The one-stop shop, the global law firm, globalisation – the radical and much-documented changes to the legal services market that have gripped the profession for the best part of two decades have operated under many guises.

Another model, formed as much by such trends, is the 'best friends' network of independent firms, a model that Slaughter and May has arguably elevated to an article of faith for those who oppose the corpora-tisation of law.

It is nearly 10 years since the firm, shaking off decades of tradition forged by its status as London's top corporate adviser, began actively marketing its close links with foreign law firms as a model that could compete with the one-stop shoppers.

Though the tag 'best friends' was coined by outside commentators, the concept of selling the firm's already highly-developed referral network to the wider market represented an audacious attempt to reposition a City legend for the modern age.

In particular, then senior partner Giles Henderson was intensely concerned that a perception of Slaughters as a little Englander would have a poisonous effect on the firm's ability to attract the best trainees.

The intervening nine years have unsurprisingly proved more complex than the punditry of the time suggested, with the international firms facing a downturn in their core M&A businesses between 2001 and 2004, mid-way through painful post-expansion integration. At the time, the more flexible strategy of Slaughters started to look the better bet.

But with Europe's deal markets well into recovery mode, fresh questions will inevitably be asked of Slaughters' approach and, by extension, the entire network concept.

There is no question that Slaughters remains as wedded as ever to its network, which reads like a Who's Who of the leading independent law firms in Europe.

In France, profitable M&A boutique Bredin Prat tops the directories for deal lawyers and routinely surfaces on the market's largest bids. Elite German firm Hengeler Mueller is also widely regarded as the most successful corporate practice in its home jurisdiction and last year further expanded its domestic coverage with a launch in the much-touted Munich market. Similar plaudits are forthcoming for Madrid's Uria Menendez and Italian practice Bonelli Erede Pappalardo.

Each jurisdiction covered by the network is over-seen by a partner, with senior figures such as David Johnson, Mark Bennett and George Goulding among those with European briefs at Slaughters.

The firms also frequently co-operate on joint pitches and will submit single or combined bills, largely to the requirements of clients.

"Everyone recognises our model as unique. But it is very successful and others envy it," contends Hengeler corporate partner Oleg de Lousanoff. "On an operational level, we have achieved a degree of integration similar to a one-stop shop, but have kept the administration apart."

Uria co-managing partner Jose Maria Segovia adds: "For international transactions, especially M&A and financial transactions, we are able to provide a high-quality service to investors, wherever they come from.

We can provide the same services in the same places as a global firm but with an extra quality that is very difficult to get in global firms."

For independent firms on the Continent, many of which have witnessed at close hand the ruinous effects of failed international mergers, the appeal of the model is obvious.

Members of the network can wield considerable international clout without being subsumed into a major international practice, meaning that the independence much prized on the Continent is preserved.

Indeed, for all the talk of best friends and the drift towards exclusivity that status implies, members speak with one voice of the need to maintain a degree of separation.

"The important thing to remember is that while we are associated with a number of firms, none of those relationships are exclusive," says Slaughters practice partner David Frank. "We just work a lot together."

Segovia adds: "We are delighted to have 'best friends' provided it is not understood as a closed circle."

The network currently has at least 15 inter-firm working groups, organised largely along practice lines, looking at matters of common interest, with an overall steering committee responsible for determining the direction of the network as a whole.

Although issues such as common branding do regularly come under review, observers looking for signs of accelerated integration should not hold their breath.

That process has been a slow one, according to Segovia. He comments: "Uria always had the position of wanting to remain as an independent firm in the Iberian market. Having said that, in a natural way we are starting to have deeper relations with similar firms in other countries.

"We are happy with where we are," he adds. "When we are working together on a particular project, that must be publicised, as many of our clients may not be aware that we have acted on a pan-European deal for other clients. Maybe joint visits to clients could be done… but [there will be] nothing like a common brand or even bigger ties. We have got to be extremely careful about taking more steps in the direction of getting closer."

De Lousanoff agrees that a more concerted marketing effort could be beneficial, pointing to the high aggregate deal rankings achieved by the combination of German leader Gleiss Lutz, Benelux practice Stibbe and Herbert Smith.

He suggests that similar treatment would see the best friends sat atop the deal rankings, though the joint ranking of Herbert Smith's alliance relies on an integrated conflicts system, which Slaughters' alliance has always baulked at.

Indeed, partners across the Slaughters network cite the huge potential for conflicts as a key factor that makes substantial integration between its own member firms unlikely. Meanwhile, the network itself must expand to take account of emerging markets further afield.

"The network is a process of constant development," says Frank. "We will develop where our clients require.

The overall objective is to create a virtual law firm that can deal with any transaction."

Accordingly, the firm has turned its focus to new European Union (EU) accession states and other areas of Eastern Europe, as well as the major emerging centres of India, Russia and China.

Last year it emerged that the firm had targeted a handful of leading local firms in Poland, Romania and the Czech Republic as part of a concerted push to bolster its links in the Central and Eastern Europe (CEE) region, which saw a major upturn in M&A activity in 2005.

Firms targeted included leading Polish firms Soltysinski Kawecki & Szlezak and Wardynski & Partners, Bucharest-based practice Nestor Nestor Diculescu Kingston Petersen and Czech firms Prochazka Randl Kubr and Glatzova & Co.

Advisers in Hungary, Bulgaria and Slovakia were also approached, while Russia – where Frank concedes that awareness of the Slaughters brand is "patchy" – is currently high on the agenda.

"It has always been the plan to develop links in the jurisdictions where our clients are doing business," he says. "In most countries we are not starting from a blank piece of paper, but have longstanding links that we are trying to build on and develop. Russia is one example where we comparatively recently started from scratch."

Last November, meanwhile, the Slaughters network sent a delegation of senior lawyers to China in a bid to bolster its links with local firms in the region.

Network representatives met counterparts from leading Chinese firms King & Wood, Jun He and Haiwen & Partners, which have acted as informal referral partners since Slaughters opted in 2004 not to launch an office of its own in the mainland.

The Chinese issue raises a particular dilemma for Slaughters, given the country's rapid development as a major economic power and the world's most coveted emerging legal market. The speed with which such a strategically-important market could open obviously plays to the strengths of global giants, who can hire aggressively to move into new markets.

Although another senior delegation from the network – the third to date – will head for China in July, Segovia suggests that the country is not currently a top priority for Uria.

In contrast, Slaughters this month hired Morgan Stanley in-house counsel Lisa Chung to boost its Hong Kong office, underlining its commitment to the wider region.

If China presents particular challenges to the network, the other market that many believe will ultimately decide the success or failure of the grouping is North America.

Understandably, Slaughters and co have been eager over the last decade to make the most of their referral advantage at a time when the firm's magic circle rivals are either attempting to move into US law or hunting, however wearily, for a US merger.

Corporate chief Chris Saul and M&A head Stephen Cooke are among those with responsibility for developing the network in the US, where Davis Polk & Wardwell heads a group of referral partners that also includes Manhattan royalty Cravath Swaine & Moore and Wachtell Lipton Rosen & Katz.

Frank says the firm has experienced a "discernible upswing" in the number of referrals it receives from the world's largest legal market since many of its London rivals declared their US law ambitions.

"We are clearly more aligned with the US model than some of our competitors," observes Frank, "[and] there is no way we can be seen as competition."

Parallels are inevitably drawn between Slaughters and the compact, ultra-profitable models of Wachtell and Cravath – firms comfortable with their strict focus on domestic law and hitherto unburdened by strategic uncertainty.

Potentially more problematic are the international ambitions of other associated New York leaders, with another referral partner, Sullivan & Cromwell, ominously turning its attentions to European law.

Sullivan has already secured a chunk of the Paris deal market, fielding highly-respected M&A partners such as Gerard Mazet and Dominique Bompoint, while the firm this month launched its own long-awaited UK corporate capability with the hire of Allen & Overy partner Vanessa Blackmore.

Last summer Davis Polk also signalled its own European push with the hire of Freshfields Bruckhaus Deringer partner and French co-head of M&A Arnaud Peres, marking its foreign law debut. Although Davis Polk reaffirmed its commitment to the Slaughters network, maintaining the push was specific to France, that will be of little comfort to Bredin Prat partners.

Elsewhere, another Slaughters regular, Simpson Thacher & Bartlett, has continued to move into local law in Europe, primarily in acquisition finance.

And while the best friends network has certainly widened its appeal to US firms, a danger remains that inter-firm links become weakened as referrals are spread more widely.

"Most of the firms [with London offices] that we have relationships with are not practising English law, so in a way it is complementary," says Frank. "Some firms, such as Bonelli, do have English law lawyers over here, but we do not see them as a threat as they operate in largely different [practice] areas."

The issue took centre stage last December when Slaughters tellingly offloaded its 40-lawyer Paris branch, which practised both English and domestic law, to Bredin Prat.

"That is evidence of the increasing closeness between the two firms and the synergy between the two offices," argues Frank, countering persistent claims that the office may have been a source of tension between the firms.

That decision followed the closure in 2004 of small offices in Singapore and New York.

"Five years ago, people were talking about the global model," concludes Frank. "Now people are more receptive to our own model. But there is no single 'right' answer to how to address the international question. Had we decided many years ago to develop our capabilities abroad we would be a very different outfit from what we are today."

So what is the future for Slaughters' network? While it is acknowledged that the flexible grouping of firms has proved more resilient than many predicted, it is clear the model faces serious challenges ahead. The acid test will surely be whether the grouping can hold its market share of premium M&A and securities work in its European heartlands.

Here, the omens are mixed. For example, Mergermarket's M&A rankings for the last boom year of 2000 show Slaughters ranked third in value , just behind traditional rivals Linklaters and Freshfields, both much larger firms, while Hengeler was ranked seventh.

By 2005, Slaughters' ranking had fallen to 12th, while Hengeler was down in 22nd place. Even if individual rankings can be dismissed as volatile indicators, Slaughters cannot, in the long term, afford to be seen to slip too far down the rankings at a time when continental M&A is taking off.

Likewise, the firm will soon have to contend with the realities of competing with post-integration global giants. Slaughters has, after all, had well over 100 years to craft its model, while the global firms are still in their infancy. The integration and service of the newly-formed international firms may have been initially patchy, but there are already signs that the offering has improved markedly. A related issue is the undoubted inroads made in markets such as France and Spain by international firms, in particular US firms, whose more individualistic partner-ship culture has in many ways made them a more deadly threat to Slaughters' continental allies than the London magic circle.

So far, the feeling is that if any group of firms can successfully pursue independence, and make the network model work, these are the firms that will succeed. But the real test is yet to come.