In that subculture, of course, Ks and Big Ps could be all sorts of things...
Seriously, I think that they're actually getting frightened. No, not them. The Met (itself no stranger to the K or the Big P).
If anyone is ever charged, despite the incontrovertible fact of the sale of knighthoods and peerages over long years and including by both main parties at present, then, 18 months down the line, the Met would be looking, at best (yes at best!) at subjugation to the Mayor for London and to the Greater London Authority, and quite possibly at separate constabularies for each London Borough. And no more Ks or Big Ps.
They've been warned, and they've heeded the warning. Hence no caution when interviewing the man who must be guilty if anyone else is, as someone else clearly must be: they wouldn't dare charge him, so they can't and won't charge anyone.
Ks and Big Ps all round, then?