My statement was in response to the OP being surprised that the vast majority of the people on a VS were white. If the criteria for representation is 'wider society', in this case I assume that to be the general UK population. If over 80% of the UK population is White, it is likely the case that there will be a significant proportion of White applicants in comparison to BME applicants for vacation schemes. It also follows that, if the criteria by which we measure representation is indeed 'wider society', then I see no issue with White students making up 50-80% of a VS demographic. This would be perfectly representative of a 'wider society' where the White demographic is significantly larger than that of the BME demographic. But often times there seem to be people unhappy with this - but why? If one is aiming for representation, and that representation is, almost self-evidently as you feel, measured by wider society, and wider society is predominantly White, then what's the issue? It would somewhat be the equivalent of going to Washington University of Barbados and being shocked that the vast majority of students are Black.
Where it concerns the criminal justice system, I think there is a strong case for having a representative legal profession, but insofar as white-collar corporate law, I am not convinced that this is a necessity.