[belto]

I erected my polytunnel early this year, January, planted my tomatoes amongst other things.
As they developed the leaves curled and went brown, I thought this was due to the excessive heat in the Tunnel but the tomatoes started to go brown and then the main stem went brown.
I am confused, is this tomato blight or excessive heat or both.
I have since read on here that one should not water in the evening.
Should I just water the roots and not the leaves and when?
Has my tunnel enough ventilation? There is just one door & 6 X  18" windows , should I create another large window and the end.
If is is blight will the spores carry over into next year, or should I fumigate the Tunnel with a suitable method

[Pescador]

That looks like blight to me. You should water at the roots and not wet the leaves.

regarding carry-over, as long as you remove all remnants of tomato plant material and any dropped fruit you'll be OK. There is no evidence of soil-borne resting bodies or spores.

[sunshineband]

Yes, as Pescador says, this is Late Blight and removing all the infected material is the way to go now, I am sorry to say. I also have this issue right now in  my tunnel and "One is not amused" The spores are able to get through mesh windows or be blown in when the door is open. No getting away from them.

Do collect up all the fallen fruit, as well as every scrap of leaf, and with nothing to live on, any spores around will die. Mostly advice is to burn infected material, and this does at least stop spores from spreading, but sometimes it is not practical to do this. Mine goes in the local green waste, which is sterilised during the composting process

Advice about keeping foliage dry is definitely worth following,although I did this and still have blighted plants and if next year you see curled leve sof brown patches, cut the leaves off to restrict the spread through the plant. This might mean you can get some ripened fruit. Outside I always now only grow blight resistant varieties, which is worth considering nder cover too of course

Sad though, when you see all your plants go like this after tending them so carefully