Justin Stock is the managing partner of Cooley's London office, which opened in January 2015 with 55 lawyers – the largest ever launch by a US firm not arising from a merger.

Stock started out at Werksmans in Johannesburg before moving to Freshfields Bruckhaus Deringer in London. After an eight-year spell with two US firms, he joined Cooley at the London launch and has since grown the office to 80 lawyers. At the British Legal Awards in 2015, Cooley won the London Office of the Year award, with the judges describing the US firm as the "winner by a mile".

Cooley also fares well in several league tables. At 28th position in Fortune's 100 Best Companies to Work For, it has been ranked for three years in a row and is now the number one law firm. Its attraction for young lawyers is reflected partly in the name: the firm has a very cool client base – Google, Facebook, SpaceX and Uber, by way of example. This is underpinned by a strong financial performance. Cooley recorded a 19% increase in revenues for 2014, and 14% in 2015, making it one of the fastest growing firms on the Am Law 100.

Stock remembered this when getting the call from Cooley: "I thought: that's interesting. One of the last big US firms to enter the market; very much in the tech and life sciences space. I went along almost on a reconnaissance mission and met Joe Conroy, our CEO. It was a very good meeting. I quickly saw his vision of what he wanted to build in London and as a European presence, and it very much aligned with mine."

Because a large number of Cooley clients are in Europe, the need to be in London was self-evident: they were sending too much work to other law firms and the tech sector, a core focus for Cooley, was booming in London. But Stock told Conroy: "Please realise it's not like opening in another big US city, where most of the companies would have heard of us – no one in London is going to know who on earth Cooley is." Stock now concedes that he was mistaken: in the UK life sciences space, among others, the Cooley name has significant brand recognition.

Following the meeting, Stock presented Conroy with a business plan for the office, outlining a course for the next five years. "I said it would be great if we could end up having around 35% of the revenue generated by existing firm clients, essentially US office clients, because there's no point just being a silo. But at the same time you don't want to be a service office." Stock got the job – and soon began building the team and the brand in London.

To be able to really understand these fast-moving industries, you have to own those spaces, to truly understand them

Significantly, the office has already reached a figure of roughly 25% of work being generated from US clients. "From my point of view, 25% is a great start; a lot higher than I expected for the first 18 months," says Stock.

Cooley has also added more than 25 lawyers to the office since launch: "We've made great strides and we're not stopping here," he adds. "It is a great challenge making significant numbers of lateral hires, both at the associate and partner level, from different firms with different cultures. Cooley has a special culture of collaboration and support that sets it apart from other firms. We are all focused on maintaining and strengthening it, despite our rapid growth."

In a crowded field of US law firms in London – more than 100 – Cooley has a clear USP. "Something which differentiates us from the many others," explains Stock. It is based on "a really powerful reputation in tech and life sciences for commercial, business-savvy advice".

"To be able to really understand these fast-moving industries, you have to own those spaces, to truly understand them." Stock says that Cooley has a genuine commitment to looking after "not just the companies, but the whole innovation ecosystem". As a USP, he finds that "very exciting". So, it would appear, do the firm's clients.