Sterling lost as much as 10 percent of its value in just a few minutes of trading early yesterday, a "flash crash" that fuelled concerns about the vulnerability of the currency and other British assets to investor worries about Brexit.
The pound recovered from the initial plunge, which took it as low as $1.1491 in Asian hours and was driven, dealers said, by the automated algorithmic computer trades that now dominate the global foreign exchange market.
But selling by European and U.S. investors quashed any bounce as first London then New York came on line, driving a 2 percent loss on the day and putting sterling on course for its biggest weekly fall since 2009.
The fall in sterling sounded like good news to investors in internationally focused UK firms, which gain on overseas revenues and competitiveness when the currency falls. The FTSE 100 index was up 0.6 percent at its close, led by mining companies and Asia-exposed banks Standard Chartered and HSBC while other European stock markets fell sharply.
There are growing worries about the impact sterling's losses and the Brexit nerves behind them will have on domestic demand, inflation and economic growth in the years ahead
But there are growing worries about the impact sterling's losses and the Brexit nerves behind them will have on domestic demand, inflation and economic growth in the years ahead.
Ten-year gilt yields rose by as much as 11 basis points to 0.984 percent, the highest since the week of the referendum vote to leave the European Union in June. <GB10YT=RR>
The FTSE 250 index of medium-sized UK firms, typically more dependent on the domestic market, marked its third straight session of losses after hitting an all-time high on Tuesday. <.FTMC>
“This is the first sign in a couple of months that there is some market concern about a Brexit," said Jonathan Roy, advisory investment manager at Charles Hanover Investments.
"What we're seeing playing out is domestic-facing stocks weakening in the face of a potentially 'hard' Brexit ... while we're seeing strength in the FTSE 100."
Hedging costs
Sterling has been falling steadily for a fortnight, as investors fret that the government's intention to prioritise immigration controls over access to the single market in exit talks will spark deeper cuts to foreign investment in Britain.
So far, pension funds and other long-term fund investors have responded by buying UK shares and other assets while hedging the currency risk through options and other derivatives that allow them to sell the pound.
That may change if the currency proves too volatile to allow them to fund those trades, and measures of implied market volatility <GBPVOL=> surged yesterday to more than 10 percent for durations out to a year.
Retailer Sports Direct <SPD.L> said the overnight move in sterling, after it had entered into a hedging agreement to protect against weakness in the pound, led to a 15 million pound dent in its full-year earnings forecasts.
"If the rate is $1.20 on average for the remainder of FY17, then the negative impact ... would be in the order of a further 20 million pounds," it said. Shares in Sports Direct dropped over 9 percent, its biggest daily loss since the June 23 vote.