Got my BSc and MSc at the same university as that's where I live - it is ok to do a PhD at the same uni again (can't move) or will that count against when it comes to applying for jobs later?

My supervisor to be told me that sometimes you are best staying where you are - you know the staff, how the department runs etc. If your interests lie in an area that fits in with the interests of the dept you are in then why go somewhere else that might not suit your research? Hopefully it shouldn't affect job prospects as long as the uni you are at has a good reputation.
Good luck! xx

I will be staying on at the same Uni as my BSc for my PhD. Although it's a different department, I know I'm very happy with the Uni and city and don't believe it will adversely affect my prospects in any way.

The prevailing wisdom is that students should move institution in order to expose themselves to different academic influences. However if you have family commitments where you live nobody is likely to complain that you stayed in the same place.

It's certainly true that you need to change institutions after your PhD. But if you're already at a well-regarded department as an undergrad there is no necessity to change and it won't affect your job prospects.