DEBT MONETISATION — WHEN CENTRAL BANKS OWN TOO MUCH AND CURRENCIES DIE

What a Currency Actually Is — And Why It Matters

To understand the death spiral, you first need to understand what a modern currency actually is. Strip away the complexity and a currency is a liability on a central bank's balance sheet. The Bank of England issues pounds. Those pounds are liabilities — promises — backed by the assets on the Bank's balance sheet. And what are those assets? Almost entirely government bonds — gilts.

This means the pound is, at its core, a proportional claim on the Bank of England's portfolio of government debt. Each pound in your wallet is backed by a fraction of the gilts the Bank holds. This is not unusual or alarming in itself — it is how all modern fiat currencies work. The question is what happens when the central bank owns so much of the bond market that the currency and the bond market become effectively the same thing.

In a healthy system, the central bank holds a small fraction of total government debt. Most gilts are held by pension funds, insurance companies, foreign investors and banks. These private holders set the price through competition and market supply and demand. The central bank sets short-term rates; the market sets long-term bond prices.

The inflection point occurs when the central bank owns so much debt that it effectively is the market. When that happens, the value of the currency and the value of the bonds become inseparable — and the traditional relationship between interest rates and currency strength breaks down.

Turkey — The Death Spiral in Action

Turkey provides the clearest real-world example of the death spiral in operation. As of recent data, the Turkish Central Bank's balance sheet stands at approximately 12.8 trillion lira — with most of that being lira-denominated government debt. The total outstanding Turkish government debt is approximately 15.5 trillion lira.

When the Turkish central bank owns 82% of the debt, the lira is the bond market. They are the same thing. When the central bank raises interest rates to fight inflation, bond prices fall (because bond prices move inversely to yields). But those bonds back the currency. So falling bond prices mean a falling currency. The very medicine that should cure the patient makes them sicker.

Japan — The World's Third-Largest Economy at the Inflection Point

Japan is the critical case because it is not an emerging market. It is the world's third-largest economy, home to some of the most sophisticated financial institutions on earth, and the issuer of the yen — one of the world's primary reserve currencies. Yet by the metrics of this theory, Japan has crossed or is approaching the critical threshold.

Japanese government debt stands at approximately 1.3 quadrillion yen (¥1,300 trillion). The Bank of Japan (BoJ) at its peak held approximately 644 trillion yen — just under 50% of all outstanding Japanese Government Bonds (JGBs). The BoJ has since begun QT (quantitative tightening), reducing holdings somewhat, but the figure remains extraordinary by any historical standard.

The key evidence cited by analysts tracking this theory is a correlation shift that appeared in the yen around 2022-2024. In a healthy economy, rising yields strengthen the currency — investors buy the currency to access higher returns. But in Japan, a positive correlation has been observed: as JGB yields rise, the yen falls. Rising rates weaken the yen. This is the Turkey effect appearing in a G7 economy.

The BoJ faces a dilemma with no good options. Keep rates near zero and inflation erodes the real value of all those JGB holdings and the yen. Raise rates significantly and bond prices fall, the BoJ's balance sheet loses value, and the yen weakens anyway — while also generating enormous losses on the BoJ's portfolio (it has already realised significant paper losses on bonds bought at near-zero yields).

The Five-Step Global Contagion — How Japan Becomes a US Problem

This is where the theory becomes genuinely alarming. The Japanese and US bond markets are deeply interconnected. Japan is one of the largest foreign holders of US Treasury bonds — approximately $1.1 trillion as of 2026. If Japan is forced to sell those Treasuries to defend the yen, the consequences for US (and therefore global) bond markets would be severe.

Where Does the Bank of England Stand? — The UK's Own Monetisation Journey

The Bank of England's experience with QE and QT is one of the most dramatic in the world — and the numbers reveal both how far the BoE has gone and how different the UK's position now is from the peak.

At its peak in 2022, the Bank of England held £895 billion of gilts — approximately 38% of all outstanding UK government debt. This was below Japan's 50% inflection point threshold, but it was the highest level of central bank ownership in UK history by a very wide margin. The gilt market during this period was effectively a managed market — the BoE was the dominant buyer and its decisions drove prices more than private supply and demand.

Since 2022, the BoE has aggressively pursued quantitative tightening — selling gilts and allowing them to mature. By September 2026, holdings have fallen to approximately £488 billion, down by £407 billion from the peak. As a percentage of outstanding UK government debt (approximately £2.99 trillion), the BoE now holds approximately 16% — well below the theoretical danger threshold, and falling.

This is genuinely good news for the UK's monetary system. Unlike Japan, the UK is actively reducing its central bank ownership ratio. Unlike Turkey, the BoE still owns a minority of the gilt market — private investors, foreign buyers and domestic institutions set prices. The Bank's decisions influence the market but do not dominate it.

How Seriously Should We Take This Theory?

The death spiral theory is compelling and identifies real structural risks. But it should be assessed critically alongside its important limitations.

Where the theory is strong

The core mechanism is mathematically sound. If a central bank owns enough of the bond market, its balance sheet is the currency — and a falling balance sheet means a falling currency. Turkey demonstrates this is not theoretical. The correlation shift visible in the yen (rising yields, falling currency) is documented and real. The interconnection between Japanese JGB selling and US Treasury markets is structural and well-understood by professional investors.

Where the theory oversimplifies

The theory treats all central bank bond ownership as equivalent. But the dollar's reserve currency status provides a buffer that the lira and the yen do not have. Dollar-denominated demand is structural — oil is priced in dollars, global trade uses dollars, and foreign debt is often denominated in dollars. This means the Fed can sustain a higher ownership ratio without triggering the same feedback loop. The 50% inflection point is a theoretical threshold derived from the Turkey/Japan cases — it is not a universal law. The theory also understates the role of institutions, credibility and policy coordination. A credible independent central bank operating transparently can maintain confidence at higher ownership ratios than one perceived to be subordinate to government spending needs.

The bottom line for the UK

The UK is not Turkey. It is not Japan. The BoE's 16% ownership ratio is well below both the theoretical danger threshold and the UK's own 2022 peak. But the theory highlights a genuine risk for the future: if a UK debt crisis forced the BoE back into QE at scale — buying large quantities of gilts to prevent a market dislocation — the ownership ratio would rise again. And the higher it rises, the less effective rate rises become as a monetary policy tool, and the more the currency becomes vulnerable to the feedback loop this theory describes.