It's the first time I've grown tomatoes and started them off in the conservatory where they've grown healthily for just over a month With a good amount of sunlight and I water them every day. I recently bought a mini greenhouse for them as they've grown to about 2ft tall. Since they've been in the greenhouse (positioned The same angle as they were in the conservatory) they have lost their healthy green colour. The leaves have become weak and some of them are folding/curling in on themselves. Need some help to revive them, could it be because they are too close together in the small greenhouse?

Tomatoes needs a lot of sun and fresh air, Where do you live? Is it cold? Is this why you have them in a green House? If so... open a side of your green house and let them breeze some fresh air they must be suffocating. And yes you need some space between each plants. They like to spread their arms and they need a stilt or wire cage and of course vitamins.