'Late' potato problems...

You'll have seen the heading of 'Late potato problems', but that greatly underestimates the gravity of the situation because the taties are, quite literally, 'late' in every sense now because they're dead! Everything seemed to be going well, but then the leaves started to wither - just a couple at first - and then the whole lot died within the space of a couple of days, leaving eight bags of compost with what will presumably only be some fairly small potatoes amongst them.

I've got this afternoon (Monday) and tomorrow off work to spend some time on the garden, and I'll be seeing to them then, but I'm bracing myself for a fairly diminished crop. I won't be too devastated, because these very late 'lates' were pretty much an afterthought in an attempt to have a few nice, home grown potatoes to close the calendar year, but am just wondering whether anyone could advise me on what might have gone wrong. The varieties were Casablanca, Duke of a York, Charlottes and Carabinas.

One other query, too, in relation to this - and it's a general one about compost from various tubs and bags I've used this year - but, is it OK to dispose of the compost (bought in bags fron Homebase) by spreading it in the veg patch and letting it settling there over the winter? I was going to spread a layer of leaves under it and put the compost on top to weight them down figuring this might be a useful way of further aerating the soil. Would this be right?

As ever, any advice would be very gratefully received....