David Cameron was accused by Labour of using "phoney" figures on flood defences, after the national statistics watchdog said Government spending had fallen since the coalition came to power.
Labour leader Ed Miliband said the Prime Minister had been "caught out" in his claim that spending was higher under the coalition than under the previous Labour administration.
The row came as the Institution of Civil Engineers (ICE) urged Chancellor George Osborne to use next month's Budget to restore flood defence spending to its pre-2010 level in his Budget next month, warning that current Government plans provided "neither the level of investment or long-term certainty required to improve resilience against flooding".
At Prime Minister's Questions in the House of Commons, Mr Miliband quoted a letter from the chairman of the UK Statistics Authority (UKSA), Sir Andrew Dilnot to a Labour MP who complained about a claim made in January by Environment Secretary Owen Paterson that the Government was "providing more than any previous Government in the current spending review".
Sir Andrew wrote: "A s at January 2014, Government funding for flood defences was expected to be lower in both nominal and real terms during the current spending period than during the last spending period.
"Our analysis also supports the conclusion that the statement 'over the current spending review period, more is being spent (on flood defences) than ever before' is supported by the statistics if the comparison is made in nominal terms and includes external funding, but it is not supported by the statistics if the comparison is made in real terms, or if external funding is excluded."
The UKSA chair said he had written to Mr Paterson's Department of the Environment, Food and Rural Affairs (Defra) to tell them it would be in the public interest for figures on flood defences to be brought under the Code of Practice for Official Statistics.
Mr Miliband told MPs that Sir Andrew's findings made clear that the Government could claim to be spending more on flood defences only "by ignoring inflation and claiming credit for the money that other organisations, other than government, spend".
The Labour leader said: "The figures the Prime Minister is quoting are phoney and I believe he knows it...
"Why doesn't the Prime Minister admit it?
"They have cut flood defence spending and he has been caught out."
But Mr Cameron responded: "The fact is that if you take the period 2010, when I became Prime Minister, to 2014, the spending has been £2.4 billion - more than the £2.2 billion in the previous four years.
"If you take the five-year period of this Parliament... the spending has been higher than the previous five years.
"These are the facts.
"I have to say to him that having this debate is slightly pointless.
"The whole country should be coming together to deal with flood defences."
But Mr Miliband retorted: "If it is a simple choice between the UKSA and him, people will believe the UKSA."
Labour MP Hugh Bayley, whose complaint prompted Sir Andrew's ruling, said in a statement: "The Labour government increased funding for flood defences from £72 million in 2000, at the time of the big flood in my York constituency, to £646 million when we left office.
"The current Government say spending is at record levels but the actual figures show they have cut the money for flood defences to £533 million - a cut of £113 million since they came to power.
"Owen Paterson, the Environment Secretary, has been playing with figures and this has been confirmed by both the House of Commons library and the UK Statistics Authority.
"After the catastrophic flooding in recent weeks, there is a strong public interest in having accurate and trustworthy figures on Government spending on flood defences.
"I agree with Sir Andrew Dilnot that the in-house figures from Defra are not believable and that figures should in future be quality-controlled and published by the UK Statistics Authority."
But a Defra spokesman said: "Figures on flood defence spending are published.
"The Government is spending £2.4 billion on flood management and protection from coastal erosion, which is more than ever before.
"The figures cited by UKSA are already published in the House of Commons, alongside the figures that show additional spending through partnership funding.
"The Prime Minister also recently announced £130 million extra for flood defence repairs following the extreme weather."
In its submission to the Treasury ahead of the March 19 Budget, the ICE said that Mr Cameron's announcement of £130 million for emergency repairs and maintenance was not enough to make up for cuts introduced in Mr Osborne's 2010 spending review.
The ICE urged the Chancellor to return capital and maintenance investment in flood risk management to pre-2010 levels in real terms.
And it said that ministers should commit to a longer-term investment programme for flood defences beyond the current five-year programme, to provide the certainty needed to improve flood resilience.
ICE director general Nick Baveystock said: "While Government funding for flood risk management rose to £370 million in 2015/16 and is protected in real terms to 2020/21, unfortunately this provides neither the level of investment or long-term certainty required to improve resilience against flooding.
"The reductions to the maintenance settlement are also concerning, and - as the recent flooding and coastal surges have shown - the flood defences protecting our communities, businesses and the other vital infrastructure networks and services we depend on must be maintained regularly and comprehensively."