Blight in my Greenhouse East Sussex

That is not blight, it is grey mould (botrytis). It is a problem I'm suffering with too, caused by the wet weather and colder conditions. You can try and reduce humidity in your greenhouse by keeping vents open as much as possible, even overnight if it's not too cold (mine are open tonight). Also it's a sign that your plants could be too crowded, so you can remove some of the lower leaves or any that are touching.

Try and water only in the mornings and don't splash it around, just water the roots gently.

You need to cut out the diseased parts as soon as possible. Spraying with Bordeaux mixture (usually used against blight) will help.

 

I agree with John . If it was blight you are likely to see the main stem starting to go black.

Get more ventilation to the plants. It is better to have a lower temperature than to have it warmer with a high humidity. As long as they get enough sunlight/daylight they aren't too bothered about high temperatures at this stage of the growing cycle.

If you have cucumbers in there as well then it becomes a bit awkward as they prefer higher temperatures and humidity. So, if growing both, you should have tomaotoes near the door (keep it open) and cues near the far end.

 

At this time of the year we keep our greenhouse door and vent permanently, fully, open.