What to do next

if you definately have blight, you need to cut all of the foliage off and burn it, your potato's should stay perfectly fine in the ground for a couple of weeks, providing the soil is kept dry!

If you plan to store them, remove the blighted foliage and leave for a couple of weeks for the sun to kill off the blight spores before digging up.  If you plan to eat straight away, you don't have to worry and can dig them up immediately.

Either way, check for tiny tubers left as these may carry the blight spores and reinfect next year.  

Mine got hit last week - looked ok two days before.

The potato council's own blight website still says

If you grow potatoes, bag, bin, and, where possible, burn any affected plants.

http://www.potato.org.uk/publications/gardeners-advice-potato-blight

so that's what I will carry on doing 

Thanks for all the replies 
I have checked and it is blight will return tomorrow and cut off all the leaf growth above ground .
I harvested enough yesterday To last for a week or so .
I have a single row planted lates nothing showing on them yet but they are at the other side of the garden so will have to watch them carefully .
John