According to Karren Brady, at the very top "one of the hardest things you have to do is say 'no' sometimes". Yet during the course of 20 years in football, the mother and writer best known for her role as managing director of Birmingham Football Club earned a reputation as "a sacker". Now Brady, 44, is gearing up to employ her formidable skills once more as Sir Alan Sugar's sidekick when The Apprentice returns tomorrow night on BBC1.

Reflecting on her reputation, Brady, who has two children, claims she has "mellowed": "When you're younger you're far ballsier and you want to get things done," she says. "You mellow and change over the years as you employ more people."

Back when she was appointed managing director at Birmingham aged 23, things were different. No sooner did she take over than she started getting rid of most of the club's existing staff.

It was a case, she says, of "either do it or the business is going down the toilet, so you've got to man up and do it...

"I inherited that very poor state of a business and it was a case of changing that business or trying to win a personality contest… There was not the clear direction, there weren't the right people with the right skills doing the right jobs."

The mother-of-two was 27 when she had her first child, Sophia, 17 years ago. "Back then phrases like work-life balance and flexible working hadn't been invented," she says. Not least in the male-dominated world of football, her turf for 20 years.

"I took it as my personal responsibility to be able to juggle. I didn't want anybody to help me and I didn't expect my office to make it easy for me," she says. Indeed, Brady – who is dressed for business in a blue silk shirt, pencil skirt and vertiginous spiked black Chanel-embossed heels – returned to work just weeks after the birth of her son, Paolo.

Brady is keen to admit that having it all sometimes means "not always getting it right". Now that her children are 17 and 15, she says they physically need her less (even if "the problems children bring get bigger as they get older"). But she has always been realistic about what she can expect to achieve.

"When I was younger I just accepted that I could only do what I could do, and yes it's true that I didn't always drive them to school and I didn't always pick them up from school but I take responsibility for their moral outlook, their self-esteem and their confidence. No one can claim that more than me."

"Those are the things women have to accept. You take responsibility for your children but you're not always the taxi driver and that doesn't make you a bad parent."

Part of her job as a mother, Brady says, is setting an example. "Working hard, being responsible, going out to get the things that you want. No one else can teach your children that."

Born in Edmonton, north London, she is the daughter of Terry Brady who made his fortune in printing and property development and was a former chairman of Swindon Town and a director of Portsmouth. Karren went to boarding school and went on to marry Canadian footballer Paul Peschisolido in 1995.

She joined Birmingham in 1993 after starting her career as a graduate trainee with advertising agency Saatchi & Saatchi – having fibbed on her job application in which she said she had a degree – and moving on to a rather successful foray in sales at the London Broadcasting Company, where she made more commission than the rest of the team put together.

As well as replacing Margaret Mountford in 2010 as a co-adviser to Lord Sugar on the series, Brady is on the board of Philip Green's clothing empire Arcadia, writes a column for Woman & Home magazine and The Sun and has published four books including two novels. Just reading through her raft of achievements in the football field alone (she is currently vice-chairman of West Ham United) is quite exhausting.

It is some comfort to hear that her book Strong Woman: Ambition, Grit and a Great Pair of Heels was delivered two years late. According to the synopsis, the book charts "how she went on to persuade David Sullivan, at the age of 23 to buy a football club – turning that business round to sell it for an incredible £82m 12 years later". She also discusses the moment when, aged 36, she was told that she had a cerebral aneurysm and spent 24 hours in intensive care before undergoing a risky operation.

"I found it very difficult to write because it's very difficult to go back into your memory and pull out things," she says. "From nowhere eventually things start coming back, but it was two years overdue and I'm not in a hurry to write another one."

While she won't comment on the recent tribunal in which previous Apprentice winner Stella English unsuccessfully claimed constructive dismissal by Lord Sugar, when it comes to judging the contestants, Brady concedes, sometimes "you think you've got their cards marked but you don't".

This series, viewers can expect the usual formula: self-assured would-be (and sometimes established) entrepreneurs vying to become a business partner of gruff business tycoon Alan Sugar and a brief spell of fame.

For the judges, she says, it is about sorting the leaders from those who want to keep it all for themselves. "Always in the first couple of episodes people are jostling for position or putting their marker down, showing all their bravado, and we watch carefully to see how they develop… whether they can work in teams or if it's their way or the highway." The best candidates, she says, "are those who you see nurture other people and give them the right jobs to suit their skills, not the wrong jobs to show them up".

In business as in life, generally speaking women are the more natural nurturers. Counter-intuitively, Brady adds, they tend to be "far less emotional than men about decisions. They make decisions for the right reasons and for the good of them team as opposed to what's next or how does this reflect on me? Therefore, they are better at taking risks."

Brady isn't in favour of quotas for women on boards. "I worry that it is women like me who will get asked to do more non-executive roles than new women coming in… "

"If you don't have a woman on your board you should write to your shareholders and explain why. Tell us how many women you've interviewed and what skills they've been lacking, because that will give us some basis to teach the new generation of women in business."

But she does believe in power lists (she was recently voted one of the UK's most powerful women in a poll for Radio 4). "It helps formulate role models for young women, if you want to be a scientist or a charity worker or a business person, you can start recognising women who have achieved something in that industry.

"We need to do something to push these women into the light."

Home and away: Karen Brady

On football

She said last year of her purchase of Birmingham City FC: "People are amazed when I say this, but I'm no great fan of the game."

On selling her footballing husband when he was a player for Birmingham City

"It didn't affect our relationship. Every time we got a little bit short of cash, he was always one of the assets that got sold off."

On parenthood

"The biggest lesson my kids have taught me is to find the joy in little things, along with a healthy dose of patience."

On Margaret Thatcher's death

"Want something done? Then ask a woman. RIP Margaret Thatcher."

On her brain aneurysm

"The more you read on the internet, the worse it gets – you panic. I was terrified that I would die or have a stroke at any minute."