A campaign group is calling for fact-checking of political advertising to be a legal requirement after what it describes as a "fake news and disinformation general election".
The Coalition for Reform in Political Advertising says at least 31 campaigns from across the party spectrum have been indecent, dishonest or untruthful.
The non-partisan body is made up of advertising professionals.
It says the next government must create a new regulator to oversee the matter.
The organisation also suggests 87% of voters think there needs to be a law to compel political-ad creators to make only truthful claims.
The figure is based on a survey of 1,691 adults conducted by YouGov on the Coalition's behalf.
The Coalition says the largely unregulated world of election ads bears little resemblance to one of the founding principles of retail advertising, namely that ads should be "legal, decent, honest and truthful".
Since the start of the election campaign, a team of 10 volunteers from the campaign group sifted through social media ad libraries, party timelines and physical party leaflets.
It picked out examples of material the volunteers thought were problematic and then cross-referenced the claims with the work of fact-checking organisations.
It then collated an example list of 31 separate items judged to transgress the code of commercial marketing.
- a Conservative Party tweet that featured a video of Labour's Keir Starmer, in which his replies to questions about Brexit had been edited out. The Coalition said this was "misleading"
- a Liberal Democrat post featuring a bar chart putting the Lib Dems in second place to the Conservatives, but no information as to whether the underlying data came from polls or earlier election results. Without this the results were not "meaningful" said the Coalition
- a Brexit Party ad that said five million Labour voters had voted to leave the EU. The Coalition noted that "precise figures do not exist", adding that most estimates put the number at between three to four million
- a Labour Party post that said a sell-out deal with Donald Trump could mean giving £500m a week to big drugs companies. The Coalition said the sum was a "rough calculation" based on a "fairly extreme scenario"
The group said the examples that it had highlighted - which included both paid and unpaid ads, most online but some offline - should not be regarded as being comprehensive, meaning there were likely to be other cases it had not spotted.
Ads in the UK are regulated by the Advertising Standards Authority. Its rules prohibit misleading information and require advertisers to have "documentary evidence" to support their claims.
But political advertising is regulated outside of the ASA. And the electoral law that applies "doesn't require claims in political campaigns to be truthful or factually accurate," according to the House of Commons library.
Coalition for Reform in Political Advertising co-founder Alex Tait says its report demonstrated there is "a very significant problem".
This is the first general election since several of the tech giants gave the public access to databases listing the political ads running on their platforms.
At least £2m has been spent on Facebook and Instagram over the last 30 days, and an advertising blitz is expected over the last 48 hours of campaigning.
Many of the ads have not contained misleading claims, but the issue has also been addressed in a separate study by the non-profit organisation First Draft published on 6 December.
It looked just at every paid-for Facebook ad from the three main UK-wide parties run over the first four days of December:
- for the Conservatives, it said that 88% (5,952) of the party's most widely promoted ads either featured claims which had been flagged by independent fact-checking organisations (including BBC Reality Check) as not correct or not entirely correct. The figure includes instances of the same claims being made across multiple posts. One example was that Labour would spend £1.2 trillion at a cost of £2,400 to every household, which was contained within 4,028 ads. Those sums are significantly higher than others' analysis of Labour's plans
- for the Lib Dems, it said hundreds of potentially misleading ads had featured identical unlabelled graphs, with no indication of the source data, to claim it was the only party that could beat either Labour, the Conservatives or the SNP "in seats like yours"
- For Labour, it initially said that it could not find any misleading claims in ads run over the four-day period. Subsequently, First Draft issued an update, saying a bug in Facebook's ad library meant their analysis was missing some data. In fact, according to their methodology, 7% of ads published by Labour over that time contained inaccurate or misleading claims. Again, this is only over a four-day period and does not necessarily represent the whole campaign
Labour's supporters have been more likely to share unpaid-for electioneering posts than supporters of other parties.
And among the most interacted-with posts of the campaign was Jeremy Corbyn's tweet containing the disputed figure of £500m in relation to the NHS.
Concerns are not limited to online content.
In particular, one expert has flagged the distribution of political campaign materials designed to look like local newspapers.
Dr Claire Hardaker says although this is a tried-and-tested technique, it can have a damaging effect on democracy.
"Local papers are seen as more honest, impartial, talking to me specifically," explained the Lancaster University academic, who researches deceptive and manipulative language.
"They are an objective voice who care about you. When political parties borrow this voice, people interpret what they're saying in a different way, seeing them as more credible."
UPDATE: This piece was published on 10 December 2019 and has been updated to include an revision by First Draft News of its research findings.