In 1991, I began trading for Morgan Stanley, the investment bank, in London. I was trading bonds, derivatives and related securities. One of those securities was based on the three-month Libor rate: the interest rate at which banks can borrow money for three months from each other. Morgan Stanley does not trade on the interbank market so I could not directly borrow or loan money at Libor rates. What I could do, however, was trade a futures contract on the three-month Libor rate.

As an example of how a futures contract works, consider the following. Suppose that we are concerned about three-month Libor rates increasing in the future; in particular, we are concerned about what the three-month rate will be in September. If that rate is, say, 1 per cent, we can agree today to effectively lock it in. If, come September, the actual three-month rate is 2 per cent, then our contract will ensure we can still borrow at 1 per cent. Futures contracts on three-month Libor were – and are – traded on the London International Financial Futures Exchange (Liffe, now part of NYSE Euronext). There was a standard contract for the month of September. That contract had its rate settled on the third Wednesday of the month, at 11am.

In 1991, I had live trading screens that showed the Libor rates. In September of that year, on the third Wednesday, at 11am, I watched those screens to see where the futures contract shouldsettle. Shortly afterwards, Liffe announced the contract settlement rate. Its rate was different from what had been shown on my screens, by a few hundredths of a per cent.