News earlier this year of merger talks between UK disputes specialists Stewarts Law and Enyo Law took many rivals by surprise.

The proposed tie-up would have created a litigation-only firm with combined revenues of more than £80m. While the talks were ultimately unsuccessful, the mere suggestion of a bigger player in the market has prompted wider debate about litigation boutiques and size – how big is too big?

One such rival, Signature Litigation, has more than doubled its turnover since its launch in 2012, growing from £4.8m for its first financial year in operation to £10.2m for 2015-16.

Founding partner Graham Huntley (pictured) says: "We are building a really strong constitution in a reliable, secure way, which makes it possible for us to grow bigger than traditional boutique firms. What we want is steady annual increases of about 20% or so in revenue, rather than uncontrolled growth."

Co-founder Helen Brannigan – also a former Hogan Lovells partner – left three and a half years ago to become an actress, but the firm has been on a recruitment spree in recent months, and now has 30 fee earners, including 11 partners.

Since September last year, partner headcount has increased by more than half, with new additions including DLA Piper litigation partner Josh Wong, Latham & Watkins London litigation chair Simon Bushell, Bryan Cave litigation partner Ioannis Alexopoulos, and Isolas Lawyers partner Elliott Phillips, who joined to establish a Gibraltar office for the firm.

Previously, Signature had set out a maximum of 15 partners, but the firm is now weighing up the pros and cons of growing beyond that figure.

Huntley explains: "There will come a point at which size might detract from the advantages of our model, but at the same time it has developed very well. We have come to learn more about what growth is possible with the right people and the right structures."

Signature operates a profit-sharing scheme, which gives all of its lawyers and staff a stake in the firm. "We are a cooperative; everyone in the partnership has equity and everyone in the firm has indirect equity. I think there would be a natural resistance to us merging – all the things that are available to us are because we are relatively small, profitable and niche."

In recent years, a spate of litigation boutiques have sprung up in the City, spurred on by the post-crunch disputes boom and the conflicts issues faced by disputes lawyers at larger firms.

They include Cooke Young & Keidan and Humphries Kerstetter, which both launched in 2009; Enyo, which was founded by a team breaking away from Addleshaw Goddard in 2010; Volterra Fietta, established by two ex-Latham partners in 2011; and arbitration boutique Three Crowns, set up by three senior Freshfields Bruckhaus Deringer partners in 2014.

"The litigation market has helped conflict-free boutique firms to grow over the last few years. In the future, you're likely to see this also in other areas, such as in tax and employment," says Huntley.

"The litigation sector has huge advantages in the boutique space, because there is a symbiotic relationship between the growth and bedding down of the international law firms and traction of institutional clients on the one hand, and on the other hand the growth of conflict-free niche firms servicing the jobs those firms cannot do.

"Even if you are not acting for a bank, very often transactional practices are such that you don't want to be to be seen to be acting against the major banks anyway. Markets are like ecosystems; they have parts that work in cooperation with each other – the niche market is working with the top end of the market."

Bushell (pictured right) adds: "I think it is fair to say that the power of the banks in generic terms has diminished over the past decade as they have been clattered by the regulators.

"The follow-on litigation has generated a market for firms that are prepared to sue the banks; and boutique, specialist law firms with a focus on dispute resolution are a perfect home for those kinds of cases.

"This also plays out more widely in the corporate sector. Where the regulators uncover wrongdoing or companies feel they have to self-report the wrongdoing they have discovered, that means civil litigation will follow. Not necessarily immediately, but at some point in the future there will be the need for civil litigation as people will want compensation."

Signature's growth since its 2012 launch has been driven in part by significant referral work from a range of UK and US international firms including Ashurst, Addleshaw Goddard, Herbert Smith Freehills and Steptoe & Johnson.

Bushell says: "Our most valuable friends are big international law firms, as they are the people who generate the most conflict work to refer to us. They'd much rather refer work to a firm that only does litigation and doesn't compete with them on transactional work."

One such recent referral saw Freshfields pass on a dispute between the magic circle firm's longstanding client Ontario Teachers Pension Fund and Macquarie European Infrastructure Fund over interests in Brussels Airport.

According to reports, Macquarie, which owns a 36% stake in the airport, has started looking at selling its investment, and is negotiating with the Canadian investor – which currently owns 39% – over whether it wants to increase its stake.

Signature is acting for Ontario Teachers Pension Fund, with a team led by Bushell and senior associate Nick Storrs, while Taylor Wessing is understood to be advising Macquarie.

Since Bushell joined Signature in January, the firm has also been instructed to advise Ukraine's DTEK Energy. The private coal and power producer is looking to defend its interests in light of the loss of some assets in eastern Ukraine, according to a company statement issued in March.

Bushell comments: "We have been instructed specifically to assist DTEK in defending their interests across a range of complex, cross-border issues." DTEK has lost control of several entities operating in the Donetsk and Luhansk regions since they were declared independent by pro-Russian separatists in 2014.

Other clients Signature acts for include the estate of Arkady 'Badri' Patarkatsishvili, formerly Georgia's richest man; Georgian billionaire Bidzina Ivanishvili; Eurasian Natural Resources Corporation (ENRC); the Royal Bank of Scotland's Shareholders Action Group; and Lycamobile UK.

Signature is currently advising ENRC on a high profile dispute over whether documents prepared for a Serious Fraud Office (SFO) investigation into the mining giant are protected by legal professional privilege. The High Court this week ruled that the documents in question should be handed over to the SFO, but the long-running case is set to rumble on, with ENRC announcing it will appeal the decision.

As for future growth, Huntley says the firm does not have plans to open additional offices, despite its recent launch of a three-lawyer Gibraltar base focusing on trusts work.

"The development of boutiques in London is matched by boutiques in Canada, France and Germany. We can go to whomever we want, whenever we want. Opening multiple offices overseas is not an ambition. Gibraltar is special in that respect."

The extent of growth for boutiques such as Signature remains an open question. "How big is too big for our benefits to remain in place? We don't know. But there will come a point when you will see benefits are being watered down, and then you need to stop growing, at least in the same way.

"There comes a point when the properties of a niche firm are threatened by size, and you have to know what that size is, or you're in danger of taking the firm down the wrong path."