Tim Ross and Tom McTague’s Betting the House, a new account of the 2017 general election, develops a Conservative blame game.  Who was responsible for the failure of Theresa May to increase the Tory majority – indeed, to return to government without a Commons majority at all?  More light will be cast on what happened when Lord Ashcroft’s The Lost Majority , his study of the election, is published shortly.

In the meantime, one might start by challenging the conventional wisdom, and ask whether a boost was ever likely.  This site argued during the Tory leadership contest that the new Prime Minister should seek a fresh mandate and call a general election.  Once May made it clear that she would not do so, we were much more chary of the prospect, since she had committed herself, and were not among the enthusiasts pushing for one.  We were worried that “voters hate unnecessary polls” and that “elections are not always as straightforward as they seem beforehand”.

That said, the Prime Minister had the polls in her favour when she called the election – and, crucially, the English and Welsh local government results, which came between the election being called and polling day itself, were very good ones for her. The Conservatives gained over 500 councillors, won eight councils and took the West Midlands and Teeside mayoralties.  John Curtice wrote that it was the best Tory election night since 2008.

“I have now been involved in elections for 20 years,” Gary Porter, the Chairman of the Local Government Association, wrote on this site, “the first being the 1997 General Election, where, if I am being honest, I have encountered a range of reactions from open hostility, to being neither loved nor hated, to these elections where the overwhelming response was generally an outpouring of genuine joy to see us on the doorstep.”

It follows that something went wrong for the Party between those contests on May 4 and the general election that took place little more than a month later on June 8.  What was it?  You might expect ConservativeHome to say, in the wake of Mark Wallace’s formidable accounts of the rusting of Tory machine, that CCHQ’s campaign department and Patrick McLoughlin and Stephen Gilbert and Lynton Crosby were responsible.  Certainly, that the Party won 42 per cent of the vote, an increase of five per cent on the 2015 result, but none the less lost 13 seats suggests that the blue vote was inefficiently spread.

But it is very hard to believe that campaigning deficiencies were responsible for the bulk of the problems.  A more natural explanation is the obvious one.  As Stephen Bush pointed out during the campaign, the polls did not go “all over the place” during it.  “When you look beneath the headline figures, the polling companies are telling us very similar stories,” he wrote. “The big difference is how the two groups of pollsters weight votes….one of the big methodological changes that the various polling companies made after the disaster of 2015 was to change how they assessed turnout”.

We know now that the YouGov/Survation/Opinium position that Bush described – which built in a higher turnout by younger voters than other polling operations – turned out to be right on the day.  But regardless of the polls’ different findings and assumptions they all told, as he said, the same story of relative Tory decline and Labour advance.  And what seems to have propelled that advance and decline was the two parties’ manifestos.

Labour formally launched theirs after an earlier leak on May 16.  Its three nearest Survation poll ratings to the launch before it took place showed the party at 29, 30 and 20 per cent.  Its three nearest afterwards were 34, 34 and 37 per cent.  These totals were then followed by ratings of 39, 40, 40, 45, 45 and 41 per cent.  As we noted at the time, Labour’s manifesto had a retail offer for voters, and it was able to build an increasingly successful campaign on the back of it.

The Conservatives launched their manifesto on May 18.  Its three nearest Survation poll ratings to the launch before it took place showed the party at 40, 47 and 48 per cent.  Its three nearest afterwards were 43, 46 and 43 per cent. These totals were then followed by ratings of 40, 41, 41, 39, 42 and 42 per cent.  As we wrote in that same article, the Conservative manifesto did not have a retail offer for voters.  Neither it not a concentrated assault on Labour’s ever came.  “The low point of the Conservative campaign so far [has] followed the manifesto launch,” we wrote. “The social care policy tanked, and Tory poll ratings fell with it.”

In summary, David Davis and others were not necessary wrong to push for an early election – which, as May’s local election results suggested, was winnable, along with an increase in the Conservative majority.  The full story of the 2017 election is not yet told.  But a provisional conclusion must be that while CCHQ’s failures made the difference between gaining a bare majority and not doing so, it was the manifesto, and its aftermath, which destroyed the prospect of more Tory seats, let alone a landslide.