THERESA May’s day began like any other; full of uncertainty, tension and stoicism.

There was the regular 8am Downing Street breakfast briefing with Julian Smith, the Chief Whip, and other key aides to give a political post-mortem on the drama of the night before and how to get through another Brexit-laden day - without cracking up.

As they patted themselves on the back for escaping the disaster that would have been a Commons defeat on the customs union issue, there was the little matter of the brewing storm over parliamentary “pairing” to cloud the horizon.

Jo Swinson, the Liberal Democrat leader, still on maternity leave, had used the traditional arrangement of pairing with an opposing MP - in this case, Brandon Lewis, the Tory Chairman - to cancel themselves out in key votes on the flagship Trade Bill.

But it transpired Mr Lewis, while abstaining as per the agreement on several votes, had decided to vote in two key ones, including on the knife-edge customs union issue, which the UK Government survived by just six votes; which included the party Chairman’s.

While Tory high command insisted it was a “cock-up,” others sensed a very large and smelly rat.

Ms Swinson was incensed. Mr Lewis personally apologised to the East Dunbartonshire MP, insisting his going through the voting lobbies - twice - had been an "honest mistake" made by the whips in "fast-moving circumstances".

But Ms Swinson was having none of it, complaining it was "neither honest nor a mistake". The row would rumble through the day.

As the dust began to settle on the Prime Minister’s Houdini-style skills of scraping through two very tight Commons votes, the little matter of the final PMQs of the session had to be negotiated.

Always packed out, the atmosphere in the chamber was febrile as Labour MPs expected Jeremy Corbyn to land a few metaphorical blows on what they regard as Mrs May’s increasingly glass jaw.

PMQs began with the nation’s leader paying tribute to the legacy of Nelson Mandela on the 100th anniversary of his birth, noting – with a large dollop of irony in the circumstances – how his message of “forgiveness, peace and reconciliation” was as relevant today as it ever had been.

Yet the first, and arguably most biting barb, came not from the Labour leader but from the Conservative benches as Brexiteer Andrea Jenkyns took aim and asked at what point was it decided “Brexit means Remain”. With friends like these…

As MPs responded with oohs and aahs, the PM rose to declare: “Brexit continues to mean Brexit,” insisting people had to embrace “that bright future,” which quitting the EU would produce.

After clearing a persistent frog in his throat, the Labour leader sought to goad Mrs May by mentioning how some of the Brexiteers in her Cabinet, involved with Vote Leave, had been “referred to the police” by the elections watchdog over referendum spending and urged her to make sure they co-operated with HM Constabulary as they had failed to do so with the Commission.

Clearly angry, the PM urged Mr Corbyn to withdraw the “unjustified…accusation” he had made against individual MPs – he didn’t – but went on to insist that the Brexiteer amendments her Government accepted were all, actually, in the White Paper.

The Labour leader insisted the Government had “sunk into a mire of chaos and division” and denounced her Chequers Plan as a “cobbled-together mishmash”. But his barbs were bouncing off the May armour.

Adopting a Thatcheresque patronising third-person tone, the PM suggested to Mr Corbyn that the point of PMQs was “not that you just read out the question you thought of on Tuesday morning but you actually listen to the answers that the Prime Minister gives”.

She then declared: “The Chequers agreement stands. The White Paper stands. He said we had not even discussed the White Paper with the European Union. I have told him in at least two if not three answers that we are already discussing it with them.”

As the Labour leader insisted UK ministers were not negotiating Brexit because they were too busy fighting among themselves, Mrs May stood up to insist that while he was on a protest march, she was sorting out Nato funding with Donald Trump.

Amid rising noise from baying Labour MPs, she then declared: “While I was delivering a plan for our future trade with the EU, he was delivering a plan to teach children how to go on strike. While I was negotiating our future security relationship with Europe, he was renegotiating the definition of anti-Semitism. He protests; I deliver.”

Having escaped the barbs of Mr Corbyn, the PM seemed most at unease when his Labour comrade Harriet Harman returned to the pairing controversy, suggesting MPs should be able to vote on a draft motion on proxy voting for MPs on baby leave.

“It is time to sort this out. This one is overdue,” insisted the former deputy Labour leader.

Mrs May said, again to expressions of disbelief from opposition benches, that “breaking of the pair was done in error. It was not good enough and it will not be repeated”.

Outside the chamber, her aide was asked how Mr Lewis, having not voted on several votes could then do so twice on the key divisions. “I don’t have anything to add,” he mumbled.

Earlier in the chamber, the whimsical Tory backbencher Keith Simpson praised the PM for her sangfroid in dealing with a “giant ego, somebody who believes that truth is fake news and leaks continually”. He told MPs to laughter he was not referring to Boris Johnson but Mr Trump.

Fortunately for Mrs May just as the straw-haired former Foreign Secretary was standing up to give vent to his Brexit frustrations she was appearing before the grizzled sages of the Commons Liaison Committee.

In the chamber, Mr Johnson, dough-nutted by fellow Brexiteers, issued a rallying call to his party leader to tear up her "miserable" plans for close relations with the EU after Brexit and return to the "glorious vision" of a Global Britain. It was, he insisted, “not too late to save Brexit”.

While he argued the Chequers Plan would mean "Brexit in name only," leaving the UK in a state of "vassalage" to Brussels, Mr Johnson’s resignation statement was not of the Geoffrey Howe vintage; it did not seek to plunge the first metaphorical dagger into the PM’s chest; the threat was implied rather than explicit.

Jacob Rees-Mogg, the pin-striped head of the Tory Brexit faction, gushed about his fellow Brexiteer’s statement, declaring that it was "the speech of a statesman". But opposition MPs, clearly hoping for an “et tu Brute” moment, dismissed the former Secretary of State’s statement as a “damp squib”. Some Tory Remainers had stayed away.

Across in the committee corridor as she waited calmly for a few minutes before being cross-examined by her senior colleagues, Mrs May was pressed by a reporter on whether she would survive in post until the autumn. "I think you know the answer to that,” she snapped.

After answering questions from Brexit to Nato and defence spending, the PM emerged unscathed from the Liaison Committee and headed for the uncertain embrace of the Tory 1922 Committee.

Cheers went up and tables were banged as Mrs May sought to restate her case and rally the troops for the battle with Brussels ahead.

Of course, the battle on this side of the Channel might still be the harder. Indeed, ardent Brexiteer Steve Baker, the former Brexit Minister who resigned over the Chequers Plan, raised the prospect of a leadership challenge, which requires 48 signatures to trigger.

"A number of 40 has been bandied around in this House in the last few days…It gives me no pleasure to say it but the thing I have to say is 'and the rest.’”

But one rebel MP, Simon Clarke, who represents Middlesbrough South, stood up to tell the ’22 he had withdrawn his letter calling for a confidence vote in Mrs May.

“God knows,” he declared, “the threat of a Corbyn government is real. We’ve looked into the abyss in the last few days…We should just not do this.”

Brexiteer Iain Duncan Smith, who understands the vicissitudes of being his party’s leader, suggested it possessed an “inner gravity,” which was pulling it back together in the face of the threat from the chief comrade, Jeremy Corbyn.

A colleague claimed Mrs May’s ’22 appearance had been a “triumph” while another calibrated she had “done enough” to survive.

By early evening, the PM was back in Downing Street having to glad-hand, of all people, a gaggle of exhausted Lobby journalists, assessing her language and demeanour over a glass of warm white wine.

The embattled party leader appeared on good form; no doubt more relieved than anything that, after 72 hours of riding the Brexit rollercoaster, she had survived intact.

Today, she will seek political comfort in, of all places, Northern Ireland, visiting the border to reinforce her Brexit message and pronounce once again her devotion to “our precious Union”.

When asked if she could sum up her feelings after a week from hell, the PM jokingly told one reporter: "For you? My feelings for you?” before adding: “We all need a break." Indeed, we do.

A soothing walking holiday with husband Philip in the Swiss Alps beckons but once she comes down from the mountain-top, in September the Brexit rollercoaster ride will start all over again.