The magic circle may have yet to find their dream partners in New York, but the more flexible model used by some London rivals – notably Hogan Lovells and DLA Piper – has allowed them to make considerable progress in the US.

For Hogan Lovells joint chief executive David Harris, formerly managing partner at legacy UK firm Lovells, it has been nearly six years since he realised that a US merger was vital to the firm's future success not just across the Atlantic but globally.

Legacy Lovells had been operating in the US since 1977 and started practising US law in 1995, when it opened an office in Chicago to sit alongside its New York branch. Prior to the Hogan & Hartson merger in May 2010 Lovells had grown its US presence to around 100 lawyers, between them generating 4%-5% of the firm's then £542m revenues.

"Our US strategy had always been to stick to our knitting," recalls Harris (pictured above right). "Build up litigation, insurance, reinsurance, restructuring and intellectual property (IP) but not attempt to build a full service offering. Growing a corporate practice in New York had always seemed to me to be a good way to lose a shed load of money.

"Throughout 2006-07, it became increasingly evident to me that our US strategy had serious limitations both in terms of winning new work opportunities and further expansion. We were seeing a greater demand for a broader range of services than we could do ourselves or would ever be able to build. This tipped the balance to the need to have a full service presence and we realised the only credible way to do this and build a high quality team was a merger," says Harris.

It was a realisation that paved the way for protracted research of the US market and months of discussions with Hogan & Hartson before a vote on the merger in December 2009. The rest is history, with the union creating a top 10 global practice, with around 2,500 lawyers operating across two partnerships under a Swiss Verein structure. The combined firm posted revenues of $1.66bn (£1.05bn) for 2011, of which the US contributed 44%, London 26%, Asia and the Middle East 6%, with the remainder coming from continental Europe.

Since the merger went live the firm has made some 46 lateral hires globally, and drawn up an ambitious international strategy that will see it open in Rio de Janeiro in Brazil in the coming months, with launches in Qatar and Indonesia also planned during the next three years, as well as possible openings in Australia and South Korea.

Meanwhile, in addition to providing greater investment power the union has also improved access to global clients, winning panel appointments including Societe Generale, BNP Paribas, Vodafone and China Development Bank. High profile mandates have included advising ExxonMobil on its US$1.75bn (£1.1bn) sale of North Sea assets to Apache North Sea and on the sale of its Japanese subsidiary to TonenGeneral Sekiyu, a major refinery operator in Japan, for approximately $3.9bn (£2.46bn) and advising SABMiller on deals including its multi-billion dollar takeover bid for Foster's.

Not that the merger has been without its challenges. Partners within the firm suggest there have been considerable cultural tensions – with Hogan's thrusting style at times conflicting with the traditional Lovells' understatement. Both sides have seen senior departures, primarily in Continental Europe. The union will see a major test of the level of partner support later this year, when it moves to fully reflect Hogan's compensation structure.

And the merger has yet to create the large corporate finance practice in the UK and New York that both parties hope to achieve.

Despite the difficulties, to say Harris remains excited about the union would put it mildly. And his reason for the enthusiasm goes beyond the US legal market. He comments: "We wanted to be among a small group of truly global firms and felt that in order to do that you couldn't ignore the biggest legal market in the world. It wasn't just about accessing the US market but about repositioning ourselves as a global player targeting high quality work and our experience since the merger has proved us right."

charlie-geffen-ashurst-newA key question is whether firms like Hogan Lovells and DLA Piper that have used more flexible dual profit centre deals to secure major US/UK unions have the opportunity to leapfrog magic circle rivals, which are committed to expansion either to lateral recruitment or a top-tier merger. And while questions remain over the integration challenges facing DLA Piper – the firm's large US practice is regarded as having been a robust performer in recent years, making ground in key markets like New York and being ready to bid for star partner recruits.

It is also apparent that other major City firms like Norton Rose and Ashurst are increasingly focusing on securing a major US union and see their current run of global expansion as a means to help ultimately deliver a credible deal in the US. In Ashurst's case the firm is hoping its high-stakes tie-up with top-tier Australian firm Blake Dawson, which went live this week, will help the firm build a commanding Asian presence that will be attractive to quality US partners.

Ashurst senior partner Charlie Geffen (pictured) comments: "We see a merger as the only real way to crack the US and think that at some point consolidation will happen as it's the only way to build the mainstream corporate/capital markets practice needed to properly service global clients across London, Hong Kong and the US."