Frost proof pots/planter

[john9159]

I am looking for plant pots which will withstand frost for dwarf fruit trees.
I have several trees which are to be planted in pots but need advice on frost proof/resistant types to choose, and a supplier.
I also need guidance on the minimum size of pot to choose.
My location is Manchester where we may get temperatures as low as -10C.

[burnie]

It's not just the pots that need to survive, the root ball can be frozen and the plant could die, I put my containers inside over winter, the smaller ones are plunged in the border soil in my greenhouse.