Have just started a phd. I turned down another phd (one I was really keen on) in favour of this one, as I thought this one would be great. I get here and find there's a complete absence of what I was promised, am very unhappy (esp. as I turned down the other one).I want to quit this one and reapply for the other one: am worried that I've already turned it down once so would it affect my chances of being offered it again? What will my referees think/write about me quitting this one?

You can always try to reapply to the phd position you turned down. But it is possible that they found another PhD student. Call and ask whether the position is still free. Go to your referees and discuss your problems with them. May be they also have good advice. When they know your reasons they will most likely support you! Good luck!

Thanks, Britta! The phd I turned down was actually a programme (a bit like a Wellcome trust one) which accepts a fixed number of students a year. Hope your Phd is going quite a bit better than mine!

Went through something similar myself a few years ago.. if they don't find another student quick, they'll lose the grant/funding. I'm afraid the chances are quite slim as you will need to reapply (equal ops) and so on. Let that one go (it's out of your hands now anyway) and concentrate on making the most out of the one you have.

Get in touch with the people you turned down and see how the land lies. As far as your referees go as long as you have good reason to quit, and they are aware of that they should be favourable to you. However it is only human nature for any future supervisor/employer to look on your leaving your PhD with some suspiscion. The earlier you leave, the less effect it will have on both your current supervisor and your prospects of starting again somewhere else.