I think it has to be IP lawyers and investment bankers. IP law partners can earn in the millions, and most senior investment bankers earn a couple hundred thousand a year. I think accountants (or management consultants like you say) still earn a high salary that is in the 50-100k range, but I think the highest earners will be concentrated in the big 4 since they literally dominate like all of the market share for accounting. I'm not well versed with the other two professions, but I imagine that a big position in a pharmaceutical company would be over a 100k, still not as good as investment banking I wouldn't think. International organisation I have no idea, but I don't think organisations like those running on the principles of international welfare will be paying out extortionate salaries to its members - even the UK prime minster only gets 100k.
When people say the highest earners in the UK, everyone's immediately thinking of lawyers and bankers so that's a good indication of who's earning the big money. I'm still in A-level though so this is just my speculation, though I do hold offers for degree apprenticeships at an accounting firm that is just below the big 4 (Grant Thornton), commercial bank (HSBC), and investment bank (UBS) so I have done a bit of research into career progression and whatnot. I might end up just going to university for law, since law is interesting and I have an offer from LSE, but that's my opinion on top earners.