Labour today accused David Cameron of giving Parliament misleading information over his proposals for a tax break for married couples, and demanded that he come back to the House of Commons to correct statements made during Prime Minister's Questions.
The Prime Minister told MPs that "all married couples paying basic rate tax" will benefit from the tax break, which is in fact available only to basic rate taxpayers whose spouses or civil partners do not work or earn less than the income tax threshold of around £10,000.
When shadow chancellor Ed Balls challenged the claim in a point of order, the PM amended his wording slightly to say that the transferable tax allowance will be "available to every basic rate taxpayer".
Downing Street aides later said that Mr Cameron had been drawing a distinction between the planned tax break being available to basic rate taxpayers but unavailable to those paying the higher rate, and "did not go into the fine detail of the policy in the Commons".
But a senior Labour source said: "The Prime Minister was totally wrong. The Prime Minister clearly doesn't understand his own policy.
"The Treasury website clearly states that the policy benefits married couples, including same-sex married couples and those in civil partnerships, where one is a basic rate taxpayer and one has unused personal allowances. The Institute for Fiscal Studies says it will not be available to 69% of married couples.
"The Prime Minister was not only wrong, he is so out of touch that he lives in a world where he thinks all women do is stay at home.
"Ed Balls rightly used a point of order to try to make sure the Prime Minister corrected the record. We will be writing to say that the Prime Minister must come back and correct the record. This is simply wrong and must be corrected."
Downing Street sources said that the Government had always made clear that the tax break could be claimed only where one partner is not using his or her personal allowance either because they are not working or is on a low income.
But a source added: "In the Commons, he didn't get into that small print detail. It's not available to people on higher rate tax, which is the key point."
Mr Cameron was first challenged over the married tax break by Labour MP Tom Harris during the regular weekly session of Prime Minister's Questions.
The PM said: "What I can confirm is that all married couples paying basic rate tax will benefit from this move.
"I will tell you why I think this is important - it is not about the money, it is about the message. I think marriage is a great institution and I think we should be supporting marriage through the income tax system."
Labour MP Kate Green later cited predictions that 83% of the money paid out under the scheme will go to husbands and just 17% to wives, asking the PM why he had such a "blind spot when it comes to women".
Mr Cameron responded: "I think it is worth supporting marriage through the income tax system.
"Let me make this challenge: in government, Labour gave a marriage tax break through the inheritance tax system. They gave a married tax break to the rich. I want to give a married tax break to everybody."
But Mr Balls said the Prime Minister was wrong to claim the move would benefit all married couples paying the basic rate of tax.
Raising a point of order, the shadow chancellor said: " The Prime Minister said that all married couples that are basic rate taxpayers would benefit. Would the Prime Minister like to correct the record, because that is just not true?"
After he was i nvited to respond by Speaker John Bercow, Mr Cameron changed his wording slightly and said it would only be "available" to married couples paying the basic rate of tax.
He said: "The point is the married couples allowance is available to every basic rate taxpayer.
"I think that is something to celebrate in our country. I stand up for marriage, even if you want to talk it down."
The tax breaks for married couples worth up to £200 a year will be introduced from 2015.
Under the scheme, married couples - where one half earns less than £42,285 and the other earns less than the personal allowance threshold - will be able to switch up to £1,000 from that unused personal allowance to their other half that pays the basic rate of tax.
In a letter to Mr Cameron, Labour's shadow Treasury chief secretary Chris Leslie told the Prime Minister that his claim that "all married couples paying basic rate tax" would benefit was "absolutely false".
And Mr Leslie said that it was "clearly absurd" for the PM to state that the transferable allowance will be "available" to all basic rate taxpayers.
"This is clearly an absurd claim to make," said Mr Leslie. "The Marriage Transferable Tax Allowance is only available to basic rate taxpayers whose partners have unused personal allowance. According to HM Treasury, just four million married couples in this situation will benefit - compared to 8.9 million married couples where there is a basic rate taxpayer."
He added: " I would be grateful if you could correct the record, and confirm the following: Not all married couples paying basic rate tax will benefit from the Marriage Transferable Tax Allowance; Most married couples will not benefit from the Marriage Transferable Tax Allowance; The Marriage Transferable Tax Allowance is not available to every basic rate taxpayer."
Mr Cameron's official spokesman told reporters at a regular Westminster briefing: "The point the Prime Minister made was that it is available to all basic rate taxpayers who are married to transfer unused tax allowance. That was the point he was making."