Theresa May and Andrea Leadsom "breached the ministerial code" by unwittingly misleading MPs over the pairing controversy, Labour have claimed.

Shadow Commons Leader Valerie Vaz said the Prime Minister and Leader of the House fell short of the standards expected of ministers by characterising Chief Whip Julian Smith's action as an honest mistake.

Mr Smith ordered Tory Party chairman Brandon Lewis to break a pairing agreement with an MP on maternity leave during a crucial Brexit vote last week, but Mrs May said he had made an "honest mistake" and had apologised.

He had been "paired" with Liberal Democrat deputy leader Jo Swinson, meaning neither would walk through the voting lobbies.

Ms Vaz, speaking during an urgent question on pairing arrangements, told the Commons: "The answers and the statements made by the Prime Minister and the Leader of the House on the 18th July confirmed that the Government Chief Whip was less than candid with his fellow ministers, including the Prime Minister, by not declaring that he actively instructed Conservative MPs to break pairing arrangements.

"It's clear that the Prime Minister and the Leader of the House have unwittingly misled the House by characterising the Government Chief Whip's action as an honest mistake.

"This is a serious breach of the ministerial code."

Earlier, Liberal Democrat Chief Whip Alistair Carmichael, asking the urgent question, said he was "disappointed" Mr Smith was not responding.

He said: "There are serious questions still outstanding about the events of last Tuesday evening and the only person who knows the truth about them is the Chief Whip himself.

"There is a serious lack of confidence today in the system by which we run our business, and the only person who can restore that confidence is the Chief Whip."

Mr Carmichael added: "It may have been a mistake to cancel the pair, but it was not an inadvertence - it was a deliberate act."

Cabinet Office Minister David Lidington said it was "perfectly appropriate" that he answer the question, and told the Commons the Government was "committed" to providing a pairing system as he sought to reassure MPs that "the errors of last week will not be repeated".

And he said Mr Lewis did not know he was paired with Ms Swinson, adding: "He should not have been asked to vote, an error was made within the Government whips' office, for which (Mr Smith) has taken responsibility - hence his public apology to (Mr Carmichael) and to (Ms Swinson)."

Mr Lidington said there was not "some sort of deep-laid plot to deny the pairing arrangement", and told MPs: "Neither the Prime Minister nor the Leader of the House were consulted about the matter and the Government policy remains that pairing is an informal and voluntary arrangement between the political parties - we do take the issue of pregnancy pairing particularly seriously for the very reasons that have led both the business committee and then the procedure committee to highlight this as something which the House ought to address, and that is why we will be taking forward the debate on proxy voting in September."

Peter Bone, Conservative MP for Wellingborough, demanded greater transparency and called for a public list of pairing arrangements.

"The problem is that until I came to this chamber today I had no idea there had been 2,000 pairs since the general election," he said. "It's done behind closed doors and in secret.

"If this pairing system was public and each day the people who were paired were listed - and in fact maybe even removed from the possibility of voting - then this would never occur again.

"What we need is transparency and I hope the Deputy Prime Minister will look into this matter."

However, Mr Lidington flagged up the need for privacy for MPs who may be suffering health issues and insisted it was "not always right" for the arrangements to be made public, adding: "I do think, despite what he says, it is best for these matters to be left for informal agreement between the usual channels."

Meanwhile, Labour MP for St Helens North Conor McGinn unsuccessfully called for the vote to be re-run, citing the precedent of a similar pairing breach when James Callaghan was prime minister in 1976.

"He and the then leader of the opposition decided the only way to resolve matters was for the chief whips to meet and the vote to be re-run," he said.

"Precedent has been set. When will the Government show the integrity I know he and many colleagues opposite possess in abundance?"