My situation: I applied to 5 DTPs and was called for an interview for the project that I liked the least (lol and screaming internally).
If successful at the interview, I imagine I won't have a lot of time to decide, and I am probably keen on accepting as I wouldn't have any other offer.
The PhD is funded by one of the UKRI councils and it should start in October 2021 - my question is: if I were to reject it at a later stage (if I find something I like more) would that be allowed without any consequences? And would the position be given to the next candidate in line?
I obviously don't want the supervisor to lose the funding because of my decision.
Meanwhile I have been in contact with a postdoc who's work matches all my interests, but she will know if she receives funding only in June so I would only be able to apply in the summer - if things go well would it be too late to reject the other offer? Also, she is applying for funds from the same council as the other project, but in her case the university would cash-in the fundings and do the selection process itself, not the council, so I don't think they would know if a candidate has already won one of their studentships - right?

I know it sounds silly to overthink everything so much in advance but I would really love any suggestions from people who were/are in similar situations, particularly with UKRI councils. Thank you so much !

For my experince- the supervisor gets the funding and then run their own call to hire someone- ITs done none by the research council. They inform the research council of who they hired at there reporting periods.
If you get offered it you can then reject it- it doesn't look great but can be done. I would advise that if you're going to reject it make sure you're given a lot of notice and not saying it two weeks before you begin.
From my own experience- after offering someone work a few months ago I stating planning for their start that, the week before I got an email saying they were going else were- after 3 months I now have to re-interview.
Equally there nothing to say that that post-doc will even call you for an interview if they get funding- people pick the best person for the role.

Personally, I would focus on doing a good interview for the one you have- Project can always change to suit the candidate's interest.

It's been my experience managing UKRI studentships that UKRI are very open to the student changing direction in discussion with the supervisor, unless it's really radical (like changing field). It's eminently possible - in fact quite normal - to end with a thesis title that's a long way from the project proposal.

It's a bit of a half-truth that leaving after you start will have a negative impact on your prospects. A bad Uni/prof may even suggest this because it's certainly bad for them - as they're potentially left with PhD funding for 2.5 years, which they won't be able to spend without internal funding to top it back up to 3 years. It may well harm your chances of success at the same institution with the same prof, but won't generally be problematic. Word does not travel as far in academia as most believe.

Rejecting an offer (before you've taken any salary), by comparison, carries no stigma I've ever seen. It's the Uni's fault if they don't insist on a decision by a date.

Irrespective it's essential you go into the interview mentioning none of this and being enthusiastic. This isn't dishonest, it's being professional and making the most of every opportunity. Just getting an interview is by no means a guarantee of an offer (I average about 20 per studentship); if you say you're not actually that keen you'll likely be immediately written off and the decision won't be one you'll need to worry about..! :)

I'd just end by noting, it is always risky in academia to rely on a future promise or opportunity of a post. Naive, well-meaning academics often slip into giving vague promises of future opportunities to students, when anything not signed is extremely open to the whims of HR, senior management, funding councils, etc., - an academic that's not a VC is seldom in a position to 'guarantee' a future opportunity to anyone.

Hey, thank you all for the replies! From what I gather, it can happen that a prospective student first accepts and then rejects an offer.