Tory poll leads don’t account for potential Remainer tactical voting by the "Hugh Grant voter", who is willing to put their cross next to either Labour or the Liberal Democrats, depending on their constituency, in order to prevent a Johnson victory.

One senior Conservative told BuzzFeed News they were surprised that more pro-Remain politicians had not focussed on encouraging tactical voting in order to bring about a hung Parliament, saying they expected a further move to be made on that front in the final week.

“No doubt Gordon Brown will make his traditional pre–polling day intervention. But if you had Tony Blair, Tom Watson, Keir Starmer, Vince Cable, et al., calling for tactical voting to stop Brexit, that could dominate the final days,” they warned.

Some Tories have questioned the wisdom of Brexit-centered messaging from the Johnson campaign in the last week, in case it has the effect of focussing Remain voters’ minds and encouraging them to vote tactically.

Speak to Tory campaign officials about what they think is going to happen and most fall into one of two camps. Some who were more nervous two weeks ago are now bullish that Johnson will secure a sizable majority of over 40 seats.

One reason for the renewed confidence is early indications from postal votes in "Red Wall" Tory target seats in the North. Postal voting is not supposed to leak, but at every election, there is informed speculation from local officials that often changes the way parties campaign in the final days.

A message sent by a Labour official in the north to colleagues last week, seen by BuzzFeed News, stated that “postal votes in all Labour seats are bad” and ordered activists to stay in so-called defensive seats already held by the party, rather than head to “offensive” target seats held by Tories.

Conservative Campaign Headquarters (CCHQ) believes that the recent narrowing of the polls over the last week can be explained largely by Lib Dem voters moving to Labour in London, where the party is already well ahead, rather than Tory voters moving to Labour in key marginals.

Tory aides are also immensely relieved that Johnson managed to navigate the TV debates and the rest of the campaign — so far — without committing a significant gaffe. “May had ‘nothing has changed’, Cameron got his football team wrong, but Boris is better than you think at holding the line,” an adviser said. The visit of US president Donald Trump went off without any major clangers, with the Tories again counting their luck.

CCHQ will spend the run-up to the election in “robo-mode”, repeating the same arguments again and again in the form of a “closing statement” at a trial. It has spent a vast amount of money buying the top advertising spot on YouTube on Saturday so every UK visitor to the site sees the latest Tory campaign advert. The ad buy was not micro-targeted and instead is a massive blanket buy — part of a huge final-week social media spending blitz straight out of the Vote Leave playbook.