The British economy contracted at a much sharper pace than initially thought and at its fastest rate in more than 50 years in the first three months of this year, official data showed on Tuesday.

The Office for National Statistics said GDP fell by 2.4 percent in the first quarter, revised down from a fall of 1.9 percent.

That was the biggest quarterly rate of decline since Q2 1958 and worse than analysts' predictions for a fall of 2.1 percent.

On the year, GDP fell 4.9 percent -- the biggest decline on record. The ONS had previously estimated a fall of 4.1 percent. Back data were also revised down, meaning Britain's recession started in the second quarter of 2008, earlier than thought.

Recent data have suggested that the economy may already be picking up-- the Nationwide building society said on Tuesday house prices rose for the second month running in June.

But policymakers remain cautious about declaring victory over Britain's worst recession since at least the early 1980s and the GDP data may raise concern that the economy is even weaker than previously feared.

"To that extent I think it will keep the Monetary Policy Committee cautious about withdrawing stimulus from the economy," said Amit Kara, economist at UBS.

The Bank of England has cut interest rates to a record low of 0.5 percent and embarked on an unprecedented 125 billion pound quantitative easing programme to support the economy and most analysts expect monetary policy to remain ultra-low for a while yet.

The ONS said the extremely large revisions were a result of changes to the methodology of calculating construction and also lower services output, which each contributed around half of the 0.5 percentage point downgrade.

"The figures are disappointing. We knew about the construction revisions in advance and the fall wasn't quite as big as the ONS had indicated," said Ross Walker, economist at RBS Financial Markets. "But we've got a much bigger fall in services output."

Separately, the ONS released data on the balance of payments.

Britain's current account recorded a deficit of 8.540 billion pounds in the first quarter, a much bigger deficit than the 6.8 billion pound gap forecast by analysts. That followed a deficit of 8.771 billion pounds in the final quarter of 2008, which was more than 1 billion pounds bigger than previously estimated.