Election leaflets are providing “grotesque” information about how to vote tactically in the May elections, using national polling data, “dodgy” bar charts and doorstep surveys to support claims about parties’ chances of winning.

Leaflets distributed by local politicians across England are claiming that either only their party can win, or another party “can’t win here” when “there is no good evidence to show that’s true”, a Full Fact investigation for the Guardian has revealed.

Some of the campaigning material Full Fact looked at that contained a chart or graphic “failed to provide reliable evidence to back up a specific claim about how people are likely to vote locally, or were unsourced or misleading in some other way”, with examples from all the major parties.

Readers who responded to a Guardian callout shared images of leaflets they had received. Some noted that they had at first thought a leaflet from the Conservatives was from the Green party, because it was printed in green with only a small Conservative logo.

Another expressed doubt about what they described as “very dubious” statistics from the Liberal Democrats showing a party was “the only sensible way to vote”.

The polling and political analyst Peter Kellner, the former chair of YouGov, described some of the claims and data used in leaflets as “grotesque” and said that spurious claims backed up by unreliable data were becoming increasingly common.

“Because there are far more parties, and it is far less clear who you should vote for if you want to vote tactically, all parties are putting a lot of effort into convincing voters that they are the only option,” he said. “But if commercial companies were making some of these claims they wouldn’t be allowed to get away with it.”

Full Fact said good data on voting intentions was often not available in local elections and that it was reasonable for political parties to address significant swings in the national polls. But the organisation concluded that “some of these leaflets could mislead people as they choose how to vote, for instance by claiming definitively that another party ‘can’t win here’, or that only one party can stop another”.

“There’s nothing wrong with parties making a case to voters, but too many leaflets are making overblown, dodgy claims with cherrypicked, misleading or unreliable data,” said the Full Fact editor, Steve Nowottny.

The organisation analysed 331 leaflets from across England uploaded to Democracy Club’s online archive in the first two weeks of April. Fifty-nine included a chart or graphic, with 14 of these unsourced or misleading or failing to provide reliable evidence about voting intention.

Some of the most egregious examples uncovered in the leaflet analysis include a Labour leaflet distributed in Ealing Common, a ward in Ealing, west London, which warns voters not to “let Reform sneak in here” alongside a bar chart which states “Greens can’t win here”, with the addition of an arrow pointing to the green bar on the chart stating: “Wasted vote!” The Lib Dems, who currently control two of Ealing Common’s three seats, are the smallest bar.

The chart uses the 2024 London assembly result for Ealing and Hillingdon, a much larger area. It also adds an extra bar which appears to add Reform national polling “giving a picture that is both misleading and confusing” according to Full Fact. “What they’ve done is grotesque, and they’ve not been candid,” said Kellner. “The figures are in no sense indicative of Ealing Common.”

Ealing Labour party said the diagram was “clearly an illustration of what could happen in a very competitive election, and can’t be taken literally, as no element of trying to predict the future can be”. It conveyed “the very real and serious point that Reform are attempting to make real gains in Ealing”, and was “a common method of trying to make that point during an election campaign”, it said.

A leaflet from the Green party in Gateshead shows Reform in the lead with the Greens in second, beneath a headline that says the “Greens are now the only alternative to Reform”.

The chart states it is based on opinion poll data from YouGov in March, but the same poll currently puts the Greens third. Regardless, a national poll was not a reliable indicator of local outcomes, said Kellner.

A Reform leaflet from Chelmsford gives no source for its bar chart which puts Farage’s party on 34%, and the Conservatives and Labour on 16%. Full Fact said while Reform had polled at 34% with at least one pollster in the past, it had not found an exact match with the Conservative and Labour figures at the same time.

The bar chart was also “completely out of proportion”, it said. An online calibration tool suggests that if the Reform bar represents 34%, the height of the Labour and Conservative bars puts them at about 9%, not 16%. “This is obviously misleading about the numbers themselves, whether or not they’re accurate or relevant,” said Full Fact.

A “strange” Liberal Democrat leaflet from from Eastgate and Moreton Hall in Suffolk states: “It’s Lib Dem or Reform here,” while using a bar chart showing the Conservatives in second and the Lib Dems in third.

It also uses a YouGov quote stating the Lib Dems are “most likely to see off Reform UK”, probably a reference to a YouGov article from March 2025, which asked voters which party they would vote for if only Reform and the Lib Dems had a chance of winning. The Liberal Democrat candidate’s agent said: “The image is illustrative and not a true graph as such, which we emphasised by not putting in any indices.”

Meanwhile, a leaflet from the Conservatives in Haslemere, a ward in west Surrey, tells voters “Reform can’t win here”, apparently based on data for the whole of Surrey from the 2024 general election, which Full Fact said was “very unreliable evidence”.

Full Fact said the assessment of leaflets was not intended to be fully representative of the national picture, but instead to assess what voters might understand from the information given, and whether it included reliable evidence.

Kellner said that while “the mechanics of democracy work reasonably well” in the UK, disinformation peddled by political parties were a “small part of a larger jigsaw” that had seen trust in politics, politicians and institutions more widely eroded in the past two decades. “If one defines a healthy democracy as one where there is an open, free exchange of views and information which allows voters to make up their minds on the basis of truth rather than lies, then, yes, this is bad for democracy,” he said.