Mid March at the earliest

Usually April is optimum....but make sure that if they start coming up, protect any top growth from frost.

You can also try a couple of spuds you've dug up in July in a tub....for a bit of fun.

Chuck em in then give them some protection when frosty and you'll have King Edwards for Christmas dinner

If you haven't already bought you seed potatoes, I would suggest that if you intend growing in a tub then you buy early potatoes. They will produce tubers nice and early and at a time when they are at their most expensive in the shops. You will enjoy new potatoes, freshly harvested to your table. You will have to wait a lot longer for the King Edwards and they will be dirt cheap in the shops by the time you harvest them.

Thanks for all your advice :)
I have already bought a few King Edward seed potatoes, but I may plant them in July and try to get a crop for Christmas ...
What varieties are early potatoes ... ?

King Edwards are more expensive than most other spuds even in winter. I only know because my partner refuses to eat any other type. Our Tesco Metro and Sainsbury's town store only sell them at festive times like Easter and Christmas, and I think it's because they are dearer than the others and so sell less of them.
Yes, the big supermarkets have them but no way will I venture into one of those. Greengrocers here in Exeter don't have them very often because of the price.
It's worth planting them for winter crops in my opinion, they are never cheap to buy.
Great versatile spuds; the very best roasties, chips and mash.

Thank you both.

Snoopdog, Steragram is about 60 miles away from me.
I know a garden centre just down the road where they sell loose seed potatoes. I usually buy them there :)
I've tried Rocket in the past so maybe I'll give Homeguard a go this year :)

Well Hywel two nice earlies I've had are Lady Crystl and Casablanca, if you like the creamy waxy sort rather than the floury kind.
Snoop I no longer have a bike and the main A40 doesn't have cycle paths anyway. And if I did and it did the answer would be much as I'd like to visit Hywel I will save up for the petrol or bamboozle OH into driving me!

Sue,
I have a couple of bikes you could try but find neither of them will go up hills any more. I bought a new one quite recently but it has the same problem.

Thank you Hank. Sounds as if you and I have the same problem, I wonder what it can be???

Thank you Sue. I'll see if I can find those varieties.