If you have been on social media over the last few weeks, you may have seen people tagging posts with the hashtag #FBPE, or using #FBPE in their usernames. But what does it mean?

The hashtag was first used on Twitter in October by Hendrik Klaassens, a Dutch social media user, who posted: “#ProEU tweeps organize Follow Back Saturdays! Type #FollowBackProEU or #FBPE if you want to get more #ProEU followers. Let’s do this!” in an attempt to build up a network of pro-EU users.

Why have British people been using #FBPE?

With Brexit on the horizon, the idea soon took on a specific twist in the UK, becoming a way for remain voters and pro-EU social media members to identify each other online. Many Brexit supporters have made themselves easy to spot by incorporating flags into their usernames and online biographies, and the aim was to make a similarly easily recognisable signal. The Liberal Democrat activist Mark Pack described it as “a pro-EU version of the #ff ‘follow back Friday’ trend on Twitter – an easy way to highlight who else may be of interest to you”.

Having spotted it, Mike Galsworthy, the co-founder of Scientists for EU, decided it could be useful for encouraging grassroots campaigning, and made several videos promoting it.

Why do some remain voters find it divisive?

Just as there are many different types of leave voter, with different ideas of what Brexit should look like, there are also many different types of remain voter. Klaassens clarified the hashtag’s purpose in December, tweeting:

There have been accusations among some UK users that the hashtag has been used to criticise and undermine Jeremy Corbyn’s position on Brexit and his leadership of the Labour party. In part this reflects a divide along party political lines, with Lib Dem and Scottish National party users of the hashtag being critical of the position Labour has taken. Some Corbynites have instead conglomerated around a different hashtag – #PCPEU – standing for pro-Corbyn, pro-EU.

Galsworthy welcomes this, stressing the need to build a “broad umbrella” of pro-EU activists. “There’s a significant number of pro-EU people among the Corbyn supporter base – the #PCPEU hashtag took off pretty damn quickly.”

The idea of an automatic followback on the basis of your Brexit stance does not appeal to all remain voters. A Twitter user, Michael Goodier, said: “I like to try to keep my Twitter timeline diverse in terms of opinion, and following a load of pro-EU accounts simply for the fact they’re pro-EU would ruin that. I also don’t want people to follow me for my Brexit stance, but based on my tweets. I get that it’s an identity thing, but the fact you’re telling people to follow you seems to me to be a bit of a beg.”

And has it been hijacked?

Well, yes. “At first Brexiteers didn’t know quite how to respond,” explains Galsworthy. “There were various attempts to try to set up alternatives, and then to use the #FBPE hashtag and try to infiltrate and redefine it.”

You can now find leave voters on social media with #FBPE in their username or bio – but for them it stands for “Full Brexit Prompt Exit”. That rewording of the acronym started on Twitter at the end of December, and one of the earliest examples was in a reply to Guy Verhofstadt tweeting about European unity.

The talkRadio host Julia Hartley-Brewer was one prominent leave supporter who added the hashtag to her username for a while in early January. At one point it was estimated that about 3,000 accounts that looked like leave supporters had incorporated the hashtag into their social media use.

And some of the apparent leave voters pushing this remade acronym seem happy to give the impression of coming from further afield than the UK’s Brexit voting areas – regardless of where they may actually be posting from.

Those behind the hashtag have encouraged genuine users not to attack leave voters getting involved. “Whenever you see that happening,” said Galsworthy, “we encourage people to welcome them, and thank them for flagging up #FBPE politely.”

Is it having any impact?

Those behind the hashtag believe it is, and they cite the fact that in December Lord Ashcroft blamed the hashtag for swinging an unscientific Twitter poll he was conducting about possible outcomes for a second referendum.

“The network effect has been really useful – spreading news between remain supporters very, very quickly. And whenever anything is successful, people want to jump in on it,” Galsworthy says of the attempts to hijack it, “and the same thing has happened here.”