SOCIAL media platforms should comply with a compulsory code of ethics overseen by an independent regulator to tackle harmful or illegal content on their sites, a Commons committee has demanded.

In a major report, MPs warned that democracy is at risk from the “malicious and relentless” targeting of citizens with disinformation and adverts from unidentifiable sources, as they called for reform to electoral communication laws.

The Digital, Culture, Media and Sport Committee said ethics guidelines are needed to set out what is and what is not acceptable on social media, including harmful and illegal content that has been referred to the platforms by users or identified by the companies.

If tech companies fail to meet their obligations under the code, then an independent regulator should be able to launch legal proceedings against them and have the power to issue large fines, the MPs said.

They wrote: “Social media companies cannot hide behind the claim of being merely a ‘platform’ and maintain that they have no responsibility themselves in regulating the content of their sites.”

The report also rounded on Facebook chief Mark Zuckerberg, who was accused of showing “contempt” towards the committee by choosing not to appear before it last year.

They said the social networking site did not seem willing to be regulated or scrutinised, and claimed its “opaque” structure seemed to be designed to “conceal knowledge of and responsibility for specific decisions”.

In the last year, Facebook has come under intense pressure over some of its business practices, following the Cambridge Analytica scandal, a series of data breaches and concerns over fake news and other content on the site.

Tory MP and committee chairman Damian Collins said: “The big tech companies are failing in the duty of care they owe to their users to act against harmful content, and to respect their data privacy rights.”

The committee’s final report into disinformation and fake news also said electoral law was “not fit for purpose” and should be updated to reflect the move to “micro-targeted” online political campaigning.

They called for a comprehensive review of the current rules and regulations surrounding political work during elections and referenda, and separately urged the Government to put pressure on social media companies to publicise instances of disinformation.

Ministers were also asked to reveal how many investigations are being carried out into Russian interference in UK politics.

The Government is expected to publish a white paper later this year on proposals to reform laws to make the internet and social media safer.

An Electoral Commission spokesman added: “We agree that reform of electoral law is urgently needed. The UK’s Governments must ensure that the tools used to regulate political campaigning online continue to be fit for purpose in a digital age.

“Requiring digital adverts that seek to target voters to state clearly who is responsible for them would be an important first step.”