Facebook has quietly rescinded a policy banning false claims in advertising, creating a specific exemption that leaves political adverts unconstrained regarding how they could mislead or deceive, as a potential general election looms in the UK.

The social network had previously banned adverts containing “deceptive, false or misleading content”, a much stronger restriction than its general rules around Facebook posts. But, as reported by the journalist Judd Legum, in the last week the rules have narrowed considerably, only banning adverts that “include claims debunked by third-party fact-checkers, or, in certain circumstances, claims debunked by organisations with particular expertise”.

Under Facebook’s third-party fact-checking programme, it invites independent organisations such as the UK’s Full Fact to verify claims posted to the social network. But the groups, made up mainly of small charities and nonprofits, are heavily constrained in how many claims they can fact-check, meaning they often only verify the most viral cases.

But even that limit has been lifted for some political adverts. A separate policy introduced by the social network recently declared opinion pieces and satire ineligible for verification, including any website or page “with the primary purpose of expressing the opinion or agenda of a political figure”. The end result is that any direct statement from a candidate or campaign cannot be fact-checked and so is automatically exempted from policies designed to prevent misinformation. (After the publication of this story, Facebook clarified that only politicians currently in office or running for office, and political parties, are exempt: other political adverts still need to be true.)

The changes, Legum reported, followed a run of Donald Trump adverts that contained false claims but were not removed under the old rules.

The new rules could prompt a clash between Facebook and UK regulators. The Advertising Standards Authority does not cover political adverts in Britain, the content of which is largely unregulated, but it does cover all other adverts, including those posted on Facebook. The ASA’s code explicitly bans adverts that “materially mislead or [are] likely to do so”, language that is close to that used in Facebook’s previous policies.

A Facebook spokesman said: “We don’t believe that it’s an appropriate role for us to referee political debates. Nor do we think it would be appropriate to prevent a politician’s speech from reaching its audience and being subject to public debate and scrutiny.”

Facebook’s decision comes as the rival service TikTok takes the opposite stance. In a blogpost, the social network, whose reported 500 million users would make it the largest in the world not owned by Facebook, made clear it would not be hosting any political adverts.

Q&A What is TikTok? Show TikTok is a video-sharing app which has become phenomenally popular with teenagers. Users film themselves in 15-second clips, typically set to music, and upload them to be viewed by followers and strangers alike. It has been the No 1 app on the worldwide App Store for five consecutive quarters, with an estimated 500 million users worldwide. Owned by Chinese startup ByteDance, the app as it is today is a merger of the original TikTok, which was launched internationally in September 2017, and the viral sensation Musical.ly. The latter had already become one of the most popular social media platforms for UK and US teenagers by the time it was purchased by ByteDance in November 2017. The merger meant TikTok ended up on the smartphones of more than 60 million users overnight. Bytedance has a valuation of $75bn (£60bn), based primarily on the extraordinary growth of TikTok and its Chinese equivalent, Douyin. Lil Nas X found fame overnight when his track Old Town Road was used extensively on 15-second clips on the social network. That enthusiasm took the artist to a record-breaking run at the top of the US Billboard Hot 100 chart. However, Bytedance was fined a record $5.7m in the US for illegally collecting personal information from children under 13, and has been under investigation in the UK for how it handles the personal data of its young users, and whether it prioritises the safety of children on its social network. Alex Hern, UK technology editor

“Any paid ads that come into the community need to fit the standards for our platform, and the nature of paid political ads is not something we believe fits the TikTok platform experience,” wrote Blake Chandlee, the company’s vice-president of global business solutions. “To that end, we will not allow paid ads that promote or oppose a candidate, current leader, political party or group, or issue at the federal, state, or local level – including election-related ads, advocacy ads, or issue ads.”

Chandlee said the decision was prompted by TikTok’s mission “to inspire creativity and build joy”. That same rationale had been cited by the company, which is owned by the Chinese startup Bytedance, to explain why it censored posts that went against the political orthodoxy of Beijing, mentioning topics such as the Tiananmen Square killings or the independence movement in Taiwan.

When the Guardian revealed the censorship, TikTok said the rules had since been repealed and replaced with ones that “take localised approaches” to “provide an app experience that fosters their creativity”.