The first duty of the leaders and citizens of a democracy is to defend its elections from subversion. Yet a country that boasts of giving the world free parliaments feels no obligation even to look at allegations that Russia subverted British democracy. The government and opposition are compromised and want the scandal closed down. As does an embarrassed rightwing press and a shamefully negligent BBC.

“Suggest we send a note of support to the ambassador,” wrote Andy Wigmore, press officer for Nigel Farage’s Leave.EU just before the Brexit referendum. Documents seen by the Observer suggest that Arron Banks, who gave the campaign the largest political donation in British history, agreed. Whether a note was sent or not, Leave.EU supported the Kremlin line that it was not interfering in British politics. Pause to think about the scene described by Carole Cadwalladr in today’s Observer. The demagogues behind a lavishly funded campaign, whose claim to be patriots was accepted by 52% of the electorate, appeared to be scrambling to provide cover for a hostile foreign power. Why?

I’ll leave you to read our pieces on the contacts between Russia and the Leave campaign and the ties that appear to bind Banks and Farage to Trump and Steve Bannon and on to Russia. Pay particular attention to the offers from the Russians to Banks of a stake in a goldmine. One issue remains: a campaign that purported to be for the “left behind” was organised and funded by men with links across the global network of far-right American demagogues and kleptomaniac dictators such as Putin. We know that Russia has interfered in elections in North America and Europe. Russia had a direct interest in promoting Brexit because it would destabilise a strategic rival. (Anyone who doubts me need only look at how Brexit has brought Whitehall close to collapse.) We know too that the Electoral Commission referred Banks’s campaign to the police for alleged “unlawful overspending” and has raised urgent questions about the behaviour of Boris Johnson and Michael Gove’s supposedly “respectable” alternative, Vote Leave. They deny any impropriety.

Shouldn’t we be following the money?

Broadcasters are a true reflection of a compromised political system

The BBC, meanwhile, has more journalists than any other news organisation in Europe. Given its dominance, it is almost true to say news isn’t news until the BBC says it is. For months, you’d be forgiven for thinking its editors have not let its reporters cover Russia-Brexit. They can report on Trump’s links to Russia – and I suppose we should be grateful for that – but not on allegations of the subversion of the electoral process in the country whose taxes fund them.

If the BBC mentions the Brexit scandal at all, it treats it as boxing match in which the corporation occupies the lofty position of impartial referee. Andrew Marr and the Today programme have both tried to titillate their audiences with catfights between Cadwalladr and Banks and Isabel Oakeshott, who helped Banks with Bad Boys of Brexit. They would be all very well if, to date, the BBC had not failed to produce investigative journalism of its own on the subject. Real journalism is hard work and, if the job is well done, its conclusions, however impartially presented, won’t make comfortable listening for ideological factions and moneyed interests with the wealth to hire libel lawyers.

The usual complaint against the BBC is that, if you assert the world is round, it will scour the country to find a guest to argue that it’s flat. Its behaviour on the Brexit scandal is more disturbing than the usual fetishisation of balance. Rather than report, it has reduced public service broadcasting to a modern version of the Roman circus: a show that stops the plebs worrying their little heads about the future of their country. I’ve defended the BBC against Scottish nationalists, Corybnistas, Remainers and the Brexit right. But how can anyone respect a news organisation that prefers staged confrontations to reporting?

On the Brexit scandal, the BBC offers something worse than fake news: it offers no news. In this, the broadcasters are a true reflection of a compromised political system. Alongside the Electoral Commission, the National Crime Agency and intelligence agencies ought to be investigating. Allegations that foreign states are trying to change the course of a nation’s history are too serious to be left to civil servants and junior officers. You only have to raise the possibility of a British version of the Mueller inquiry to realise why Labour and Conservatives, left and right, would hate it.

The Tories are committed to Brexit. They will not push for investigations into a Brexit campaign whose wishes they are now meeting. Psychologically, Tories and the Tory press cannot separate the Russia allegations from Brexit. They fear that, if they look too hard, the legitimacy of the referendum will dissolve before their eyes.

In the US, opposition Democrats want Trump’s every dealing with Russia exposed. But in Britain the leaders of the opposition Labour party are as anxious as Farage and May to change the subject. Never forget the far left’s soft spot for thieving autocrats. Jeremy Corbyn’s spokesman, Seumas Milne, flew to Sochi to bend his knee to Putin.

Emily Thornberry defended Russia’s Syrian policy as reliably as Arron Banks. Even if you can put its attraction to dictators to one side, the London far left is in a marriage of convenience with the northern Labour right. Both are determined to stop free movement and keep Britain out of the single market: the Labour right because it fears that the charge of being soft on immigration will be electoral poison; the Corbyn left because it dreams of a “lexit” in which it will be free to build socialism in one country. For reasons of ideology and electoral calculation, we are stuck with an opposition that will not oppose.

Can you begin to see why the scandal is not a scandal? In any other democracy, there would be uproar. But here, the Tory and Labour frontbenches must pretend there’s nothing to see. I’ll leave you with the Elizabethan courtier Sir John Harington, who explained in the 1590s how Russia has Britain where it wants it, when he said:

Treason doth never prosper; What’s the Reason?

Why, if it prosper none dare call it treason.

• Nick Cohen is an Observer columnist