Lord Sugar and his trusty aids Claude Littner and Baroness Karren Brady are back to appraise a new batch of contestants. As the show marks its 15th series, the trio sit down with Laura Harding to discuss how they keep it relevant.

It seems hard to believe that The Apprentice has been on our screens for 15 years.

Indeed nobody is more surprised than Lord Alan Sugar, who was merely Sir Alan back when it launched in 2005.

"Time has flown very, very quickly," he muses. "It doesn't feel like it at all."

But the series, which pits a bunch of wildly over-confident would-be entrepreneurs against each other in the hopes of dodging the immortal line "You're fired," still rumbles on.

In 2010, the prize changed from a £100,000-a-year job in Lord Sugar's company to a £250,000 investment in the winning candidate's business idea and, according to Lord Sugar, that is how it has lasted so long.

"I don't think I would be have been doing it so long if we hadn't changed it," he admits.

"In fact I know I wouldn't have done it, it was my requisite that we change the format.

"The production company and the BBC get a good product to air but what they do is sign off when the programme is over and then I have to take on the work after that."

And quite a lot of work it has been. Lord Sugar has now invested millions of pounds into the businesses of his winners and the show has adapted over the years to incorporate new technologies and trends.

Indeed the new series will see the hopeful entrepreneurs create a new electric bicycle to pitch to the market, harness new tech to design a rollercoaster for a theme park and venture into the world of music management by marketing an unsigned artist.

Last year's winner was Sian Gabbidon, who triumphed with her idea for a swimwear brand, and is one of a string of female candidates who have done well on the show at a time of increased scrutiny on the number of women in positions of leadership in business.

"I have no preference for women or men," Lord Sugar says. "I just want the best person, sometimes the best is the best bloke and sometimes the best is the best woman, end of story.

"That is always how it's been with me and even before The Apprentice some of the best people I employed were women."

"In the past few years we have had women winners, the last male winner was James (White, who won alongside Sarah Lynn) a joint winner, so what more can we do to encourage, to see that the cream has risen to the top there?"

It remains to be seen how this year's lot will fair.

While the bluster and braggadocio of the contestants is as reliably consistent as ever (one claims "I love business more than sharks love blood"), there is diversity in their background.

One is a para athlete, another a beauty brand owner.

There is also an artisan baker, a librarian and a luxury womenswear consultant, as well as a sports management agent, the owner of an ice cream company and the owner of a pillow company.

That kind of mix should be enough to keep things interesting for Lord Sugar and his trusty advisers Baroness Karren Brady and Claude Littner, who keep an eagle eye on the candidates while they are embarking on their various challenges.

But one fact that is inescapable for the 72-year-old tycoon is he is 15 years older now than when the show started.

"I've often had thoughts of when am I going to give it up," he admits. "Next season will be the 16th."

He stresses that the decision to carry on with the show always lies with the BBC, but adds: "I think I would max out at 20 years, a 20-year ceremony.

"I think enough is enough then, I would be 77 and I might not be compos mentis by then, you never know."

He says the show could carry on without him, but hints it might never be the same.

"One, I've got an exceptionally good memory, and two, I've done all this.

"I started with a little mini van and I've seen anything, done everything, had disappointments.

"I know what selling is all about, know what not to do. I've sat in boardrooms in banks and negotiated big deals with banks at hundreds and hundreds of millions of pounds but (when) I started off, my first sale was most probably five pounds with five car aerials.

"I've loaded lorries, sat on the production line, produced more goods on the production line than any of these people have ever done, done my own marketing, my own advertising, buying components, getting the prices right, designing products.

"I've done it all, so I think they would find it very hard. If you look at some of the other business programmes that are on TV, I'm not sure there is such an all rounder there."

Littner is even more explicit.

"The fact of the matter is Karren and I work very, very hard on the ground but, in all honestly, Alan holds the whole thing together and if you listen hard to the business messages, that is what it's all about.

"So it's very great entertainment but I can't see a situation where if Alan is not involved, that this has got any promise at all."

Baroness Brady nods in agreement.

"They would be incredibly big shoes to fill and I think almost too big.

"If you look at great shows that have changed the lead, they failed and I think this one would go the same way."

With high praise like that was there ever any comparison between him and Donald Trump, who hosted the US version of the show before moving into the White House?

"He was useless, completely useless," Lord Sugar says dismissively. "Totally useless, you cannot even talk in the same breath. There is no comparison."

The Apprentice is on BBC One on Wednesdays at 9pm.