According to some unofficial sources..... Englands first head of Intelligence, Head of MI6, was one Mycroft Holmes.
Not really, the guy was basically the conduit of ideas through which all of the nomenclatura's chatter flowed, but he was basically just an advisor, an interdepartmental one.
That is both more and less than what you describe.He was basically a form of broad-knowledge analyst, but Holmes said he didn't have much in the way of ambition or the desire to put overly-hard work.
And from what little I recall, he was not much of a shmoozer.
Maybe and advisor to M or even Q, but not M himself.Especially not in those years when patronage and proper connections were even more powerful.