Party defends claims that it is now competitive in seats where it came third in 2017

Attempting to mislead voters by using polling data to claim electoral advantage over rivals could have long-term implications for trust in politicians, a fact-checking charity has warned.

Leaflets sent to the Guardian from readers around the country show the Liberal Democrats in particular appear to be using bar charts to press home a message that they have a good chance of winning, even in seats where the likes of the Tory Jacob Rees-Mogg or Labour stalwarts are seen as difficult to dislodge.

In some leaflets the party omitted spectacular results for the Brexit party in bar charts showing the European election results, while in others it projected local election results to forecast wins in the general election.

The chief executive of the independent fact-checking charity Full Fact, Will Moy, said dubious use of data would damage the future trust of voters.

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“Honesty in politics matters, whether it’s in a speech or in a leaflet. It’s misleading to present a mix of data from different polls and constituency boundaries as an accurate predictor of local results this December,” he said. “Parliamentary candidates are asking voters for their trust over the next five years. The words of our future MPs shouldn’t be undermined by misleading use of graphs or polls.”

From Totnes to Wimbledon, Oxford and Warwick, the Liberal Democrats have used phone surveys and local, district and European elections data to try to convince voters of their ability to win.

The muddling of data for electoral advantage was a “perennial problem” and practised by all parties, including the Tories who recently claimed Labour party plans would cost £1.2tn, said the psephologist John Curtice.

“In 75 constituencies where the Lib Dems came third last time, the European election projections would put them in second place. The Lib Dems always suffer from the potential perception ‘we can’t possibly win’ and that’s why they are using the European elections, because they need to give the impression they can win,” he said.

Lib Dem leaflets in Totnes enraged some voters. Photograph: Lib Dems

In Totnes, where the Lib Dem candidate is the former Tory Sarah Wollaston, the party’s leaflets declare the election is “so close” that “only the Liberal Democrats can beat the Tories”. In 2017, the Conservatives were clear winners with 53.7% of the vote, and Labour, not the Liberal Democrats, came second.

One reader who contacted the Guardian said he had initially assumed the Totnes bar chart was from the last general election. “I suppose I can be criticised for this … but when I read the caption, I saw it was for the district election, an election completely unlike this one,” said Stuart Allen.

“I consider this very low skulduggery, and in fact the sentence in the Lib Dem leaflet which says ‘the results … show only the Lib Dems can beat the Tories’ to be a downright lie. I’m fuming and, incidentally, very unlikely to vote Lib Dem now.”

Leaflets sent to the Guardian show similar tactics countrywide. In Wimbledon in London the party leaflet claims “elections here are always a clear choice between Lib Dems and the Tories” when in the last two general elections the party came third.

BathNES Lib Dems 🔶 (@bathnesld) If we work together, and back @nickcoatesnes we will beat Jacob Rees-Mogg in North East Somerset #VoteNickCoates #StopMogg pic.twitter.com/ymubNsMVg8

In Jacob Rees-Mogg’s constituency of North East Somerset, the party used a Survation poll to suggest it will be able to oust the hardline Brexiter.

Facebook Twitter Pinterest Lib Dem bar chart suggests it can oust Jacob Rees-Mogg. Photograph: Twitter

On closer inspection, the poll is based on the question: “Imagine that the result in your constituency was expected to be very close between the Conservative and the Liberal Democrat candidate, and none of the other parties were competitive. In this scenario, which party would you vote for?”

One reader described it as “irresponsible manipulation” as the last general election result put the Tories at 53.6%, Labour at 34.7% and the Liberal Democrats at 8.3%.

Facebook Twitter Pinterest Oxford East is a Labour stronghold, but not according to a Lib Dem bar chart. Photograph: Lib Dems East Oxford

Oxford East was a Labour stronghold in 2017 with 65% voter share. But a Lib Dem bar chart shows Labour on 37%, the Lib Dems on 35%, the Conservatives on 10% and the Greens on 9%. Data is sourced as a “projection for Oxford East constituency, Flavible Politics, YouGov poll 20 Sept 2019”. The party has already been criticised for using data from Flavible as it is not a member of the British Polling Council.

The Lib Dems made similar claims based on single polls in other constituencies including Bristol North West and the Cities of London and Westminster, where the former Labour MP Chuka Umunna is running.

Facebook Twitter Pinterest A Lib Dem leaflet from Cities of London and Westminster. Photograph: Lib Dems

Lib Dem literature says the party is first in the seat, when it came third in 2017. The bar chart is sourced to a projection by Flavible based on a single day’s polling.

In a statement, the Flavible founder, George Rushton, distanced himself from such use of its data, saying he did “not think a single projection of a single seat based on a single poll is acceptable as campaign literature”.

Anthony Wells, the director of political research at YouGov, which has also been cited as a source of Lib Dem data, said it did not do constituency polls and while it did produce constituency projections it had “not yet published any for the 2019 election campaign”.

Facebook Twitter Pinterest A Lib Dem leaflet in Warwick omits the Brexit party. Photograph: Lib Dems

A spokeswoman for the Lib Dems defended their tactics: “Every complaint about a Lib Dem leaflet shows that Labour and the Tories are in denial about the fact that things have changed massively since 2017.”

“Since then, the Lib Dem national share of the vote has more than doubled, and we finished ahead of both Labour and the Tories in the European elections. We’ve had tens of thousands of new members and seven new MPs join us as the strongest remain party.

“We are now genuinely competitive in a significant number of seats – including many very strongly remain-voting areas – where we were in third place in 2017,” she said.