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.

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 “microtargeted” 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.

Tory MP and committee chairman Damian Collins said: “Democracy is at risk from the malicious and relentless targeting of citizens with disinformation and personalised ‘dark adverts’ from unidentifiable sources, delivered through the major social media platforms we use every day. Much of this is directed from agencies working in foreign countries, including Russia.

“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.

“Companies like Facebook exercise massive market power which enables them to make money by bullying the smaller technology companies and developers who rely on this platform to reach their customers.

“These are issues that the major tech companies are well aware of, yet continually fail to address. The guiding principle of the ‘move fast and break things’ culture often seems to be that it is better to apologise than ask permission.

“We need a radical shift in the balance of power between the platforms and the people. The age of inadequate self-regulation must come to an end. The rights of the citizen need to be established in statute, by requiring the tech companies to adhere to a code of conduct written into law by Parliament, and overseen by an independent regulator.”

Shadow culture secretary Tom Watson said: “Labour agrees with the committee’s ultimate conclusion: the era of self-regulation for tech companies must end immediately. We need new independent regulation with a tough powers and sanctions regime to curb the worst excesses of surveillance capitalism and the forces trying to use technology to subvert our democracy.

“Few individuals have shown contempt for our parliamentary democracy in the way Mark Zuckerberg has. If one thing is uniting politicians of all colours during this difficult time for our country, it is our determination to bring him and his company into line.”

A Government spokesman said: “The Government’s forthcoming White Paper on Online Harms will set out a new framework for ensuring disinformation is tackled effectively, while respecting freedom of expression and promoting innovation.

“This week the Culture Secretary will travel to the United States to meet with tech giants including Google, Facebook, Twitter and Apple to discuss many of these issues.

“We welcome this report’s contribution towards our work to tackle the increasing threat of disinformation and to make the UK the safest place to be online. We will respond in due course.”

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. We also welcome their call for us to have additional and extended powers in order to more police electoral law, including a substantial increase to our current maximum fine limit.”

Elizabeth Denham, the Information Commissioner said: “The DCMS inquiry has been vital to understanding the increasingly complex era of digital political campaigning, big data and disinformation online and we have welcomed the opportunity to contribute to it.

“We’re pleased with the committee’s support of our recommendation for a statutory code that will clarify how personal data should be used during political campaigning. The ICO’s investigations into these areas continue and we’ll be reviewing the full report with interest.”