Some universities  or some departments in universities have very bad reputations so to  check a departments research quality look at their RAE scores 4,5 and 5* are the top three.

Find What are the  addition resources  that departments offer?

To check their teaching quality look for QAA scores which are generally out of 24.

Finding  a strong and experienced supervisor is essential for the quality of research programmes. The mentor should be a senior figure with subject-specific expertise that clearly overlaps with your own research, and you should also be able to tell a story about how (s)he will assist in your professional development (advice on publications, grant applications, etc).

Get the feedback about the  department from current research students or past students. You can easily find them on social sites like Linked In , Facebook , on university websites. Ask them relevant questions about department like  What input will other staff of the department have; will you present and receive feedback on your work in the department; does the department have a track record of successfully mentoring postdoc students  into permanent positions.