When to crop the tops of blighted potatoes?

We have taken ours off as soon as it became more than a few leaves, they were sprayed but obviously too late. Although the spuds have been on the small to medium side they were perfect in all other ways.

A few other beds on our plot are holding on so we are watching daily.

I have 2nd and maincrop, Estima and Valor, both have been affected. I take it that the tops have to be cut back to rescue any tubers, however if the tops are cut back and the resultant cleared area sprayed would the top growth return, and therefore the tubers carry on growing?

The question is - can I hold out to maximise growth until my tops are completely blighted or am I best to stop the tops now?

I planted late

I would say you have no choice but to wait. It's either that or hundreds of marbles.
I've known folk to wait until the crop is well blighted and then chop and get a half decent crop, the odd week or two at this end can help immensely. The important thing is to then wait for a week or two, and then lift.

I'm a bit of a soap box person on this matter, but for anyone in the mild South West, the best blight protection is to sow early, no later than the middle of March. Make the most of what the local climate offers. Covering the potato bed to warm it at the end of February is far less heartache than dealing with a lost crop. That only works for short seaon 1st and 2nd earlies of course. I have no answers for maincrops where proper organic practice is preferred.

I no longer grow maincrops as a serious attempt, Engineer, I guess that's my organic, or more accurately,  sustainable answer. I pick what potatoes I want from the 1st and 2nd early varieties.

It was time to move on. If a crop isn't sustainable on a semi regular chemical-free basis in my climate, I don't see the point in growing it. I have just 12 King Edwards in the ground, but they're more a side bet than a proper attempt, a decision made in the light of last year's wonderful blight free season. If they fail, it's only a small part of the potato crop.
I'm sure someone will correct me if I'm wrong, but the Soil Association allow regular chemical spraying of potato crops and yet still certify the crop as organic. I'm more interested in the most sustainable growing I can manage. Spraying spuds doesn't fit that bill, so the delicious maincrops are out

Good against blight, but not so tasty on the plate in my experience. I ended up taking a load of last year's crop to a local barbecue as jackets to clear them from my store.