@Jessica Booker @Ram Sabaratnam I got a call last Wednesday for a vacation scheme offer which I was unable to accept because my dates for another offer clash (spring) and the other scheme (summer) dates are during term time (I'm international). I still managed to express my enthusiasm for the firm and ask if I could be swapped on to the DTC AC to which the grad rec said that would be absolutely fine but I haven't received any email confirmation since, should I email them? also for future reference am I better off not telling them over the call that I'm no longer available? (sorry just feeling a bit paranoid they're going to rescind the offer)
From what you have said, I sense they are probably waiting for you to confirm in writing you are declining the vacation scheme offer. Unfortunately saying this over the phone isn't sufficient - they will need something in writing from you first and I suspect then they will reference the direct TC process from there.
I would email them confirming you are declining the vacation scheme offer and that as per your phone conversation you look forward to hearing more about the direct TC recruitment process instead.
You would have needed to tell the firm one way or another you were not accepting the offer - I think it is better to do this over the phone so you can show your enthusiasm for the firm (positive tone is much easier to pick up in a call than in an email) and also discuss what the alternatives are. So it is not an issue that you called them. Whatever way you told them, the process from there on for the direct TC process would have been the same.
I doubt they will rescind any offer to convert to a direct TC process, but this is likely to include further assessments - firms rarely will just offer TCs off the back of VS assessments.