Brycey, I live in County Durham and only grow tomato's outside in a very sheltered south facing spot, normally cherry types and not always successful, last year was a wash out even the greenhouse tomato's gave a very poor showing with tough skins and a bit watery.
Saying that we gardeners never give up, I sow seed in one third compost one third washed sand and one third fine grit then pot on to half compost half grit and sand.
My main pots twelve inch plastic with large holes in the base and no crocking will be set on the gravel bed in the greenhouse ready and the small pots then potted into the large pots and watered in. My out door pots will be lined up along the walking area (don't ask, they do get the odd knock as I scramble about) and when or if we get sunshine they go out into my sheltered area. Cool nights a fleece over them works, a snap frost it is back into the greenhouse.
You could cover them on cold days with fleece even newspaper but the main thing is to keep them out of the cold winds, that will turn the leaves blue as well as your fingers.