Interview: Chief Whip Gavin Williamson MP on his factory worker beginnings and recent promotion

It was in that trade where he became known as 'the baby-faced assassin', a nod to both his boyish looks and his capacity to crack the whip when necessary.

The trait has served him well in his career in politics, and he will be calling on that particular skill set more than ever in his new role as Government Chief Whip.

"There is a correlation between what I've done in the past and my political career," says Gavin, speaking after his Downing Street appointment on Thursday.

"In business you often end up in tricky situations where difficult decisions have to be made.

"My roles in politics have been similar in some respects. It's about getting things sorted out and then smoothing things over. After a while you get into a groove."

Recently the South Staffordshire MP has been more of a kingmaker, marshalling Theresa May's path to Number 10 as her campaign manager on the back of a three-year stint as one of David Cameron's closest aides.

Gavin says he was 'devastated' when Mr Cameron resigned on the morning of the EU referendum result, although he had known privately for months that it was going to happen if the Leave camp won.

The pair spent the last throes of the referendum vote awaiting the result in Number 10, two speeches at the ready, one for each possible outcome.

"There was no way that David could state publicly that he was planning to step down if the result went against him," he said.

"The debate would then have been all about him, rather than this vital decision over our membership of the EU. It was the last thing he wanted to happen."

Gavin wasted little time in making his next move. He admits he was in a 'glum' mood the day after the referendum.

It was his 40th birthday, the first few hours of which he spent mulling over his 'thoroughly enjoyable' run as Mr Cameron's parliamentary private secretary.

But as is often the case with Gavin, he had a plan. "At the time everyone's favourite was Boris Johnson," he recalls.

"I just couldn't see it. I knew Theresa was by far the best person for prime minister. She had the right tools for the job.

"Everyone told me I was wrong and that she couldn't possibly win, but I sensed the mood of the country. People were looking for someone who is a serious politician who can make tough decisions in challenging times.

"I just knew instinctively that she was the one."

It was a view, he says, that he formed as a direct result of witnessing Mrs May in action both in the Commons and in private meetings with Mr Cameron.

"She is the only Cabinet minister that I've seen have four meetings with the Prime Minister over the same issue and turn him down every time," Gavin says.

"I had been sent to deal with her several times and always found her nice, kind and decent, but when she thinks she is right she is completely and utterly unmoveable."

That same day he called Mrs May and told her he wanted to help with her campaign, and 24 hours later he was offered the post of parliamentary campaign manager.

"I was absolutely flabbergasted, but I accepted immediately," says Gavin. "I was ready to get to work.

"I've also worked with the other candidates. I had a good idea of what makes people tick."

His task was to rally as much support for Mrs May among fellow MPs as possible. "We had very little time and no infrastructure," he recalls.

"It was a case of, right, what do we need to do and how can we get it done quickly?"

He gathered a small group of MPs together, including Julian Smith, Kris Hopkins, Simon Kirby, Karen Bradley and George Hollingberry, and worked out who they needed to target.

"Some MPs were easier to persuade than others," Gavin explains, a wry smile spread across his face.

But the hard work paid off, with Mrs May polling more than 60 per cent in the second round of voting, after which Michael Gove was eliminated.

It was that strength of support that played a big part in Andrea Leadsom's decision to pull out of the race, just moments after Mrs May had finished a campaign speech in Birmingham on Monday.

Gavin says he was shocked at the abrupt end to the campaign. He said: "We had been planning for the long haul, expecting to be working away behind the scenes until September when the vote was due to take place.

Now his thoughts have turned to the next stage of his career. The move to Chief Whip is a huge promotion. It will see him move to Number 12 Downing Street and also attend Cabinet meetings.

As a loyal servant to the Conservatives, who has never voted against the party, he is in prime position to tackle the seemingly daunting task of keeping the divided Tory hordes in check.

He is far from your average Tory, having grown up in Scarborough and been educated in a comprehensive school. He even had a stint working at what he describes as a 'metal bashing' firm.

But for a measure of how far he has come in the world of politics, go back to 2013 when the Speaker of the Commons, John Bercow, gave him a dressing down for being too loud during Prime Minister's Questions.

"His role," the Speaker said, "is to nod his head in the appropriate places, and to fetch and carry notes – no noise required."

Three years later and Gavin is well on his way to becoming a big noise in politics.

By Pete Madeley