Who does my son go to as regards retaking a year of his academic tutor isn’t that great?

[Duckbi11]

He’s contacting student support but who else should he talk to?

One of his module leads will be able to help. Has he tried speaking to his supervisor? Even if they aren't great they'll have dealt with this before so will know the process to advise on etc.

The Student Union will also be able to advocate for him

Department Academic lead or Student support

You mean, he failed and needs to retake, or he’s switching programme or something?

The senior tutor in his academic department.

Within his department:
Module convenor
Director of Studies or Director of Education
Senior Tutor or Welfare lead

In the University
Faculty Welfare lead
Student Counselling/Wellbeing
Student Union/Guild advisor/ welfare lead

All of the above is good advice, OP. Only if your DS’ personal tutor knows your DS well is the tutor even likely to have input on this.

Best wishes to DS.

In this situation, a personal tutor would mostly be signposting where a student would get advice and help to negotiate what they want. To permit a student to intercalate or repeat a year is way beyond a personal tutor's role or indeed, power to effect.