The FTSE 100 was down 93.56 points, or 1.3 percent, at 7,010.42 points at 1452 GMT, retreating from a record high of 7,122.74 hit on Monday.
The index extended losses in afternoon trade after a private sector report showed that U.S. consumer confidence unexpectedly slumped in April.
The FTSE is up 6.7 percent year to date, tracking a rise across Europe on the back of the European Central Bank's asset purchase programme and better economic data out of the euro zone.
"There'a a bit of bad news," said Andy Ash, head of sales at ADM Investor Services International. "It's just a bit of froth (being taken) off the market."
The FTSE was also dampened by Asia-focused bank Standard Charted, wealth manager St James's Place and Costa Coffee-owner Whitbread after their updates.
Standard Chartered fell 3.5 percent after saying profits in the first quarter of 2015 fell by over a fifth from a year ago as losses from bad loans jumped and trading conditions remained challenging.
St James's Place also retreated 3.5 percent after posting slightly below forecast inflows in the first quarter. Whitbread shed 2.4 percent after its chief executive announced plans to leave by February next year.
AstraZeneca slid 3.3 percent after U.S. rival Merck & Co's diabetes drug met heart-safety requirements in a recent study, giving it a leg-up on the UK group.
Traders said the FTSE could struggle to make headway ahead of the closely contested British election on May 7. Sectors such as utilities and banks could come under regulatory pressure if the opposition Labour party takes office.
No party is expected to win an outright majority.
"As we get closer we’re going to get a bit more volatility but people who hold equities for the long term shouldn’t be distracted by short-term political risk because you just don’t how that will play out," Ian Williams, a strategist at Peel Hunt, said.
Centrica, which has underperformed along with other domestic utilities this year due to Labour's plans to cap bill rises, gained 2 percent after its chairman said it had made preparations in case it is approached with a takeover offer.
(Reporting by Francesco Canepa; Editing by Mark Heinrich)
By Francesco Canepa and Alistair Smout
