Tomatoes don't need insects to polinate
If night time temps are consistently below 10c a lot won't set fruit. There are some varieties thst have been bred that will set fruit down to 4c. Also if daytime temperatures are above 32c for a while that can also cause problems, that could be an issue in a greenhouse
I have read they don't need insects to polinate. So how do they pollinate?
Also does that apply to sweet peppers?
Due to the way their flowers are constructed, neither need insects for pollination, although both can benefit from the occasional tap of the stems to shake the flowers around a bit to make sure.
Somewhere around midday is the best time as the pollen will be drier and looser (I just do it whenever I happen to think of it, which could be at any time! 
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So the equivalent of wind born pollination?
When you say both, you mean sweet peppers as well?
I am thinking if both, I may attempt to block access to the greenhouse with insect netting, where possible. Windows mainly. At least should reduce green fly etc.
Thank you cc
My understanding is that when insects help tomatoes pollinate, it is the vibration from the insect that does it. Bumble bees are reported to be helpful tomato pollinators ('buzz pollination"). I imitate this by going around to each tomato flower and gently flick it a few times with a finger. It seems to work.
If you look at a tomato flower up close, it is mostly a closed structure, stamens are close around the pistil. Pepper flowers IMO are more open (aubergines are sort of in between). I think peppers would be more effectively pollinated by insects, but probably it could happen without insects.
Could tomatoes be wind-pollinated? Maybe!
