i,m sure i read some years ago the cause is a limy soil. maybe some other member,s may be able confirm if this is true.

When we grew potatoes on alkaline soil, we lined the trenches with fresh grass cuttings to make the soil acid. But I would also select the potato varieties which have some resistance to scab. Growing potatoes in bags is an option but very time consuming as regular watering and feeding is required and I have found it only worthwhile to grow early varieties as by the time you harvest maincrop, they will be dirt-cheap in the shops.

Thanks for the answers. I'm defiantly going to try growing in buckets next year, although it seems like shame when I have so much open land on my plot.
We'll see.