A level subject requirements for medicine

Is Sociology an acceptable third subject for Medicine in the UK
(Along with Chemistry and Biology)? Is Maths compulsory or preferable for any particular universities?

It's fine for all universities except Cambridge, where you would need a third science. Have a look in the Medicine forum for further information about medical schools.

As above, if the 3rd subject isnt specified, it can literally be anything - all the Uni is interested in is the grade. So, don't worry about what you think 'looks good' or is 'relevant', pick the A level subject you will enjoy studying as that is where you are most likely to get a good grade.