I have been offered a position for a PhD with a well respected researcher in a good institution - but I got a really bad "gut reaction" from the interview, and the funding is not guaranteed (but he wants full committment from me before he applies for funding!) and do not want to accept the offer. He wants to know asap whether I want the position (he tells me he has hundreds of other potential students for the post). How do I politely turn the offer down?
thanks,
elm.

Just say no sorry and as quickly as possible to let others have a chance

this sounds a bit odd! tel him yu an oly take if if you have funding! and if he really wants u he will wait

if you really have decided to quit this opportunity, just tell him your situation. as he have mentioned he has other potential students, i think he has been used to this and can understand you. But did you applied to other institutions as well? if you only applied to this one, might this mean you will not study for a phd? consider it seriously if this is the case