Towards the end of the 2015 general election campaign, when the consensus was that the Conservatives would not win an overall majority, David Cameron went to Twickenham for an early morning rally of local Tories. That he was spending valuable campaigning hours in what was then Vince Cable’s seat should have made those of us in the media realise what was afoot. A Tory majority was coming, even if most of us were too focussed on the TV leaders debates and fripperies such as Ed Miliband wasting his time wooing the “comedian” Russell Brand.

Another sign that the Conservative high command had access to research which confirmed the Liberal Democrats were even weaker than they looked, and that a slew of seats were about to fall to the Tories, was the extent of Cameron’s deployment in the South West of England where the Lib Dems then held many seats.

The Tory anti-Lib Dem operation at the election was completely ruthless, a thing of wonder, which Lib Dem leader and Deputy Prime Minister Nick Clegg and his friends did not quite see coming. Clegg was a decent man (I was far too hard on him throughout the coalition) but his naivety is apparent in his new book. The Tories eat the Liberals every once in a while. And Nick Clegg was on the menu from the moment he agreed to stand in the Downing Street Rose Garden and marry Cameron in the heady days of May 2010. At the nuptials the Lib Dem leader might as well have worn a t-shirt emblazoned with the word “yet another sucker.”

Indeed, the most convincing Tory defence of the coalition deal from more cynical Tories was that it lent the Conservatives cover, deflected some of the blame for austerity and would result in inevitable disaster for the tainted Liberals.

That is what happened, of course. But there is an irony. Doing in the Lib Dems – as Cameron was more than justified in doing, that’s politics – ended up being the undoing of David Cameron and his premiership. Taking the decision to take out the Lib Dems earned the Tories their majority.

It meant that Cameron had no excuse on an EU referendum. He had no escape, because his manifesto committed him to hold a renegotiation of Britain’s terms of membership and a vote by the end of 2017. If he had fallen just short of a majority or had to enter a coalition with a diminished but not obliterated Lib Dem grouping he would have been able to say: “I’d love to be able to hold a referendum, but the Tories didn’t win so my hands are tied. Drat, what a shame.”

He might then have faced a leadership challenge, from a minority of furious hardline Eurosceptic Tory MPs angry that he had fallen short again at a general election. But the contest would have been a messy affair, with no obvious replacement, and Boris probably being taken down by Gove and Osborne albeit in different circumstances from those which pertained this summer. At the head of a minority government, or a confidence and supply administration in league with the Lib Dems, Cameron may well have survived in office for another two or three years.

Instead, he won the 2015 general election outright, because the Tory campaign was too good, too efficient. Cameron dished the Liberals and rushed off down the road that led him in little more than a year to the exit. It’s a funny old world.