doing a masters at bristol with a undergrad from uwe

Your friend is wrong.

Provided the course provided an appropriate background for the masters, it's fine.

obviously it depends on what your undergrad was in and what your postgrad will be in, but if you are looking to do a masters in the same subject with a first then you should get in. things like work experience and internship will play a large role perhaps

Thank you! What sort of amount of work experince should I aim for?

Work experience isn't necessary or even probably relevant for an academic subject such as maths.