The revelations over the weekend from the brave and principled former BeLeave treasurer Shahmir Sanni are devastating. His claim that £625,000 was donated by Vote Leave to his supposedly independent pro-Brexit referendum campaign organisation – and channelled to a digital services firm with links to the controversial Cambridge Analytica – if proven, means a flagrant violation of election rules, as it was not a genuine donation.

Sanni stated, too, that BeLeave shared offices with Vote Leave – fronted by Tory MPs Boris Johnson and Michael Gove – which allegedly in practice offered advice and assistance to the group and helped it to decide where its cash would be spent. British electoral law forbids different campaign organisations acting in concert unless they have a shared cap on spending.

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In what one can only assume was a state of panic, Theresa May’s press office swiftly put out a statement that, among other things, outed Sanni as a homosexual – a tactic that places his family at considerable personal risk due to his Pakistani heritage.

Tellingly, Gove did not respond directly to the allegations and the foreign secretary declined invitations to go on air to talk more fully on the subject, or take any supplementary questions – presumably on legal advice. Sanni has passed on his evidence to the Electoral Commission and the police.

Much depends now on the independence and courage of the commission and its chief executive, Claire Bassett. But, in the meantime, let us be clear about the point we have now reached: if the decision we took on 23 June 2016 to leave the European Union had been a verdict arrived at in a court of law, it would now be deemed questionable and a retrial would have to be ordered.

As transparency campaigner for more than 10 years, I have long had a sense that something was not quite right about the EU referendum. I warned back in November 2017 that the leave campaign seemed to be awash with dark money that may have circumvented rules designed to uphold the integrity of our democratic process. There have already been claims that the mysterious Constitutional Research Council routed £425,000 into pro-Brexit advertisements in London via the Democratic Unionist party. In 2016 the same organisation gave the Tory MP Steve Baker £6,500. At the time Baker was chairman of a Tory hard-Brexit caucus, the European Research Group, which was behind the letter that Johnson and Gove recently sent to the prime minister ordering her not to dare to stray from the Brexit path.

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The Electoral Commission is already investigating the funding of Leave.EU and its largest donor, Arron Banks, who has always protested his innocence over the allegations made against him. These allegations focus on whether donations were permissible, and on whether Banks or his company acted as an agent for other donors. Vote Leave is also now under investigation for potentially breaching the rules over the £625,000 BeLeave donation, given to 23-year-old fashion student Darren Grimes.

Much has emerged too of Russia’s tampering with our democratic process which, while now the subject of an exhaustive investigation in the US, has still to be properly examined here – though, thankfully, tenacious individuals such as journalist Carole Cadwalladr and MP Ben Bradshaw, have persistently raised questions.

The essential problem we have on this side of the Atlantic is that, in our very British way, we are conducting our politics like a family that steers clear of certain subjects because they are embarrassing. Theresa May has been uncomfortable about tackling the subject of Russia because she knows very well that its oligarchs were getting a foothold in the UK during her time as home secretary. What is more, this all gets into the awkward issue of the roubles that have for years been donated to the Tory party.

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This is far too important a subject for us to take the view – for reasons of political expediency and pride – of “least said, soonest mended”. It’s not good enough either to say, as the BBC’s Andrew Marr did on his show recently, that it is all “very complicated”, implying that we shouldn’t even bother to try to get our heads around it.

I fought for MPs to have the right to vote on article 50 not because I was against Brexit, but because I was, and remain passionately, an advocate of parliamentary sovereignty. These latest revelations from Sanni should concern every one of us, because they are ultimately about whether ours is still an honest and fully functioning democracy. That is fundamentally more important than Brexit.

Yes, I believe in parliamentary sovereignty, but irrespective of what the Electoral Commission decides, I am now even more convinced that there must be a people’s vote on the Brexit deal, including an option to remain, or remain voters will have good reason to shout foul play.

It is time for us, the people, to deliver our verdict not on whether we should leave Europe, but on the far more important question of what has happened to our democracy.

• Gina Miller is a businesswoman and transparency activist. She was the lead claimant in the successful legal fight to allow parliament to vote on whether the UK could start the process of leaving the EU