'But why did they hijack Labour instead of, say, kinda king the Libs, which was a party on the rise at the time?;
No. The Establishment is terrified of real Labour because Labour is the people. Therefore the Establishment puts its own people into Labour in order to control what Labour does and it helps them rise to the top. Labour has now changed beyond all recognition and is no longer a people's party that can represent any threat to the metropolitan elite. It is now full of millionaire barristers from Oxbridge who are are the metropolitan elite and who are miles away from ordinary people.
Also, the Establishment knows that the people are much more likely to vote Labour than LibDem and therefore Labour is much more important to be part of, if control and power is the objective.
Now there is a new peope's party - UKIP, and the establishment doesn't control it, although it will do its best to try. This new party challenges the metropolitan elite over every one of its sacred cows - the EU, global warming, immigration, political correctness etc. That is why there is panic in elite circles. All they can do is shout that UKIP are not politically correct, that they are racist etc and let their media try to trip up UKIP. But UKIP aren't politically correct, so the Establishment's best tactic can't work, and UKIP aren't racist so that doesn't work either because the public know the game and they are ignoring the metropolitan elite's desperate attempts to fool the people.