Jeremy Hunt warned over hospital waiting times data

Health Secretary Jeremy Hunt has been warned by the UK's statistics watchdog over claims he made about accident and emergency waiting times in England.

Sir Andrew Dilnot said Mr Hunt was wrong to claim in the Commons that median waiting times to be seen in A&E departments had halved since 2010.

He said the health secretary "may wish to take advice on whether he should correct the parliamentary record".

Labour said that Mr Hunt had been "found out making dodgy claims".

But a government spokesperson said it had "simply been a slip of the tongue on Mr Hunt's part and that the numbers used by him and the prime minister were accurate".

The Conservatives and Labour have been involved in an increasingly rancorous fight about each other's records on the NHS in recent months, with David Cameron and Ed Miliband clashing on the issue on several occasions at Prime Minister's Questions.

Sir Andrew, chair of the UK Statistics Authority, has now responded to a Labour complaint about the use of statistics by the prime minister and Mr Hunt on accident and emergency waiting times in England.

Mr Cameron told the Commons on 2 July that the average wait for an A&E assessment had more than halved from 77 minutes under the Labour government to only 30 minutes under the coalition.

A week later, Mr Hunt repeated the same statistic but specifically referred to a "median wait".

Sir Andrew did not criticise the prime minister but said the health secretary should have used the term "mean" instead of "median".

He said the statistics showed that the mean time elapsing before patients were assessed was 30 minutes in 2012-13, down from 77 minutes in 2009-10. On the other hand, the median wait for assessment fell from nine minutes to eight minutes over the same period.

The mean is calculated by adding up all the numbers and dividing by the number of numbers. The median is the number for which half the numbers are above and half below.

Analysis by Health Editor Hugh Pym

The debate over waiting times in accident & emergency units in England is already highly charged - and it will be even more so as the election approaches.

That's why a rather dry looking letter from the statistics watchdog Sir Andrew Dilnot has some significance.

In essence, he is saying the Health Secretary Jeremy Hunt was wrong to tell the Commons that "median" waiting times to be assessed had fallen under this government from 77 minutes to 30.

What he meant was that the "mean" had come down over that time.

As it turned out the median - seen by some statisticians as more relevant when dealing with data which includes some extreme values - had only come down from nine minutes to eight.

Sir Andrew, in effect, dismisses the relevance of "time to assessment" in A&E - a benchmark used by both the Prime Minister and Mr Hunt.

He says that the "most complete" account of waiting times is time to departure rather than first assessment.

On that basis median waits are up from 122 minutes to 128. If all this sounds technical, it is.

But it adds important detail to an intensifying debate.

In a letter to shadow health secretary Andy Burnham, circulated to Mr Hunt and Mr Cameron, Sir Andrew said data on A&E waiting times data was "complex", with both the median and mean figures being referred to in official statistics.

But he added: "Statistics are often described in abbreviated terms, particularly during public debate, and caveats are not always repeated or indeed possible.

"However, it is important for statistics to be described carefully.

"Where possible, time periods should be specified, the source data should be identified, and particular care should be taken if the mean and median are substantively different."

But Mr Burnham said it was not the first time that ministers had been "found out making dodgy claims about the NHS" in Parliament.

"Sir Andrew Dilnot confirms that waiting times in A&E have got worse on this government's watch," he claimed.

"But his analysis concludes that things are even worse than we thought, with hospital A&Es missing the government's lowered target in every quarter for almost two years.

"This is a damning verdict on David Cameron's and Jeremy Hunt's mismanagement of the NHS and their desperate attempts to paper over the cracks.

"The gap between their spin and the reality for patients is becoming dangerous."