@CautiousLurker01
My DC went through Physics admissions this year. They did both PAT and ESAT.
Your son will NOT need to do TMUA for Warwick. Maybe they needed it in the past, but not now.
Here is what my DC said about these tests.
ESAT - was generally not too difficult as to the level of questions, that are A-level based. BUT it was difficult because it was really time pressured - with a large number of hard A-level questions. So - what is key in prepping for this test is a lot of practice, and TIMED practice.
BTW Cambridge NatSci also uses ESAT - so if he is prepping for Imperial, there is no reason not to apply to NatSci....
PAT - had longer and more complicated questions. Less of them than on ESAT. Pressured, but in a different way.
As to applying / not applying to Oxbridge, but applying to Imperial.... Imperial is as hard, or harder to get into than Oxbridge. All of these receive a huge number of international applicants (it is very popular with Chinese students) - who spend years prepping for entrance tests in weekend schools. As a result - they score really high --- in PAT, for eg. majority of top 100 scorers are international.
Oxbridge has an extra benefit of interviews - where a local child who is passionate about physics can demonstrate their problem solving abilities - and thus compete with the foreign students that are great in acing tests.
Imperial does NOT have interviews, so just go with the test scores....
As to whether you need to help you DS prepare for the tests with a tutor or not - it sort of depends on his level of motivation - and ability to self-study. Does HE want to have a tutor to help him focus?
Also - he should try one practice test and see how he does now - to see his baseline. Then you can see if he needs to practice more the "exam technique" - or still need to solidify actual A-levels content.
Finally - Warwick has a strong physics program. Birmingham does as well - in addition to Manchester. At the BA level - he will not be specialising in Particle Physics anywhere really - he will be getting the basics of all areas of physics, that is required for future specialisation. Specialisation happens in Masters, or PHD - and many people move for Masters from the Unis where they did their BAs.