The UK's 10-year bond yield just hit 5%. That's the highest level since 2008.
Bond investors aren't pricing a debt crisis. They're pricing a political one.
Prime Minister Keir Starmer's hold on the top job is slipping fast.
As of Monday, 77 of his own Labour MPs had called on him to resign. The loudest voice was Home Secretary Shabana Mahmood.
By Tuesday afternoon, three junior ministers had quit. The first to go was Miatta Fahnbulleh, a junior minister in the housing team.
A Monday speech meant to calm the rebellion fell flat. Several aides quit later that night.
The trigger was a brutal showing in last week's local elections. Labour lost more than 30 councils and around 1,500 councillors.
Voters fled to the right-wing Reform UK party and the left-wing Greens at the same time. It's rare for a ruling party to lose votes to both ends of the map in one night.
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A new Labour leader could mean a fresh fiscal path. That's what's spooking bond investors.
The UK's 10-year bond yield is the rate the UK pays to borrow for 10 years. It climbed to 5% Monday, with the 30-year hitting 5.67%.
Both are the highest readings since 2008.
Deutsche Bank said markets are bracing for the chance that a new leader might "ease the fiscal rules and raise gilt issuance." In plain English, borrow more, faster.
The selloff in UK bonds matters for U.S. investors too. When borrowing costs jump in a big economy, it tends to drag global yields higher.
Eurasia Group put the odds of Starmer being ousted this year at 80%, up from 65% a few days ago.
The most likely path is MPs forcing a leadership vote by September. After that, the next most likely paths are an orderly handover or an immediate vote.
Possible names to replace him include Manchester Mayor Andy Burnham, former deputy Angela Rayner, and Health Secretary Wes Streeting.
None have made a public move yet. The Telegraph said six of 22 Cabinet ministers were set to tell Starmer to quit.
Discontent inside Labour has been building for months.
Voters were unhappy with the failure to slow illegal entry by boat across the English Channel. The government also took heat for trying to cut welfare spending.
A string of policy U-turns left the party looking weak. That cost the government real credibility with investors well before this week's market moves.
The Labour government also faced pressure on the chancellor's fiscal rules. Markets had already priced in some risk that those rules would be loosened.
This week's selloff is what happens when "some risk" turns into "high risk" in days.
Starmer's office put out a statement Tuesday saying the prime minister does not intend to quit. It also said the formal Labour process for challenging a leader has not been triggered.
Markets are pricing in a different outcome. Bond yields don't usually jump like this on noise.
No sitting Labour PM has ever been forced out by their own party. If Starmer goes, it sets a precedent every UK investor will be watching.
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