I have to say that I'm not a great fan of trying to grow potatoes in bags for Christmas. I would say that the foliage is likely to get diseased and finish growing early. They will be cold and suffer from poor light. Before the supermarkets sold 'new potatoes' at around Christmas time they used to get a large tin in the autumn and fill it with the small, freshly dug potatoes with a little dry compost and bury it in the garden and unearth for the Christmas season.

What I would use also is 25 litre buckets instead of bags you could then wrap bubble wrap around them to help keep them warmer and maybe some sort of heat mat but still it will be a struggle unless we have a warm Autumn early winter.Light will be a problem and the only way around that maybe artificial light and the only thing that springs to mind would be 12v waterproof LEDS these are dirt cheap but you would have to know how to set up and wire up.I would imagine that first earlies would give you the best chance

Thanks both of you! It is always good to hear about the negative side of things before going ahead. I was wondering about the light and heat though have loads of bubble wrap to put round the containers if I did decide to go ahead. I would definitely only plant a few just in case of a disaster!