Supermarket stocks were sharply lower after new industry figures showed the grocery market grew at its slowest rate for 11 years.
The latest data from Kantar Worldpanel revealed that Tesco, Sainsbury's and Morrisons all lost market share over the last 12 weeks as competition from the discounters Aldi and Lidl intensified.
All three companies were lower in the FTSE 100 Index, which closed down 2.1 points at 6796.4 amid ongoing tensions in Ukraine.
The pound was just below 1.70 against the US dollar - its highest level for nearly five years as traders bet an improving economy will spur the Bank of England to increase interest rates sooner than it currently predicts.
In contrast, US Federal Reserve chairman Janet Yellen expects low borrowing rates will continue to be needed for a "considerable time".
She told Congress the US economy is improving but noted that the job market remains "far from satisfactory" and inflation is still below the Fed's target rate. Sterling held steady against the euro at 1.22. Market heavyweight HSBC contributed to the FTSE 100's decline after it reported a slide in first-quarter profits due to weaker earnings in Asia and from its investment banking division.
HSBC was 7.6p lower at 596.5p, while Barclays fell 1.7p to 243.3p and Lloyds Banking Group dropped 1.8p to 76.7p in a tough week for the banking sector.
Credit-checking firm Experian was the biggest faller in the top flight after forecasting subdued trading in the first half of the financial year due to headwinds such as the World Cup on business in Brazil. Shares fell 74p to 1060p.
Morrisons fell 11.2p to 190.8p and was joined on the fallers board by Sainsbury's after the rival chain surrendered an initial rise seen in the wake of annual profits at the top end of City expectations. Shares in Sainsbury's were up by nearly 2% at one stage but later closed 9.5p lower at 323.9p following the Kantar figures and expectations that the group will post lower profits in the current financial year.
Tesco shares were 1.8p lower at 286.1p.
Elsewhere, shares in ITV lifted 1.6p to 187.5p after it unveiled a deal to acquire a controlling stake in Pawn Stars-maker Leftfield Entertainment, which produces more than 300 hours of programming a year for more than 30 US networks.
Shares in low-cost airline easyJet were 43p higher at 1710p after it said it carried more than 5.78 million passengers last month - a 10.2% increase on the total for April last year.
The biggest FTSE 100 risers were G4S, up 9.9p at 250.2p, Legal & General, up 6.5p to 220p, easyJet, up 43p to 1710p and BAE Systems up 7.1p to 404.5p.
The biggest fallers were Experian, down 74p to 1060p, and Morrisons, down 11.2p to 190.8p.