Should the EU referendum result be annulled? For the past year I’ve been arguing that this would mean defying a democratic decision – even if it was informed by lies. Democracy is not negotiable. But what if this was not a democratic decision? What if it failed to meet the accepted criteria for a free and fair choice? If that were the case, should the result still stand? Surely it should not.

The great British Brexit robbery: how our democracy was hijacked Read more

As the months have rolled by, these questions have become ever more troubling. Since the Conservatives struck their deal with the Democratic Unionist party (DUP) this week, they have come into sharper focus.

There are several reasons to be concerned about the way money was spent and public opinion was influenced in the referendum campaign, some of which have been exposed by Carole Cadwalladr in the Observer. Among these issues is the funding passed through the DUP in Northern Ireland.

What we know so far, as a result of investigations by the website openDemocracy, is that the DUP channelled £425,000 into the leave campaign. Most of this was used not in Northern Ireland but in England and Scotland. Could the reason that this money was passed through Northern Ireland be that, uniquely in the United Kingdom, political funders there are allowed to remain anonymous?

This anonymity might have made sense during the Troubles, when donors to political parties could have been targeted by paramilitaries, but it’s now an anachronism. The Northern Ireland Act 2014 allows the Westminster government to create secondary legislation, removing this privilege. But it has failed to use this power.

Now that the government depends on the DUP, this is unlikely to change. It means that Northern Ireland remains a potential pipeline for opaque political funding that can be spent anywhere in Britain.

I can think of three possible reasons for someone to wish to keep their spending anonymous. The first and most innocent is that a donor might simply wish to keep their name out of public life. Even this is problematic. If someone is spending major money on politics, the democratic principles of accountability and transparency surely demand that we should know who they are.

The second possible reason is that the money comes from an impermissible source, such as a person not listed on the UK electoral register. The third is that the money comes from a campaign that has already reached its spending limit, and has farmed out the surplus to another group that can then act as its proxy. At the moment, there is no means of telling whether any of these possible explanations are correct.

All we have is an admission by the DUP that the money came to it through an organisation called the Constitutional Research Council. We know nothing about this group other than that it is based in Scotland and run by a man called Richard Cook. He was formerly vice-chairman of the Scottish Conservative party. In 2013 he founded a company with the former director of the Saudi Arabian intelligence agency. My efforts to speak to him have so far been unsuccessful.

The coordinator of the DUP’s leave campaign, Jeffrey Donaldson MP, told openDemocracy that “we don’t need to know who made the donations” to the Constitutional Research Council. But election law says: “If you are given a donation on behalf of someone else, the person giving you the donation (the agent) must tell you … the actual donor’s details.”

During the battle over the European referendum campaign, the designated lead campaign groups on either side were allowed to spend up to £7m. Vote Leave spent £6,789,892, but it received over £9m. So what happened to the rest of the money? We know that it gave some of it to other groups with similar aims, including £625,000 to a tiny organisation called BeLeave, run by a 23-year-old fashion student, and £100,000 to a group called Veterans for Britain.

The legality of these sub-donations hangs on the extent to which the campaigns were “coordinated”. If, the rules say, the different campaigns used joint advertising efforts or materials, or carved up the tasks between them, or if one group exercised influence over others, this funding – if it collectively exceeds the spending limit for the designated lead campaign – is illegal.

A lack of curiosity about this case appears to be infectious

This is why the questions raised by Cadwalladr over why and how the different leave campaigns – including Vote Leave and the DUP – used the same obscure data company in British Columbia are crucial.

Now openDemocracy has raised further concerns, after reporting that Vote Leave, Leave.EU, Grassroots Out, Ukip and the Democratic Unionist party all used a tiny branding agency called Soopa Doopa, based in a house in Ely, Cambridgeshire. Vote Leave spent £637,000 with this agency; the DUP spent nearly £100,000. There is no suggestion that Soopa Doopa did anything wrong, and others have denied coordination.

I asked Matthew Elliott, who ran Vote Leave, whether the £425,000 the DUP received might have come from his organisation. He told me “I can confirm that Vote Leave wasn’t the source of the funding.” When I pressed the DUP on the matter, it told me that the money “came from a permissible donor, who in turn are themselves regulated by the Electoral Commission”. Intriguing, but not enlightening.

What has the Electoral Commission done to investigate this funding? Nothing. It first received a complaint about the issue a year ago. It failed to act on it, but claims to have “fulfilled its statutory duties”. A lack of curiosity about this case appears to be infectious.

Perhaps it has failed to investigate because it knows there is nothing meaningful it can do. It notes that the only means of challenging the outcome of an election are “outdated, complex, inaccessible and inefficient” – essentially unchanged since 1868. Only candidates and voters can question a result, the commission is forbidden to do so. All it can do is issue pathetic fines.

A decision of such significance, whose implications are likely to be felt in this country for generations, should be above any possible suspicion of manipulation. Knowing what we know now, I do not believe this can be said about the EU referendum. So do we leave this monumental issue to a body which – by its own admission – is constitutionally incapable of challenging a result, even if that result has been obtained unfairly?

No. Though I am a lukewarm European – a Eurosceptic remainer – it now seems clear that the credibility of our political system demands that Brexit should be halted until the means by which the result was obtained have been thoroughly investigated, ideally by a public inquiry. If the outcome of such an investigation is that serious breaches of electoral law have taken place, the referendum should be annulled and repeated. Is this not what democracy entails?

As soon as a new petitions committee is established, I will post a petition to this effect on the UK parliamentary website. I would urge you to sign it.