What is a 'Chair' in British academia? I understand that a 'Chair' is a traditional title of a professor in the UK.
Nowadays, what is the difference, if any, between a Chair and a Professor in the UK?
It is the difference between the role or job and the person who is doing that job.
The person has achieved the status and title of Professor. That person can take the position of the &quot;Chair of Computer Science at the University of Somewhere&quot;.
Sometimes a particular Chair will have been endowed or funded at a University and then a Professor is recruited to take that Chair. That  person could have  moved from another Chair at some other University.
Some of  the Chair endowments are quite old, like this example from 1702 in Cambridge: https://www.ch.cam.ac.uk/alumni/new-name-our-oldest-chair