You are growing typical NE varieties, Fraser, that are flowery and therefore, break down easily when cooked. Try some waxy varieties, such as Desiree or Nadine. This year we bought some seed from Lidl, of all places, 'Nicola' and it is a super firm potato with good flavour. Your sand soil has nothing to do with the problem.

i had the same problem recently, i spiked them and cooked them in the microwave on 2/3rds heat . no problem all held together and tasted great

thanks everyone some good advice will give it a go and will report next season cheers

When you buy your seed potatoes read the label fully - it usually says if the potatoes are waxy or creamy - this kind don't go floury. Casablanca are nice waxy earlies.