In case anyone reading this is concerned about unequal supervision provision, I can give more information on the safeguards that are now in place. I supervised extensively in Cambridge during my PhD, for ten different colleges, more recently than the Varsity investigation.
For each module there would be a recommended number of supervision hours. For those I covered, it was usually 8-10 per term (I think with fewer for Easter term as there's less content). Colleges were not allowed to give fewer than the minimum, and shouldn't generally exceed the maximum either. In the supervision training session I attended (organised centrally, and mandatory before you can be signed off to supervise at any college) this was strongly reiterated. I then had to write reports on a centralised university system in the final week of term for each student, which would contain a summary of the progress of each student, my estimate of the degree classification at which they were working, and the number of supervision hours they'd received (including how many if any they had missed). The main purpose of this was so that the student and their DoS could review and discuss their progress (you would normally have a termly meeting with your DoS for this purpose), but I suspect a side benefit is that the data on supervision hours was then collected centrally and colleges could be regulated.
As an aside, colleges could authorise more supervisions in certain, special circumstances, either if a particular student was struggling with a module/part of a module or if there was a more general problem such as illness. For example, one of my students had a chronic illness/disability which had had a detrimental effect on their performance in the previous year, and I gave them one-to-one double-length supervisions the following year, which was one of a number of measures the college put in place to help support them academically.
My approach was to give nearly the maximum recommended number as standard (to include, in addition to the weekly supervisions, generally a revision supervision in Michaelmas, a mock and mock exam debrief in Lent and two revision supervisions in Easter). All ten of the colleges I supervised at paid for this ungrudgingly (and whilst I never supervised at Emma or Murray Edwards, one of the ten was Queens').