topping the affected parts of the earlies for about 10 days seems to have done the job. I've harvested about a pound from 2 plants and all were fine, (lovely potato salad,lol). My friend in the next village has lost about a third of hers to blight, she said.
The maincrop don't seem to be affected here either, but most of mine are in containers, the earlies I had planted in clay rich soil to break it up and as it is quite far from the house may forgot to water them most times, don't know if that makes a difference.