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Over the past three months, , a pro-Brexit group, has spent more on political advertising on Facebook than anyone - more even than .

So last week I called a prominent figure in the Brexit camp about it. Did he know , the only person publicly associated with the group? "Yes". Did he know who was funding him? "No, but…"

And there followed a proud sermon on how political donors are using groups like Britain's Future to influence public debate.

It goes like this. There are a huge number of donors, who support Brexit. They were very much for Leave in June 2016; in many cases, they have been against Britian's membership of the European Union for decades. They are rich. But they don't want to stick their head above the political parapet.

To do so risks the ire of Remainers, constant interrogation by journalists, scrutiny from regulators, and perhaps social isolation in some circles.

So, this Brexiter said, they pump money into groups like Britain's Future instead. This allows them to go largely undetected. They get the upside of influence and a feeling of contributing to the cause, without all the hassle.

In our report for last night's 10 O'Clock News, produced by Elizabeth Needham-Bennett and picture edited by Kavi Pujara, we looked at how the public can now see some of the analytics and origins of advertisers on Facebook. But not, of course, who is paying for the ads.

There's a short version of our report at the top of this blog.

on Britain's Future on Saturday. over the weekend too. And my distinguished colleague when he approached him in November - including the insistence that he wouldn't be releasing the names of his donors.

To the best of our knowledge, Britain's Future has done nothing illegal. That's the point. The trouble is, given they have spent well over £300,000 in the past few months, and given that last week's expenditure of over £50,000 may not be affordable by Dawson alone (aside from political activism, he is a freelance journalist and comedy script-writer), it is easy to see why all citizens have an interest in knowing who is paying for all these ads.

Moreover, given the explicit argument made by that prominent Brexiter - that donors use these groups as a way of circumventing public scrutiny - we have an issue that is growing bigger and more dangerous. What if someone - whether Leaver or Remainer - pumps millions into Facebook ads in the week before 29 March?

The Cambridge Analytica scandal alerted millions of voters, and some regulators, to the danger of these so-called dark ads.

It is undoubtedly true, as Sam Jeffers of Who Targets Me argues, that Facebook has come a long way on transparency. In response to both that scandal, and the suggestion that Russia may have used that platform to interfere in the US presidential election, the company has made it much easier for any user to have a rummage around its ad library.

Facebook says that, once it has checked advertisers are based in the UK, it's up to regulators to investigate whether any law-breaking is going on. Alas regulators haven't yet got the power to get their hands dirty in this area. Political advertising on Facebook seems to fall between the Electoral Commission, the Information Commissioner's Office, and the Advertising Standards Authority.

In its recent report on Fake News and Disinformation, the DCMS Select Committee made the inadequacy of electoral law one of its headline findings.

There is a pattern here familiar from all the debates about the intersection of digital technology and the law - whether pertaining to images of self-harm, fake news, Russian interference or indeed Britain's Future.

Technology is fast and unpredictable; regulation is slow and consensual. It is hard to devise new laws and regulations to keep up with innovations that no law-maker could or would foresee. This incongruity, between technology and democratic scrutiny, creates a gap that can be exploited in a legal and impactful way.

So it is that dark ads are a constant influence in our democracy. For donors, they are precious. For lawmakers, they are an urgent threat. And for voters, they are an untimely exposure, given democracy is currently enduring something akin to .

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