The repurchase agreement market — the repo market — is the circulatory system of modern finance. Trillions of dollars of transactions flow through it daily, yet it is almost entirely invisible to anyone outside the financial industry. When the repo market seizes up, the consequences are immediate and severe: it happened in 2008, and again — more briefly but dramatically — in September 2019. Understanding repo means understanding how banks, governments, and financial institutions fund themselves on a day-to-day basis.
Who uses repo and why
Repo is used across the financial system for different purposes. A bank or broker-dealer with a large government bond inventory uses repo to finance those holdings: it sells the bonds overnight, receives cash, and repurchases them the next morning. Without repo, it would need to fund its entire bond inventory with equity or unsecured borrowing — vastly more expensive. A money market fund or corporate treasurer with excess cash uses reverse repo (the other side of the trade) to earn an overnight return on cash that would otherwise sit idle. Central banks use repo operations to manage overnight interest rates by injecting or draining bank reserves.
The repo rate and monetary policy transmission
The overnight repo rate is closely linked to the central bank's policy rate. When the Bank of England sets Bank Rate, it also sets the rate on its own repo operations — and the private repo market quickly gravitates toward the policy rate as the equilibrium. This is the mechanism through which monetary policy actually travels from the central bank into financial markets: the bank rate flows through repo to SONIA (the Sterling Overnight Index Average), which in turn prices floating rate loans, mortgages, and other instruments. Understanding repo is understanding how central bank decisions are transmitted into the real economy.
Haircuts and systemic risk
In a repo transaction, the lender of cash typically applies a haircut: the borrower posts collateral worth slightly more than the cash borrowed. A 2% haircut on a £100 million repo means the borrower delivers £102 million of bonds but receives only £100 million of cash. Haircuts protect the cash lender from collateral price falls between the repo opening and its maturity. During the 2008 crisis, haircuts on mortgage-backed securities rose dramatically — from near zero to 20–50% — effectively forcing institutions to either find enormous amounts of additional collateral or liquidate assets into a falling market. The repo market's pro-cyclicality is one of its most destabilising features: it provides abundant, cheap funding in calm markets, then withdraws it suddenly and completely at precisely the moment institutions most need it.