Blight? Dickeya? Blackleg? which is it?

Last week I spotted a very poorly potato on a friends allotment where I have a pumpkin patch. It was pulledup, bagged and quarantined. Initially I thought it might be blight but now not so sure as I've watched several other plants following on, so I've seen  the sequence of events. We are just outside York. IT is very hot. We only had blighty days on July 3 and June 21. I could see that some of the plants were labelled as Desiree but am not sure about the whole crop.
Anyway
1. Foliage looks pale
2. Foliage turns yellow or has brown patches
3. Leaves curl up
4. Plant wilts
5. Tubers are still at small stage but I think I found a couple starting to rot.
Stages 2-4 only take about 48hrs. Havent seen any stem rot .... yet!
So is it blight? dickeya?   blackleg? something else?

Agreed!

 Thanks, all! I will pass on the info to the allotment holder. Would you suggest she pulls up the lot or wait till each plant succumbs?

I've got some dodgy spuds. The ones in the containers.  I took the foliage off and hope for the best. Whether I will get a crop off them remains to be seen. They'd not flowered though