Downward revisions to official statistics show output fell 2.4% in the first three months of the year and the recession started three months earlier than thought

The recession facing Britain is even deeper than had been thought and started more than a year ago, it was revealed today.

National income fell in the first quarter of this year by 2.4%, the biggest drop since 1958, as the Office for National Statistics revised its initial estimate of 1.9%.

The figures are much worse than expected. Extended to the whole year, the drop in output in the January to March period is now equal to 4.9% – the worst since records began in 1948.

"We hope the recovery comes as soon as possible but sadly we now know this recession has been longer and deeper than we had thought," said shadow chancellor George Osborne.

"This also means that in the future unemployment will be higher and Labour's debt crisis will be even worse."

Although GDP fell 2.4% in the third quarter of 1979 and first quarter of 1974, statisticians said these were rounded from 2.36% or 2.37%. The figure for this year was exactly 2.4%.

The revision is one of the biggest ever made by the ONS and it said the reasons were changes to its estimate of the construction and services sectors.

The ONS also revised down its figure for the second quarter of last year to -0.1% from zero, meaning the recession started earlier than previously thought. And the fourth quarter of 2008 figure was revised down to a fall of 1.8%.

"The recession, which now begins in the second quarter of 2008 rather than the third, is now thought to be quite a bit deeper than previously thought, and is looking ominously like the early 1980s vintage," said Danny Gabay of Fathom Consulting.

Critics of the Bank of England who called for big interest rate cuts in the first half of last year, will feel justified by the data, since the Bank's monetary policy committee argued into last autumn that there was little likelihood of a recession occurring and delayed rate cuts until October. In fact, the economy had entered one last spring.

Separately, the Trades Union Congress said that while there were signs of "green shoots" in the economy, this was more to do with an easing of the pace of the fall in output rather than that a big recovery was under way.

"This recession is already worse than the 1990s one and is likely to be worse than that of the 1980s," said Richard Excel, TUC labour market expert. "It has been very severe and we are probably only half way through. It will be quite some time until employment and growth return to pre-recession levels."

Paul Gregg, labour market expert from Bristol University, noted that unemployment had started rising earlier in this recession than in previous ones and was "encouraged" that monthly rises in the claimant count appeared to be slowing down.