I think they are hardy enough to be outside if planted in a sheltered spot, with good drainage, but pot-grown ones I think would be best brought under cover, in case the soil in the pot freezes. If it does, I think that would kill the Agapanthus.
What have you done with it in previous winters ?

Thank you very much I’ve left them out last year but lost 2 of them the soil had got wet and froze
Would they be ok in my garage do you think.and would I need to water them at all?

They will probably be all right in a garage, that's where I put mine.
I don't think you'll need to water them, they'll be dormant and you don't want them to become soggy.

As Meadowland has said, if you leave them outside you'll have to give them a good mulch.

some are not fully hardy so yes pop in the shed/garage and don't water until March/April

Thank you that’s great - and my job for tomorrow will be to put them in the garage - too dark tonight !