Britain borrowed cheap. It's refinancing expensive.

British government debt does not get refinanced all at once. It is broken into hundreds of individual gilts with set maturity dates. Each one expires; the Treasury borrows again to pay it off; whatever rate lenders are charging that day becomes the new cost.

In the current financial year 2025–26, £168.2 billion of gilts mature. In 2026–27, £140.7 billion will mature. The Debt Management Report's chart shows the schedule running out to 2070–71, with annual redemptions oscillating between roughly £60 billion and £170 billion through the 2030s. The shape of the wall is set. The cost of climbing it is not.

This is one chart and one trend. Every year, a chunk of debt expires. Every year, the Treasury borrows again to replace it. The replacement coupon is whatever the gilt market is asking on the day of issue.

In May 2026, that is between 4.3 per cent at the short end and 5.8 per cent on the long bond. A meaningful share of what is rolling off was issued in a very different rate environment.

To see why the maturity wall matters, you have to look at what is rolling off — not just how much.

The DMO's published gilt list shows that most maturing cohorts from 2026 to 2035 contain a large COVID-era gilt issued at near-zero coupons. The 0.125% Treasury Gilt 2028 (~£40bn outstanding), the 0.5% Treasury Gilt 2029, the 0.25% Treasury Gilt 2031, the 0.875% Treasury Gilt 2033 and the 0.625% Treasury Gilt 2035 are all sitting in the schedule. They were issued between 2020 and 2021, when Bank Rate was 0.1 per cent.

Mixed in with them are older, smaller gilts from the pre-2010 era at coupons of 4 to 6 per cent. The aggregate picture is what matters. Below, the size-weighted average coupon on each maturing cohort is plotted against the approximate refinancing rate at equivalent tenor in May 2026.

Britain holds long. The DMO's Debt Management Report 2026-27 puts the average maturity of the gilt stock at 13.9 years — longer than any other G7 sovereign. The United States runs at about 6 years. Germany, around 8. Conventional UK gilts average 12.9 years; index-linked gilts 16.8 years.

That long maturity used to be a strength. It meant a sudden rise in rates did not flow through to the interest bill immediately. The Treasury had years of cushion built into the schedule.

The same feature is now the problem. Long maturity also means the repricing, once it starts, takes years to finish. It cannot be reversed by a single budget or a single Prime Minister. Even if rates fell sharply tomorrow, the bonds being issued today at 5 per cent would carry that coupon for decades.

The DMR confirms that 8.2 per cent of the debt stock matures inside one year. Compounded across the curve, that is the speed of the wall.

If yields stay close to where they are now, the maturity wall mechanically pushes the debt interest bill higher over the next decade. The arithmetic is simple even if the politics are not.

Roughly £110 to £170 billion rolls over every year through the early 2030s. Across the existing stock, the average gap between today's effective rate of 3.8 per cent and the marginal refinancing rate of around 5 per cent is approximately 1.2 percentage points. Apply that to £140 billion of refinancing per year and each year adds roughly £1.5 to £2 billion to the structural annual interest bill, for the life of the new gilt. Stack the years and the additions compound.

The maturity wall is not the work of one Prime Minister, one party or one decade. It is the cumulative result of fiscal choices made by every government since 1997, every one of which preserved the same basic architecture: borrow now, refinance later, leave the bill for whoever is in office when the gilt matures.

Each of these events was, in its own moment, defensible. Most had cross-party support. None of them reduced the stock of British debt. All of them are now coming due, one cohort of gilts at a time.

The median Gen Z voter was born around 2003. They were five years old at the time of the 2008 bailouts. They were a teenager during the COVID emergency response. They were not eligible to vote in the 2010 or 2015 or 2017 general elections. They will spend most of their working life paying interest on debt issued in their childhood, refinanced at the yields lenders charge today.

Their parents and grandparents are not to blame. The system that produced the debt is older than they are, sits across three decades and seven governments, and was not seriously challenged at any election in that period. Every party in office expanded it. Every party in opposition supported the expansion at the moment of crisis. The bill is what it is.

What younger voters can reasonably ask is that the next thirty years not look like the last. That requires the kind of boring, unglamorous, predictable government that lenders price kindly and Westminster has not produced for at least a decade.