Pro-EU groups have rushed to buy adverts on Twitter before a global ban on political advertising kicks in on Friday.
Twitter chief executive Jack Dorsey announced the ban in October, saying that the reach of political messages "should be earned, not bought".
The move seemed to have had a chilling effect on political parties, with only the Conservatives placing a Twitter ad.
However, several pro-Remain campaign groups have run ads on the platform.
The BBC found four separate political groups campaigning against Brexit had purchased ads, taking advantage of Twitter's targeting tools before they were taken away from political causes.
A total of 31 adverts have been run by the groups as promoted tweets with messages such as "Brexit: A threat to women's rights" and "We need your help to stop Johnson".
Promoted tweets are posts that appear in a person's feed regardless of whether they follow the advertiser's account. The adverts can be targeted at people based on their age, location, gender and interests, including political leanings.
No pro-Brexit advertising could be found on the platform in the week leading up to Twitter's ban.
However, in the final few hours before the ban, the Conservatives placed an ad attacking Jeremy Corbyn.
The most prolific advertiser was Best For Britain, which describes itself as a campaign to "stop Brexit by any democratic means". It told the BBC it had spent £31,000 on Twitter ads since the election was called.
The pro-Remain group is funded by donors and is the third-largest spender on political advertising on Facebook and Instagram.
On Twitter, the campaigners have run 11 ads in the last seven days with messages such as: "Follow us if you think Brexit should be stopped".
They have also been calling on voters to choose certain candidates based on tactical voting research.
Best For Britain chief executive Naomi Smith said the group had been rushing to buy ads before it became prohibited.
"We've been trying to grow our followership before the ban comes in so that we have a larger audience and can spread our message more organically after the ban," she said.
"We've seen some good results and have promoted threads to audiences that we know we need to reach by targeting young women who, for example, have concerns about jobs or live in marginal seats."
Like Facebook, Instagram and Snapchat, Twitter allowed advertisers to target people using specific criteria such as their political leanings and other sensitive information that is gathered based on a person's activity on the platform.
On Thursday, Google announced a worldwide ban on this granular form of targeting in political adverts.
Twitter does not give details of how much each advert cost or how many people saw it.
BBC research found the recent pro-Remain ads had gathered 15,500 likes and more than 6,500 retweets.
The other groups advertising on Twitter were For Our Future's Sake, People's Vote UK and Scientists for EU.
Alex Tait, co-founder of the Coalition for Reform in Political Advertising, said Twitter's ban was a significant move but more symbolic than practical.
"Twitter is not a big place for political ads when you compare it to Facebook and Google," he said.
"Only around £50,000 was spent on the platform in the last election."
He said banning political ads had been Twitter's choice.
"Other platforms have different ideas, so this shows once again that there needs to be regulation around all political advertising to bring about consistent rules."
These may be the last political ads on Twitter, but that does not mean political campaigning will end on the platform.
In the future, however, politicians and groups will have to rely on finding an audience organically rather than reaching them via paid-for promotions.