A year ago today, the Electoral Commission found that Vote Leave broke the law. Next week, the man who fronted that campaign is almost certain to become prime minister.

The finding came on the back of months of investigative journalism. Alongside Carole Cadwalladr at The Observer and reporters at Buzzfeed, we gathered documents and spoke to sources and collated evidence.

Eventually, our collective coverage forced the Electoral Commission to reopen an investigation they had previously closed. Eventually, the watchdog of our democracy said that the campaign, fronted by Boris Johnson and Michael Gove, had exceeded its £7m spending limit by £449,079.34.

For exceeding its spending limit by hundreds of thousands of pounds, Vote Leave was fined £20,000. The group was fined another £20,000 for failing to comply with the commission’s investigation, a further £20,000 for filing false information, and £1,000 for failing to produce invoices to evidence what it said it had spent: a total of £61,000 of fines for £7.5 million of spending, or less than 1% of the total.

The commission wanted to fine Vote Leave more. But the law limits them – the maximum they are allowed to fine for a broken rule is £20,000.

At the same time, the Electoral Commission announced that it was referring Vote Leave to the police for its overspend. Breaking electoral law is, after all, a crime. So I scrolled ahead a few months in my phone calendar and set a reminder to chase up the Metropolitan Police, and ask what they had done about this.

In September, we published the consequence of that reminder. The Met still hadn’t opened an investigation into Vote Leave. When my colleague James Cusick asked them why not, the police cited “political sensitivities”.

When the story exploded online, Green London Assembly Member Sian Berry asked mayor Sadiq Khan why nothing seemed to have happened. He replied that he’d been told by the Met that they had only recently received the relevant documents from the Electoral Commission. But when I asked the commission about this, they told me a different story: the Met had been told months earlier that the documents were in their basement, ready to collect. They just hadn’t bothered to pick them up.

The point of telling you this story is simple. We can’t trust the police to guard the laws of our democracy, and stop it being bought by the mega-rich. And the Electoral Commission doesn’t have the teeth it needs to enforce the rules.

There’s a huge amount we need to do to deepen our democracy. Much of it will take slow, careful deliberation. But right now we’re facing an emergency: if Boris Johnson makes it to Downing Street, it will be a clear sign that those who take money from millionaires can break the laws of our elections and still rise to the top of our politics.

And so we need to move quickly – to show the mega-rich that we won’t allow our democracy to be drowned in dark money.

And that means that the Electoral Commission has to be given the power to bite back. £20,000 is a paltry amount to the mega-wealthy. After all, Boris Johnson once described his £250,000-a-year second salary as “chicken feed”.

That’s why we’re calling on David Lidington, the Cabinet Office minister, to rush through a law giving the commission the power to levy whatever fine is proportionate to the crime. Because we need to send a clear message: our electoral law exists to stop the super-rich from buying our elections. We won’t stand by as it is ignored, or treated as a minor inconvenience by those it is meant to hold to account.

There could well be another election or referendum later this year. And so we’ve launched a petition with the campaign group 38 Degrees, demanding that MPs give the Electoral Commission the teeth it needs to act as a real guard dog for our democracy. Please sign it.