Britain wants to spend more. Lenders just repriced it.

Andy Burnham became prime minister on 20 July. John Healey took the Treasury from Rachel Reeves. Within a week the new government had made its direction plain: it wants more flexibility within the fiscal rules. Strip out the phrasing and that means spending more and borrowing the difference.

Lenders answered in days. Investors who hold 30-year British debt pushed the yield they require to almost 5.8 per cent, a level last seen in 1998. At the 10-year point the yield climbed back above 5 per cent. A country borrowing for thirty years does not get to set that number. Its creditors do, and in July they raised it.

Borrowing your way out gets harder the more of it you do. Britain owes £2.99 trillion, equal to 94.9 per cent of everything the economy makes in a year. Servicing that debt cost £11.8 billion in June alone. Announce more borrowing and the yield on new debt rises. When the yield rises, the interest bill rises with it. When the interest bill rises, the room to spend shrinks rather than grows.

That is the loop the gilt market prices every day. Each promise to spend more is met with a higher cost of borrowing, which quietly eats the money the promise was meant to fund. The Office for Budget Responsibility already expects debt interest above £100 billion a year, more than the state spends on most public services. A bigger borrowing plan lifts that figure and narrows what any chancellor can do next.

Governments have an old escape from heavy debt. Let inflation run, and the real value of what they owe shrinks year by year. Britain has bolted part of that door shut on itself. £433 billion of the debt is index-linked, close to a fifth of the gilt stock, and it climbs automatically with inflation. Rising prices lift that part of the bill rather than eroding it.

Recent memory carries the second warning. In autumn 2022 a single budget of unfunded borrowing sent gilt yields up so fast that parts of the pension system nearly failed, and the Bank of England stepped in with an emergency rescue. A calm gilt market can turn into a crisis in days. It has already done so once this decade.

None of this stays in Westminster. Fixed-rate mortgages are priced off gilt yields, not the Bank of England's base rate. A household remortgaging this year pays a rate shaped by what the government is paying to borrow, even while the Bank holds or cuts. A spending plan that lifts yields in July becomes a higher mortgage quote in the autumn.

Business loans, car finance and the rates offered to savers run through the same channel. When the cost of borrowing for the state climbs, the cost of borrowing for everyone climbs behind it.

Set against the borrowing sits a country that looks rich. The national accounts value the UK at £13.1 trillion, roughly four times a year's output. Households hold £10.8 trillion of that. On paper Britain has never been wealthier.

Look at what the wealth actually is. £7.1 trillion of it, more than half the national total, is land. Not houses, not machines, not factories, the price of the ground beneath them. Land builds nothing and exports nothing. Its worth is whatever the next buyer will pay. Take it out and the productive base is thin. British business investment is the second lowest in the G7.

This is the real trouble with borrowing more against this economy. Rising yields swell the debt and, at the same time, pull down the asset prices that make the country look wealthy, because money that can earn 5 per cent in government bonds pays less for everything else. One number squeezes both ends. A state can borrow against a mirage for a while. Its lenders eventually ask what stands behind it.

They have started asking. A 5.8 per cent gilt is the question.