Join the club, Robert. I don't know anyone who has claimed 'success' with Christmas potatoes. We tried, just the once, this year and have the same result as you describe. Maybe further south in, say, the Channel Islands or even the Canary Islands?????
I prefer growing potatoes in the ground rather than in bags but, if I were to try with bags again in spring, I would use either a good peat-free multipurpose compost or a 50/50 mix of garden compost and garden soil.

Thanks for your comments bulbaholic its good to know its not just me I will try your suggestions next time round

Never had any success either, but it seems to be lack of water which is the problem. Never had any luck getting water into them without them rotting though.

Same here. Tasteless marbles. Waste of money.

Thanks for your comments Haha and merry christmas when it comes

I have grown early potatoes in bags for the last few years and have found that feed and watering has been critical rather than type of compost. I have grown Foremost and they have been good. I would still say that for the best results you cannot beat earlies which are grown in the ground. As far as growing earlies which have been conditioned to be grown later in the season for Christmas, I have found to be a waste of time. Not only does the cold and rain give them a hammering but they are more susceptable to potato blight and slug damage. Best to visit the supemarket or use the old fashioned method of storing freshly-dug potatoes in a large tin and burrying them in the ground.