The Liberal Democrats have been accused of using misleading data on campaign literature to suggest they are polling ahead of other parties in certain constituencies.
It comes as the party president, Baroness Brinton, was forced to apologise on air for another leaflet that attributed quotes by leader Jo Swinson to The Guardian.
Confirming the party is reviewing its campaign literature, she told Good Morning Britain: “I’m sorry. That was human error... Somebody had cropped out the reference.”
In the latest incident, data from independent polling company Flavible has been cited on general election material released by the party's local offices - but it has been criticised for conflating national polling with constituency projections.
The row emerged over leaflets distributed in Putney which claimed a Flavible projection of a "Yougov" poll showed the Lib Dems neck-and-neck with the Conservative Party, with both polling at 31%.
The Labour Party is shown as polling at 18%, with the leaflets telling residents Labour "can't win here", even though the Lib Dem candidate came a distant third in the 2017 general election.
Flavible's founder said the Lib Dems - who last week were accused of publishing another misleading poll - had "mislabelled" the data while a senior YouGov director said the poll "shouldn't be represented as YouGov’s".
Flavible, which is not a member of the British Polling Council association of pollsters, takes YouGov's national results and uses it alongside population data to project how a given seat may vote - something that some experts say cannot be reliably done.
George Rushton, Flavible's founder, said the party has "themselves misinterpreted the data or intentionally mislabelled the data for political advantage”.
Mr Rushton, a software developer, urged parties not to use the data on hard copy campaign literature as the demographic data changes, and so do the projections.
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He said: "I expect a recall or deletion of any and all uses that can be thought of this way along with a correction from those involved.
"I do not think a single projection of a single seat based on a single poll is acceptable as campaign literature and thus I would completely advise against its use in this way.”
He said he has contacted individuals, local representatives and organisations in private and, while some have amended or removed the data, some "have not replied at all”.
Responding to users on Twitter, YouGov's director of political research, Anthony Wells, confirmed the constituency projection cited by the Lib Dems had not been done by his company.
He said: "We haven't done a constituency poll of Putney.
"It's a projection from a website called Flavible, based on one of our GB polls.
"The projection is Flavible's, it shouldn't be represented as YouGov’s."
According to its website, Flavible offers publicly available "in-depth seat projections" based on polls released by the top polling companies, and Mr Rushton said his firm "does not supply any data to any political party or individual”.
The UK's independent fact-checking charity, Full Fact, said: "Flavible's stated methodology is a 'weighted swing', whereby changes in support for the parties at the national level are applied to each constituency, with the numbers weighted by things like which way the seat voted in the Brexit referendum and whether it changed hands in either of the last two elections.
"The evidence suggests that this does not always yield reliable results.”
A Liberal Democrat spokesman said: "Flavible projections are not and will not be used on national campaigns.”
The Lib Dems have also been accused of quoting incorrect statistics in Chelmsford and distorting the scale of their graphs in Durham.
Election literature distributed in Bath and Somerset shows the Liberal Democrats polling at 32%, just behind the Conservatives' 38% and far ahead of Labour's 8%.
However, the small print on the data shows that only 405 people were surveyed and asked the question: "Imagine that the result in your constituency was expected to be very close between the Conservative and Liberal Democrat candidate, and none of the other parties were competitive.
"In this scenario, which party would you vote for?’"
The data was called "misleading and sleight of hand" by SNP MSP James Dornan.