The British political elite has ignored mounting evidence of interference and illegality in the Brexit vote.

Theresa May has had to get used to facing difficult questions about Brexit.

After two years of gruelling negotiations, the British prime minister has spent recent weeks trying to sell the virtues of her proposed Brexit deal to the United Kingdom‘s media, and to often sceptical colleagues in her own party. Whether she has succeeded or failed should become apparent soon.

But there is a major question about Brexit that the Conservative leader still refuses to answer: Was Britain’s 2016 referendum to leave the European Union tainted by illegal campaign funding and foreign interference? And if it was, should there be a full investigation into the Brexit vote itself?

Cambridge Analytica, Russia and Brexit

These are not purely speculative concerns. The last two years have seen mounting evidence of wrongdoing by some of the key players in the Brexit campaign.

Take Arron Banks. The controversial insurance businessman was little known before he spent £8m ($10.4m) on Brexit – the largest political donation in British history. Now he’s being investigated by Britain’s National Crime Agency, after reporting by openDemocracy and others raised serious concerns about the sources of his wealth.

Last week, leaked emails revealed that Banks asked the highly controversial firm Cambridge Analytica for help fundraising in the United States after Steve Bannon, Trump’s former campaign manager, introduced them. (It is illegal under British laws to raise funds from foreign sources; Banks maintains that all his Brexit cash came from his own businesses.)

Banks has faced multiple questions about his links with Russia. Emails leaked to the Observer newspaper showed he had 11 meetings at the Russian embassy in the run-up to the Brexit vote and in the two months after (he initially claimed to have just one “boozy lunch”), and that he was offered lucrative business opportunities by the Russian ambassador. Banks denies any Russian collusion.

Banks also repeatedly misled parliament about how his Brexit operation was run. In May, his Leave.EU campaign was fined for a series of breaches of British electoral law, and the UK’s Information Commissioner’s Office has said that it will levy fines on Banks for breaching data protection laws. There are concerns about whether Leave.EU still holds the personal information of millions of British voters and who else has accessed it.

More dark money

Banks is not the only figure from the successful Leave.EU campaign with question marks hanging over.

Vote Leave, the official pro-Brexit campaign, was found guilty of illegal campaign coordination. The group – headed by former Foreign Secretary Boris Johnson, Environment Secretary Michael Gove and a raft of senior British politicians – broke spending limits by funnelling over £600,000 to a 23-year-old fashion student in the final days of the Brexit campaign.

Meanwhile, Northern Ireland’s Democratic Unionist Party (DUP), the hardline party now propping up Theresa May’s minority government in parliament, also received unprecedented amounts of “dark” money in the weeks before the knife-edge Brexit vote.

The source of a controversial £435,000 donation to the DUP – channelled through a secretive shell company – remains a mystery, thanks to outdated donor secrecy laws that applied only to Northern Ireland. The donation was almost 10 times what the DUP had spent in the entire previous general election – and almost none of the cash was spent in Northern Ireland itself, raising concerns about “donation laundering” and prompting a change in the law.

A country divided

So have British political leaders responded strongly to these grave concerns about where the money for the Brexit vote came from, and whether foreign governments interfered in the vote? Not quite.

If anything unites Theresa May and opposition Labour leader Jeremy Corbyn, it is the desire to move past the 2016 Brexit vote. With their own parties and the country at large deeply divided on Brexit, neither May nor Corbyn seems willing to ask tough questions about the legitimacy of the referendum campaign, or how to protect the integrity of future democratic processes.

On the Brexit vote, it has been left to journalists to do the digging. The indefatigable Carole Cadwalladr at the Observer, our small team at openDemocracy, the Financial Times’ Cynthia O’Murchu and a few other small independent outlets, such as Byline Media, have been responsible for nearly all the evidence that has emerged.

The contrast between the UK and the US is stark. Whereas special counsel Robert Mueller has sweeping powers to investigate Russian interference in Donald Trump‘s presidential election victory – and has racked up a number of indictments and guilty pleas, with more expected to follow – in the UK the only official oversight has come from a UK parliamentary inquiry into “fake news”.

The MPs on this inquiry have not held back in expressing their concerns about the Brexit vote. Their recent report spoke of evidence of “Russian state-sponsored attempts to influence elections in the US and the UK through social media, efforts of private companies to do the same, and law-breaking by certain Leave campaign groups in the UK’s EU referendum in their use of social media”.

But British parliamentary inquiries have limited legal powers. Senior Leave figures such as former Vote Leave campaign director Dominic Cummings have refused to give evidence.

Vote Leave spent more than £3m ($3.8m) on social media advertising with an obscure Canadian data analytics firm that has been linked to Cambridge Analytica. But MPs have no power to compel him to answer their questions.

Facebook supremo Mark Zuckerberg has also refused repeated requests by MPs to give evidence – prompting an unprecedented seizure of court documents this week in order to help British parliamentarians piece together answers to their questions.

Damian Collins, chair of the UK’s fake news inquiry, believes the UK needs an investigation into Brexit similar to Mueller’s probe. Labour’s deputy leader Tom Watson agrees.

The connections between Brexit and the election of Trump are not just rhetorical. Mueller has found strong evidence of ties between London, the Trump campaign and Moscow. Rumours are rife that former Ukip leader Nigel Farage – who still regularly appears on British media – is a key person of interest to the Mueller investigation. It’s also now known that Banks had extensive contact with Trump guru Steve Bannon months before the Brexit vote.

But in Britain, power is extremely centralised. Mueller was appointed by the US deputy attorney general – after then Attorney General Jeff Sessions recused himself from the Russia inquiry. Official inquiries in the UK generally only emerge when there is a cross-party political consensus on the need for an investigation. The Leveson inquiry, for example, was a response to widespread outrage about phone-hacking. Even then, such inquiries in the UK do not have Mueller’s powers to assign blame or issue prosecutions.

A ‘pinch of Kafka’

Britain, famously, does not have a written constitution. Convention generally triumphs. And this way of doing politics is looking increasingly shaky.

During the summer, senior figures from both Vote Leave and Banks’s Brexit campaign were reported to the Metropolitan police for breaching the British electoral law. But as of last month, the police had not yet even opened these investigations – citing “political sensitivities” around the Brexit vote. A phrase Orwell would be proud of.

Theresa May has also refused to deny newspaper reports that she prevented British intelligence services from investigating Banks when she was the home secretary in 2016. Last week, it was revealed that the British Home Office was refusing to release information about the case, as to do so might “impede the future formulation of government policy”. May’s critics rounded on her, calling it a “lame excuse” for a “cover up” with a “pinch of Kafka”.

Meanwhile, a former Democratic Unionist Party (DUP) politician has just been appointed to a key role at the Electoral Commission, Britain’s elections watchdog – the body that should be investigating the sources of the DUP’s controversial Brexit cash.

Conservative MP Damian Collins, chair of the fake news inquiry, has warned of “a crisis in our democracy – based on the systematic manipulation of data to support the relentless targeting of citizens, without their consent, by campaigns of disinformation and messages of hate”.

But so far British political leaders have failed to heed the warnings. The time has surely come for a Mueller-style investigation to get to the bottom of exactly what happened during the UK’s most important vote in decades – and to prevent such exploitation of the electoral process happening again.

The views expressed in this article are the author’s own and do not necessarily reflect Al Jazeera’s editorial stance.