The people who got to the top on a four-day week

For Marc Nohr, being a part-time boss means he can spend more time with his family and on charity work.

He is one of about a million people in senior or manager-level jobs who work part time, a number which is growing, according to official figures.

Mr Nohr, who as group chief executive of agencies at Miroma runs a group of marketing and communications agencies, started working four days a week two years ago when he found his hours had become "unsustainable".

But he admits that not everyone is on board with his decision, noting that the very phrase "part-timer" is considered by some to mean "slacker".

"I have to be careful depending on who I am speaking to. Some people come from an era of presenteeism.

"If that's the world in which you were brought up, then it will require quite a bit of a mental leap."

Using data from the Office for National Statistics, consultancy Timewise, which promotes flexible working, found that the number of part-time workers in senior level positions last year was up 55% since 2012.

It used those with a full-time equivalent salary of £40,000 a year to determine who qualified as a senior or manager-level employee. The consultancy credited changing attitudes towards flexible working for the shift.

"Just a few years ago, people were reluctant to admit they worked part-time for fear of being seen as less committed or ambitious," says Timewise co-founder Karen Mattison.

However, it says part-time work for the most senior roles is still relatively rare.

Of his old routine, Mr Nohr says : "There were days when I was getting in at seven or eight in the morning and I was still in at midnight."

Not only was the "always-on culture" hugely detrimental to family life, he says it was also harming his productivity.

To begin with, he asked his employers if he could test out his part-time regime for a trial period. He also came up with a plan on how work would be done in his absence.

In general, he says his employers have been very supportive. It also helps that other staff in the company at his level have the same arrangement.

However, he accepts there are risks involved and says having boundaries in place is important - as is making sure his colleagues know what he is up to.

"Nobody has the right to call me on a Friday because I don't work on Friday. But if you have to, you go in," he says, with regards to workplace emergencies.

Katie Bickerstaffe is another person at the top who works part time. She will soon start a new job at Marks & Spencer, where she's currently a non-executive director. From April she will work four days a week as chief strategy and transformation director.

"From the get-go I said I would want to do that on a flexible basis," she says. "Nobody fell off their chair."

She says that earlier in her career she worked for Dixons Carphone as chief executive for UK and Ireland, also for four days a week.

"When Dixons talked to me about doing the job, I said I was flattered but I need to do it four days a week because at the time my children were very young," she says. "They didn't make a big thing about it and they were respectful."

Like Mr Nohr, she says you have to be "realistic" about dealing with problems on your days off. But the motivation of free time in exchange for good time management can work wonders for morale, she says.

As to why part-time bosses aren't more common, she again blames a culture of presenteeism at some firms, but also a "fear of loss of control" among some managers.

As for employers, she thinks that those that are flexible will get to pick from a wider pool of talent.

"This is something worth sticking your neck out for because you do get rewarded," she says. "You get the pick of the people, huge loyalty and people are thrilled to have the opportunity."