Someone told me that if you quit a PhD. half way through, you could never do another one. Is this true???

No - you may find it difficult to get a place (particularly with the same funding body), but it is not a rule. For most UK research councils if you give up before the end of your first year, the supervisor is allowed to re-advertise the studentship. If you give up after this your supervisor will be unable to get a new student to complete the work, without applying for new funding.

If you are half way through an unsatisfactory PhD (and most students will find their PhD unsatisfactory at some point) it may be worth sticking with it. Another 12 months work could see you with a completed thesis and then you can move into whatever new field of research you are currently being tempted by.

I have recently decided to give up on my PhD and start from the beginning at a new uni, new project. I am almost 2yrs into this one but after certain health problems and difficulties with my experimental work, have decided to start fresh. I have thought about giving it another try (after all it's only another year!) but I do not think it will get me there after all. I believe that I can manage to start over, and just want to hear some comments what other students would of done in my shoes?!

I am settled into my PhD now but I hate the city I moved too. Have dabbled with the idea of going elsewhere and taking an MPhil from here. But then I probably wouldn't get another post.