Boris Johnson still ahead in the polls - but by how much?

It may have been one of the most turbulent weeks endured by a prime minister in modern Westminster history, but polling suggests Boris Johnson remains on top – with one important caveat: nobody can agree by how much.

A crop of polls taken at the end of last week – during which the prime minister was defeated in the Commons and lost the support of his own brother, Jo, left the Conservatives anywhere between three and 14 points ahead of Labour.

That would leave Johnson somewhere between a landslide and a hung parliament similar to today’s with the Conservatives as the largest party, although such is the current volatility that it is acknowledged that public opinion can easily shift.

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But while there is a healthy scepticism about the value of polls, not least because the unexpected outcome of the 2015 and 2017 elections, they underpin political and media thinking, not least because they are simple and memorable.

“Polls are the one of the only things we have to illuminate public opinion,” said Deborah Mattinson, the founder of market research firm Britain Thinks. “We love them, partly because we use them to confirm what we already thought.”

The simple reason why Johnson and so many Conservatives want an election is that the polls say they their party will win – current averages have Johnson’s party ahead by nine points. Many Labour MPs are nervous and want to push an election beyond Johnson’s 31 October deadline in the hope he will be damaged.

But it is not clear if these assumptions are well founded. On Monday, Jason Stein, an aide to Amber Rudd, a former cabinet minister, said private polling done on behalf of Downing Street and revealed to special advisers had suggested the Conservatives would end up with 295 to 300 seats, well short of the 326 required for a majority.

Others have a different recollection of an internal discussion in the middle of last week, where Dominic Cummings, Johnson’s strategy adviser, was asked about the risk of the Conservatives losing 30 or 35 seats in London, Scotland and the south-west. What they remembered was that Cummings “shrugged his shoulders” and offered no immediate rebuttal to the gathered group.

Pollsters say they have standardised on the question they ask: “Which party would you vote for in a general election held tomorrow?” and include Nigel Farage’s relatively new Brexit party in the prompted list that follows. Online polling has become dominant, with firms recognising that it is no longer possible to obtain a representative sample from people who pick up a telephone.

Yet all pollsters make adjustments to weight their samples. Some of this is uncontroversial, to match up with UK averages for age, gender and social class, but for political work this can take in previous voting patterns, how people voted in the 2016 referendum and their overall level of interest.

“The industry has a real problem measuring turnout, people who say they will vote but do not do so in the end,” said Joe Twyman, a founder of Deltapoll, a market research firm. “This time that could present a real problem tracking Labour leavers and Conservative remainers, those left behind by their parties.”

One response from pollsters is to develop so called multilevel regression and post-stratification models, known as MRP polls. They seek to create a model result for every single UK constituency, theoretically producing a more accurate outcome.

MRP models, however, require large sample sizes of 10,000 plus to produce sufficient local data, compared with normal polling samples of 1,000 or perhaps 2,000, making them expensive to commission. They too, are also vulnerable to assumptions, Twyman acknowledges.

Political actors also repeatedly deploy narratives about polling to further their position. The People’s Vote campaign argues that Labour and Conservative MPs should back a second referendum as an alternative because, such are the uncertainties about polling that, in the words of a spokesman, “at no point will enough MPs feel confident enough they can win to trigger an election”.

A further complication for any forthcoming election is who will stand in each seat, amid talk of a range of pacts. Nigel Farage has talked up the idea of various election pacts with the Conservatives although his ultimate intention remains unclear.

Discussions continue about a range of pro-remain deals, although these can been difficult to pull off. With 22 Tories having recently lost the whip there could yet be other independent candidates, such as Rudd or the ex-chancellor Philip Hammond.

Yet, curiously, when Deltapoll asked voters if the ex-Tory MPs were to form “a moderate one nation Conservative party”, the lead for Boris Johnson over Labour extended from three to 12 points, according to the pollster.

The prime minster’s Tories received 35% to the “Hammondites” 9%, with Labour on 23% and the Lib Dems on 14%. It is only one poll, but it shows how difficult it is to make predictions in the current climate.