When should my tomatoes go outside?

Hi, i was wondering when my tomato plants should/could go outside? i think i started some off a bit early and they have got to a good foot, foot and a half tall, will they be ok? what should i do with them

If you mean into their final positions (growbag or ground) then not until after the last frost in wherever you put them. I.E now in a well heated greenhouse, mid May in a cold greenhouse and start of June outside.

My (6 inch high) tomatoes are currently in a greenhouse in the greenhouse where the temperature goes below 10C for about 2 hours each day. Some people say that this is too early but it seems to work for me. They will go into the borders of the polytunnel in mid May.