In the heart of Camden's bustling stalls and food markets sits the Atrium, an uber-modern office space packed with entrepreneurs, startups and creatives. Among them is TandonHildebrand, a new-model firm founded by two City partners disenchanted with billable hours, timesheets and old-fashioned attitudes to working.

The four-lawyer corporate and employment specialist spun off from Trowers & Hamlins in April after what co-founder Tania Tandon described as a growing "inequity" inherent in the traditional legal services model, particularly with regards to time-recording.

"At the start of our career, my peers and I all felt that the value placed on time-recording was strange," says Tandon. "The more senior I got, the more the inequity of this bothered me. I discovered more and more that I didn't like. I never thought then that this model would remain unchanged for over 20 years."     

Tandon and co-founder Richard Hildebrand worked together for more than 13 years at Trowers, where Tandon led the international employment team and Hildebrand was a senior corporate partner, and the duo were also drawn together by a shared unease with the traditional partnership model.

"We formed a vision of what our ideal law firm should look like and came to the realisation that it was different from firms we knew, including the one we were partners in," says Hildebrand, who with Tandon shares an ambition to "eradicate chargeable hours and timesheets and adopt a new staffing model based on mutual trust and confidence".

Labels like 'agile working' or 'flexible working' can be used to stigmatise working mothers

The launch marks the latest example of partners breaking away from established practices to go it alone, following the launch of Himsworth Scott by former Schillings duo Chris Scott and Matt Himsworth, while James Dakin and Karen Mason recently broke away from Boodle Hatfield to found New Manor, finding that "innovation in legal services was long overdue".

"The traditional model can carry with it an incentive to take longer to do something," says Hildebrand. "How can this be in the client's interest? The client wants cost certainty, to know that the work will be carried out efficiently and with the client's best interest at heart.

"Our model is about the right person, at the right level, with the right skills delivering to the client in the most efficient way. This would all be negated by the pressure to record time."

The two believe what also sets them apart is their three-pronged fee structure, which gives clients flexibility and delivers "what clients want", while "doing away with the infrastructure of the traditional model". As well as the fixed fee, the firm also operates a 'risk sharing' model – where a portion of their fee is based on a particular outcome – and a further model whereby the fee is determined by the client, with a view to establishing lasting relationships.

"Rather than selling our time we are selling our value, experience and expertise to our clients," says Hildebrand. "A fixed fee is set, the advisers can relax and get on with the advice without worrying about how long it takes.

Tandon adds: "The idea of having policies, procedures and prescriptive hours means you're not building mutual trust as adults. We don't prescribe holidays or hours, and we don't believe in appraisals. We don't think this is how to get the best out of people. And they don't abuse this – they want to deliver a good service. Constraining people is unhealthy."

But for Tandon in particular, the decision to break away is about more than just a weariness with entrenched ideas around fees and time. She claims concepts like flexible working – still novel among City firms – while welcome, present challenges to working mothers like her.

"I've felt uncomfortable with labels like 'agile working' or 'flexible working' for a long time, in part because I feel it can be used to stigmatise working mothers," she says.

"You'll hear people say, 'oh, is she one of those flexible working people', or 'let's not give her the work, she's one of those part-timers'. It breeds mistrust. The intention behind these terms is good but they are not the solution. For us, you can come and go as you like, no need for permission or a discussion. Lawyers are motivated to get the job done.

"And I hope that when my daughter is old enough to work, there won't be a category for 'working mums'. After all, nobody says: 'He's a working dad.'"