Hello JS, I put my acers in the polytunnel for the winter. Although they are hardy I cant trust the freezing Fen blasts that we get, I reckon they are just this side of delicate to cope with that. Check out my acer photo's & Zen blog, the colours are incredible at the moment. Keep well.

I think it probably depends on where you are in the UK and what your winter temps might be, as well as the 'chilly wind' factor as Bizzyb says.

If your area isn't too cold, then you could just insulate the pot with bubblewrap, and place it in a sheltered corner for the winter. In many areas, Acers survive outside perfectly safely if you just take a few measures.

I don't do anything to protect my Acers in pots, and they seem ok after the winters. That's not to say It wouldn't be beneficial to do so though.

back home in Devon I would be happy to leave acers out all year round. Here in the open flatlands the Fen blasts have an altogether different chill factor to deal with. Dorset is superb Bluespruce, I have family in & around Christchurch, had many happy holidays there. I miss the Jurassic coast but the Fens hold a fascination by it's very contrast & quite a different approach to gardening requirements. Friends lost established acers last winter round here due to leaving them out.
It would be useful to know what county you grow in JS & if your garden is sheltered etc.

I think as Spritz says-- and it goes for any plants in pots-- its stopping the roots from freezing & dying that is really important even if the plant is dormant.
one pot inside another and insulation between can help as can clustering plant pots together, especially if one is too large to move, wind can damage them physically too if the blow over

They're 'ardy. Leave 'em out. Never lost one yet to winter cold. Phil J

I was amazed, after the harshness. length and depth of snow here last winter, to find both my 10-year-old Acer and 4-year-old Olive survived in the ground outside.

I still think that in pots, they're more vulnerable - as rootballs can freeze. In the ground, yes, I agree - I wouldn't give them any protection....anyway, it makes sense to 'be prepared' rather than lose a plant in a pot.

Certainly doesn't do any harm to give them extra protection. The real problem with roots that freeze, is the likely process in the UK of freezing one minute then thawing the next. It's that process that can do the real damage as apposed to being frozen continuously for longer periods.

I live in east anglia near the fens and mine survived outside with no care last year. They have only been in three years and do really well. It's not the cold as such that bothers mine, it's the ferocious freezing fen winds that blast across this part of the country.