How do I know if a lab is good in its field? So far I've checked RAEs and if they've published a lot of articles (though I'm not sure how good these articles are). Are there any other good indicators?

The number of students and postdoctoral researchers in a lab is a good indicator, although there are many good young scientists at the start of their career who will be very good supervisors (they have more time to dedicate to students and research). We put a lot of emphasis in this forum on finding 'good labs', to encourage people to look further that the reputation of the university as a whole. A decent RAE and a bunch of papers is about as good an indicator as you're going to get without advice of others in the field.

You should now concentrate on the research projects that most interest you. When you go for interview you should be given the opportunity to speak to people already working in your potential supervisors lab, they'll be able to tell you more about what the labs like to work in.

Ask your tutors/lecturers for advice. see who they have heard of. They dont have to be famous but future employers must know who they are or they will be less likely to consider employing you. Your supervisors name is the most important thing on the cv at the end. sad but true.

A word of caution... RAEs are for deparments, not individual labs. Some advice... visit the lab(s) you might be working in. Is it BUSY? Is it CLEAN and ORGANISED? And, more importantly, does it have the EQUIPMENT required for your research?