the ground.

To some extent, it depends on what you're planting - some shrubs (Ceanothus for instance) are best planted in Spring, though the vast majority can be planted now.

Point taken Bamboo. I agree there are a few shrubs that don't seem to settle in well in autumn. Ceanothus being one of them

I'd add Garrya to that list, along with Yucca and Nandina domestica Firepower, Anchorman - like Ceanothus, they seem cold vulnerable when they're small and newly planted, so okay in a mild winter, but we never know what its going to be like, do we... wouldn't it be just great if we knew!

Oh it would Bamboo, after the last few years long range forecasts I,ve given up believing them......

I've long ago stopped believing forecasts for 6 hours in the future! ( or 3 for that matter!)

thank you everyone for your comments I do have another question when is it best to prune my plants they are garden plants... many thanks

Various plants need pruning at different times. If you tell us what your plants are I'm sure we can help.

I have just planted one I bought from B&Q can't rmember the name but I have buddleja silver anniversary

The Buddleia should be pruned hard in March.

thank you for that :-)