im just about to complete my undergrad degree and have been offered a fully funded masters+PhD place at my current university. research is an area that id never ever considered, but this is such a fantastic, once-in-a-lifetime opportunity and worry that i would always regret it if i didnt give it a shot.

my plan has always been to try and get onto a postgraduate course in Speech & Language Therapy, however competition for places is fierce. this masters+PhD offer is guaranteed (as long as my application is accepted, which my tutors seemed fairly confident about), but i worry my heart wouldnt be in it and i would drop out after id done the masters.

im not sure what advice im looking for really... im so utterly confused, this has all happened so fast and ive got to make a life-changing decision after only one week of contemplation :-(

It certainly is a tough decision to make when you only have week to make your decision. I'm really going to oversimplify things now and maybe sound a tad patronising (which I apologise for). Your heart has to be in doing a PhD because they really drag and it's about doggedness more than anything. However, and I'm not sure how the masters and PhD programme works, but if you do the masters and then get to design the research proposal for the PhD in something you're really interested in (such as speech and language therapy research) then it's quite a good decision. However if the PhD has to be in researching something that you're really not interested in, then I wouldn't go for it. Your heart has to be in it.
It's a shame that you have such a short time frame, because you could have tried to get on a postgraduate course for speech and language therapy and have had the masters and PhD programme to fall back on. As it stands (I know I'm stating the obvious), it's a decision only you can make. I suppose it also depends on your long term career goal, because if doing a PhD doesn't fit in with your overall plan, then there might not be much point, since you're essentially training to be an academic and researcher. However, you could do it and then try and do the postgraduate speech and language therapy course afterwards.
I'm sure someone else will be along tomorrow to give you some better advice. Good luck in whatever you decide to do :-)

I can only advise that if you are going for a Masters then a Research Masters like an Mphil (compared to an MSC) could a better option if someone wants to pursue an academic/research career. If I am not mistaken, you can extend your Mphil to PhD within 1.5 years....