The decision by Twitter’s chief executive, Jack Dorsey, to “stop all political advertising on Twitter globally” was the right thing to do at the right time. There is understandable queasiness about paid-for political reach enabled by “highly optimized and targeted” messaging whose extent and spread is largely unknown and unregulated. When two of the world’s most advanced democracies – the United States and the United Kingdom – have been undermined by the flood of prejudice and falsehood on social media, it is heartening that Mr Dorsey has acted. It should worry us all that politicians and the social media giant Facebook have not.

In Britain electoral law is, according to parliament’s public administration and constitutional affairs committee, in an “archaic and confusing state” that requires deep reform. MPs said there were plans for digital imprints showing who has produced online ads, and called for a wider review of digital campaigning in the UK. However, such welcome pledges are easier to make than to keep. They echo similar calls by the Electoral Commission after the 2016 Brexit referendum, the Law Commission before that, and also in Boris Johnson’s now-defunct Queen’s speech. Fine words, but nothing has happened. Dishonest campaigning, opaque data harvesting and dark political advertising all flourish.

Mr Dorsey’s message is being warmly received, which ought to perhaps worry his real target: Facebook. Mark Zuckerberg, Facebook’s founder, casts his company as part of a “fifth estate … a new kind of force in the world” which gives the public a megaphone to “express themselves at scale (online)”.

There’s evidence that social media adverts help unknown candidates to stand out. It is also the case that nontraditional candidates would find it harder to break through without Facebook. WhatsApp, which is owned by Facebook, has also defended activists across the world from sophisticated cyber-attacks. However, Mr Zuckerberg confuses freedom of expression with freedom of paid intensification and dilation of that expression – which favours the rich.

Facebook’s power over what users see gives it potential for immense influence on politics. Foreign and domestic actors have long realised this and pushed misinformation and division. Facebook has created rules for itself that are quixotic and confused. The company will not police politicians’ posts – including any containing false and misleading claims – but will decide, it seems, whether an individual is a politician or not. Mr Zuckerberg is on shaky ground and the quicker he realises this the better.

Facebook is worth about half a trillion dollars. It sucks up four-fifths of global social networking revenue. In the US, Democrat senator Elizabeth Warren is quite right to say that the company has “too much power over our economy, our society and our democracy”. It does need to be broken up. However, even if this were attempted it would likely be a lengthy process. In the UK, the worry is that politicians understand that the integrity of elections can be undermined by Facebook, but political leaders are reluctant to clamp down as they benefit from it.

There are some simple things that could be done: forcing Facebook to reveal where parties are spending campaign cash and enforcing constituency spending limits would be a start. An official study of advertising in social media is urgently needed. Campaigners have to be able to be held to account. They cannot operate in the dark. That means subjecting their political activities, and the companies that give them this voice online, to effective regulatory oversight.