The Balfour family have form in opening gyms. They’ve done it twice, and now are about to do it all over again.

The first venture was Fitness First, started in Bournemouth in 1993 by Mike Balfour. He turned it into the biggest private health club chain in the world and today, the business has some 380 gyms in 16 countries and revenue of £500m.

In 2005 Balfour cut his links when the company was bought by private equity firm BC Partners for £812m but two years later he did it again, starting Jatomi Fitness with his son James.

The company is successful, with 70 clubs around the world, but is pretty much the same as its predecessor. But to hear James tell it, the newer business is unexciting: he describes it as “Fitness Second” and now Balfour junior has a new idea: “I don’t believe in that model anymore,” he says. It is, he adds, typical of a “broken” industry.

So, a year ago, he returned to the UK after spells with the family firm in eastern Europe and Asia, with an idea for a new type of fitness club with a new business model. The plan, devised with co-founder and fellow former Jatomi executive Giles Dean, is for the opposite of the “big box” gym business that his father built, and which still accounts for much of the market today.

Mike Balfour, 65, has signed up as an investor and board member but intends to let his son have free rein. “The two of us working closely on the same business was impossible,” he says, perhaps only half-jokingly. “He learned some lessons along the way, but that’s why he had to do his own thing.”

According to James, 31, there’s plenty of space for a new “disruptive” company in the £4bn UK fitness industry – for a number of reasons. For one thing, he says, the model of the industry-standard 12-month contract, not to mention the joining fee, is solely in the interests of the companies, not their customers.

As a result, he claims, 50% to 60% of UK gymgoers cancel their membership each year. “The average millennial doesn’t want to sign a contract that looks like a mortgage, just to go to a health club.” And, he says, that’s especially true in London, which has a particularly young and itinerant population. “My challenge to Fitness First, Virgin Active and all the others would be: if you believe in your product, tear up your contracts now and see how many people come back. They won’t do it, because they know that so many people will leave.”

A second major reason he believes his new business will work, Balfour says, is that when people sign up to a gym, they effectively pay for access to fitness equipment, when what they really want is to become fitter, thinner or stronger. Personal training is one way to achieve this but, at £50 to £75 per hour, it is neither a particularly flexible nor affordable solution.

So, when his business opens its doors for the first time on Monday, it will offer high-intensity group exercise classes on a pay-per-visit basis, with no contract and no hidden fees.

The first 1Rebel gym – in the shadow of the Gherkin in the City of London – is an 8,000 sq ft space divided into two large studios. One will be for a Spinning-style indoor cycling workout called “Rebel Ride” and another for “Rebel Reshape”, which combines resistance exercises such as weights with intense bursts of running on treadmills. Workouts will be accompanied by pumping music, sometimes from a live band that will join the fitness instructor on stage.

A similar principle has already proved popular in the US, where Barry’s Bootcamp, SoulCycle and Orangetheory Fitness have had success. All three have taken steps to offer their classes to gym-goers in the UK and other countries, but Balfour is keen to stress that 1Rebel sets itself apart from the competition.

He unashamedly admits to being an admirer of taxi app business Uber: “They only take bank details once, there is minimal form-filling, and passengers are emailed receipts for everything they buy.”

So, 1Rebel will offer its customers the same, as well as the opportunity to book classes via an app or the website, and to pick out their exact spot in the class, taking into account the locations of music speakers, fans and the instructor.

This system should have the added benefit of avoiding the “scramble” for prized locations in some SoulCycle classes – “where a place up front is a status symbol, akin to sitting front row at a concert or fashion show” – according to the New York Times.

Another major selling point, according to Balfour, is the quality and size of the changing rooms. A company that fitted out Apple’s Regent Street store was called in to install suspended panes of glass in the showers and customers will be able to take advantage of vintage barber’s chairs, unlimited towels, complimentary cosmetics, GHD hair-straighteners and mobile-phone charging sockets. The interior, according to Balfour, is “pared-back industrial luxe”.

The target audience is mainly women, and those who are cash-rich and time-poor and can afford the cost of a 45-minute session costing £17-£25, according to the number of classes paid for in one go.

It’s not cheap, especially when the new wave of budget gym operators such as Pure Gym – founded in 2009 and now the biggest in the country, with 450,000 members – offer an entire month’s membership for a similar price.

Balfour admits that his contract-free model is not without risk, but points to the fact that it received a ringing endorsement from a crowd-funding campaign that beat its target of £1.15m, raising £1.54m for 34% equity on Crowdcube.

“Initially we wanted to expand very quickly,” Balfour says. “We wanted to have 20 sites across London in three to five years.” But as plans have evolved, it has been decided that it would be wiser to open only five clubs in the same timeframe. “We don’t want to dilute the brand,” he says. “We don’t want the Starbucks effect or, for that matter, the Fitness First effect.”

However, a second site in the City of London is already scheduled to open in April and, if things progress as planned, Balfour sees no reason why 1Rebel could not expand to “other global cities with fashion-forward, fitness-forward people”. He reels off a list that includes the major Scandinavian cities, Dubai, Singapore and Hong Kong, before concluding: “We’ve worked there before, we know people there. So we could do that very, very quickly indeed.”