Do you know the result keeping them awake at Number 10? It's not Scotland. It's not Wales. It's London, the shiny new heartland Labour built for itself and now can't stop worrying about.

One in seven Labour MPs represents a London constituency, including the Prime Minister, his deputy David Lammy, Health Secretary Wes Streeting, and Housing Secretary Steve Reed. A significant chunk of the party's activists and leadership voters live in the capital. Losses here would hurt Labour's core - like a paper cut from a very important document.

But virtually everyone expects serious losses. YouGov predicts it could be Labour's worst result in London in almost 50 years. The squeeze is coming from both sides: the Greens in progressive inner boroughs like Hackney, and Reform UK in the more socially conservative outer ring. The Conservatives and Liberal Democrats also hope to gain some councils.

Tony Travers, a politics professor at the London School of Economics, says the capital may be about to witness a "political earthquake." That's not the kind of tremor Labour leaders were hoping for.

It's all a far cry from 6 May 2010, when Labour lost its parliamentary majority but increased its majority in both Hackney constituencies. Over the next 14 years, Labour strengthened its control of councils, Sir Sadiq Khan won three mayoral elections, and at the 2024 general election, the party won 59 of London's 75 parliamentary seats.

This year, all 32 councils and five borough mayors are up for grabs. In the last local elections (2022), Labour won 21 councils. Now, polling by YouGov and JL Partners suggests they could lose top position in several. Everyone agrees it will be a rough night for the governing party in London.

In Hackney, the Greens are hoping to take a council Labour has run since the 1970s. YouGov predicts Hackney will fall to the Greens. Leader Zack Polanski campaigned at Ridley Road market, where one woman told us she's "really fed up with getting poorer and poorer as I get older." An Ipsos poll found 54% of Britons rank cost of living as a "very important" issue. Prof Travers notes the Greens now talk less about the environment and more about anti-austerity, workers' rights, and anti-fascism. Their manifesto puts "Climate and Environmental Justice" at the bottom of their priorities.

The Greens call for a wealth tax, tougher rent controls, and 100% council tax relief for lowest-income residents. They claim to block the rise of Reform UK and defend migrants' rights. Polanski has had to defend promises like legalising class A drugs, decriminalising sex work, cutting police funding, and ending "discriminatory policing of delivery riders." His coalition - young, anti-wealth, urban, Muslim, anti-Israel - resembles Jeremy Corbyn's.

One woman at the market summed it up: "With my head it's Labour. With my heart it's the Greens."

Further out, in Barking and Dagenham, the challenge is from Reform. YouGov predicts Labour will lose the council to Nigel Farage's party. The share of the white population dropped from 58% (2011 census) to 45% (2021), and the borough has a relatively high number of asylum seekers. Union Jacks and St George's crosses fly on lamp posts. Ella, at the BabyZone hub on the Beacon Tree estate, says some residents don't love the demographic change: "People haven't integrated well together." Dave, at a local pub, complained, "The refugees don't want to work. Everything's a hand-out." Farage has promised a referendum on leaving London to rejoin Essex.

The Conservatives hope to retake old strongholds Westminster, Wandsworth, and Barnet - all lost to Labour in 2022. YouGov puts the Tories ahead in Barnet (25%, six points ahead of Labour). They hope a few wins might distract from an otherwise difficult night, just as they did for Margaret Thatcher in 1990 - though she was driven out of Number 10 six months later.

The Liberal Democrats, polling about the same as four years ago, hope to hold Kingston, Sutton, and Richmond, and potentially win Merton. But they're not predicted to make a stronger advance, a sign of the fragmented nature of modern British politics. No party may win overall control of many councils, leading to difficult compromises to run local services.

More than six million people can vote in London - about the same as Scotland and Wales combined. The results will determine who runs vital services like schools, social services, and rubbish collection. They could also signal Labour's fate nationally. As Mayor Sir Sadiq Khan put it: "We're in danger of being stonked."