Theresa May has insisted her chief whip was not trying to steal votes in knife-edge Brexit showdowns despite him apparently confessing to breaking Commons convention.
Julian Smith has not denied ordering Tory MPs to ignore pairing arrangements designed to help sick or pregnant MPs to miss votes sparking calls for his resignation.
Quizzed on the controversy in Belfast, the prime minister was asked why she had not sacked him for effectively trying to steal votes from the opposition.
A Tory backbencher has said Mr Smith all-but admitted to her that he issued the order, which led to Brandon Lewis, the party chairman, voting when he was paired not to.
But Ms May replied: There was an honest mistake made for which the chief whip and, indeed, Brandon Lewis have both apologised.
The prime minister did not respond to the questioner inquiring if she endorsed his conduct, amid questions about how much she knew in advance of the votes.
An answer she gave to MPs on Wednesday appeared to imply that an error was made only in relation to Mr Lewis, who’s pair was Liberal Democrat Jo Swinson, a new mother.
The others ignored the instruction, after further advice, but Mr Lewis did break his pair accidentally he has insisted.
In Belfast, after a one-sentence answer about the row, a clearly uncomfortable Ms May immediately switched to talking about her Chequers plans to break the Brexit deadlock.
Labour said her response defied belief, calling for Mr Lewis and Mr Smith to resign and for the prime minister to find the strength to sack them if they refused.
It is unbelievable that the prime minister has repeated the desperate and blatantly untrue excuses made by her party chair and chief whip, said Tom Watson, Labour’s deputy leader.
This is about public trust in politics. At such a crucial time for our country, people expect candour and decency, not cowardice and dishonesty.
Therefore I can only conclude MPs were told to break pairs on Tuesday, she said. I refuse to be tarnished by this behaviour so will not stand by and say nothing.
Mr Smith is also believed to have admitted to a rival chief whip that he told Mr Lewis to break his pair apologising only because he didn’t realise it was with someone on maternity leave.
Pairing allows MPs on different sides to agree not to vote so that absences for a variety of reasons also including travel away from Westminster do not change the margin of results of votes.
The positions of both Mr Smith and Mr Lewis appear safe while No 10 following a rash of cabinet resignations is determined to stand by them.
However, the chief whip will continue to face pressure to end his silence and explain what happened, when MPs return to the Commons on Monday.