Twitter's global ban on political advertising takes effect from Friday 22 November. 

It prevents anyone paying to promote any content on the social media platform that refers to candidates, political parties, government officials, elections, referendums, ballot measures, legislation, regulations, directives, or judicial outcomes.

Announcing the move last month, CEO Jack Dorsey tweeted: "We believe political message reach should be earned, not bought."

How much impact could it have?

Twitter's move goes further than most other platforms but its overall impact may be limited: The social media platform claims 330 million daily active users, but says fewer than half of those – 145 million – see adverts. 

Twitter is also small compared with other web giants such as Facebook and Google, which both still allow political advertising. Recent figures suggest it is only the 12th largest social media platform in the world.

Twitter isn't the only social media platform to ban political adverts altogether. Chinese-owned video-sharing site Tik Tok recently announced it wouldn't allow them.

Unlike teen-oriented Tiktok and many other sites, Twitter is part of the daily political conversation, at least in the US, UK and Japan, to an extent that isn't true of other sites. It is, after all, US President Donald Trump's platform of choice. 

However, the ban only prevents anyone buying content. It does nothing to stop sharp practice or fakery of the sort that has caused controversy in the current UK election, when for example, the Conservative Party rebranded its Twitter feed as 'FactcheckUK' for several hours to attack Labour leader Jeremy Corbyn during a televised debate.

Twitter condemned the Conservative move and threatened "decisive corrective action," if it happened again, but some of the material still appears in the Conservative feed.        

The episode amounted to an ironic inversion of statements by successive Google bosses that tech platforms shouldn't be regulated by politicians because they "move faster than governments." Politicians can themselves take advantage of the lack of regulation, leaving tech companies flatfooted, as Twitter's Jack Dorsey implicitly recognized when he said machine learning-based optimization of messaging, micro-targeting, unchecked misleading information, and deep fakes present new challenges, 

 "All at increasing velocity, sophistication, and overwhelming scale."

The Conservative campaign has been getting input from PR firm Topham Guerin, which helped Australia's governing Liberal-National coalition to a surprise election win in 2019 using deliberately provocative tactics aimed at millennials. 

In the UK, the Conservatives have continued using similar tactics on other platforms – setting up a website on Thursday mimicking Labour's to attack Corbyn again. The way they used Twitter to promote that content  illustrates the difficulty of one platform policing the boundary between truth and fakery.

How much is Twitter sacrificing?

Twitter reported total advertising revenue of $702 million for the third quarter of 2019, but political adverts are likely to be an increasingly small proportion of that.

Its most recent Transparency Report lists only 21 organizations paying for political adverts across the EU in the period covering the European elections. 

By comparison, as of 22 November, Facebook's ad library shows that £12.5 million ($16 million) has been spent on 143,143 political adverts on its platform in the UK alone since October 2018. The Labour party spent £432,000 of that and the Conservatives £377,000. 

What are other platforms doing?

Twitter's move was generally viewed as a smart way of exerting pressure on rival Facebook at minimal cost.

Last month, Facebook's Mark Zuckerberg came under fire after he said he had considered banning political adverts because they were more trouble than they were worth, financially, but had decided to err on the side of free expression.

"There are many more ads about issues than there are ads about elections. Do we ban ads about healthcare, immigration or women's empowerment?" he said. 

"If you're not going to ban those, does it really make sense to give everyone else a voice in political debates except for the candidates themselves?"

Google has also decided against banning political adverts, but has introduced greater restrictions than Facebook so advertisers can only target people by age, gender and post code.

Google says it can't adjudicate every claim: "So, we expect that the number of political ads on which we take action will be very limited – but we will continue to do so for clear violations," the company said in a statement.

The restrictions are due to take effect globally by January 2020.