Britain's economy is still growing, but it grew much slower in the first quarter of 2015 than it did at the end of last year.
Official figures show that GDP grew by 0.3% between January and March this year - half as much as it grew between October and December 2014, at 0.6%.
This is the weakest quarterly growth since the end of 2012 - and with the General election just nine days away, this will be seen as a major setback for the government.
The ONS puts the blame on a slower service sector, a shrinking construction industry, and a slight squeeze on industrial production caused by lower oil and gas prices.
ONS chief economist Joe Grice said: "As always, we warn against reading too much into one quarter's figures."
The Prime Minister has said that today's just-released GDP figures show that "our economy is still growing" and that "we can't take the recovery for granted".
GDP figures show our economy is still growing, but we can't take the recovery for granted. Don't risk it with Ed Miliband and the SNP.
Mr Cameron was responding to figures showing slower economic growth in the first quarter of 2015 than in the last three months of 2014.
After the ONS released slower-than-expected figures on Britain's economic growth, George Osborne has insisted that the "future of the economy is on the ballot paper".
GDP figures show future of the economy is on the ballot paper. We should stick to the plan that's delivering a brighter more secure future
Figures show that the economy grew by 0.3% in the first quarter of 2015 - half as much as the 0.6% it grew between October and December 2014
With rising instability abroad, now is worst possible time to vote for instability at home.
The UK economy grew by 0.3% during the first quarter of 2015, the Office for National Statistics said today.
Official figures released today are expected to show that the UK economy's growth slowed down in the first three months of 2015.
GDP rose by 0.6% in the last quarter of 2014, but economists say they expect the figure to be around 0.5% between January and March this year.
Some experts blame this on the global fall in oil prices, while construction has shrunk and exports are also down.
Deputy Prime Minister Nick Clegg said the economic recovery "wouldn't have happened" without the Liberal Democrats being part of the government.
Speaking to ITV News' political correspondent Carl Dinnen, the Liberal Democrat leader said: "You can't create an economic recovery without having a stable government.
"The Conservatives wouldn't have been able to do it without the Liberal Democrats, the Liberal Democrats wouldn't have been able to do it without the Conservatives."
Two thirds of British adults say that despite the economy growing they don’t feel better off, an Comres poll exclusive for ITV News has found.
While George Osborne has hailed GDP's return to pre-crisis figures as a "milestone", 69% of people interviewed said they do not feel wealthier - while one in four (24%) said they currently spend more than they earn each month.
Although only 35% of Britons said their personal finances are getting worse (the joint lowest since 2010), only 14% said they are getting better. Instead, most said they are about the same (52%).
A majority of the 2,035 Britons interviewed (55%) also agreed the improving economy is only benefitting the rich, while three in five (62%) think the gap between rich and poor has got worse over the past three months.
Prime Minister David Cameron said the GDP growth figures released today are a "major milestone" in the government's plan for the economic recovery, thanks to the "hard work of the British people", but warned "the work isn't finished yet."
Chancellor George Osborne said GDP figures on growth show that his economic recovery plan is working, but not complete and that he wanted people from all parts of the country to feel the impact of the recovery.
Speaking to Economics Editor Joel Hills from Newcastle he blamed the previous government for the three year delay in a return to growth figures, saying it takes time to work through problems caused when governments "get economic policy wrong".