Anti-Brexit groups are running at least twice as many adverts as major Leave campaigns on Facebook – and possibly up to 59 times more, Sky News can reveal.
The two largest Remain campaigns, People's Vote and Best for Britain, are currently running 16 Facebook ads on their pages.
By contrast, Leave Means Leave, the group backed by Nigel Farage, is running five ads. Leave.EU is only running two.
A data set of Facebook ads over the last two-and-a-half months, seen exclusively by Sky News, presents an even starker contrast.
In this period, the Best For Britain and People's Vote campaigns ran 177 ads, whereas the two largest pro-Brexit campaigns ran only three.
Ahead of the Remain-supporting March for the Future taking place in London on Saturday, People's Vote and Best for Britain aimed ads at different geographic regions of the UK – including Swansea, Edinburgh, Hackney, Liverpool and Stoke.
It also targeted ads at supporters of Premiership football clubs, including West Ham United and Manchester City, telling fans how much their club had lost out on in the transfer window as a result of the weak pound.
Tom Baldwin, director of communications for People's Vote, told Sky News that the campaign had also targeted Facebook users in the West Midlands after the boss of Jaguar Land Rover said that Brexit could put tens of thousands of jobs at risk.
Baldwin said the People's Vote campaign had increased the number of ads it was putting out in recent weeks, adding: "We've just really started doing this, and we've managed to reach around two or three million people, that's the kind of impressions that we're getting."
The historic Facebook ads come from a start-up called Who Targets Me, which uses a free browser plug-in to collect Facebook ads from around 10,000 different news feeds. It pulls in between 7,000 and 8,000 ads a day, many of which are related to Brexit.
"There's a lot more advertising coming from the Remain side," said Sam Jeffers, one of the project's founders. "We're not seeing a lot of stuff on the Leave side at the moment.
"Maybe that's confidence on their side, that things are going the way they want it to be, or maybe those campaigns haven't really got going yet."
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During the 2016 referendum, the official Vote Leave campaign spent more than £2.7m on Facebook ads, using data taken from social media and other sources to target specific groups with tailored – often wildly exaggerated – messages.
Baldwin denied he was repeating the same practice: "We're trying to reach people in a straightforward way using existing Facebook tools."