Aside from testifying to the increasing importance being placed by Slaughter and May on its 'best friends' network, the 'combination' of the UK firm's Paris practice with French ally Bredin Prat is an interesting signpost to both firms' direction.

One source close to Bredin Prat says Slaughters had been mulling over the future of the 40-lawyer office for at least five years. The practice was regarded as having become increasingly out of place as the firm put increasing emphasis on its core 'best friends' network in Western Europe. In addition, the office's heavy UK law finance and tax focus had grown ill-suited to a Paris market that has essentially divided into separate bands of domestically-focused M&A teams and onestop-shop banking advisers.

For Bredin Prat, which has enjoyed success as Slaughters' Paris ally, a finance capability would support its stellar M&A practice in a similar way to its competition, tax and capital markets expertise.

Yet many in the French market question the logic of the tie-up, believing that the French firm needed a fair amount of persuasion from its UK ally, not least because of the problems of digesting such a large team for the 60-lawyer Paris firm.

Certainly the language emanating from Bredin Prat concerning the transfer was a good deal less enthusiastic than the message from Bunhill Row.

Although this can be dismissed as hair-splitting, as the dust settles it emerges that only half of Slaughters' eight Paris-based partners and around 20 lawyers will join the French leader. UK-qualified Paris partner Andrew McClean and some UK assistants will stay at Slaughters, with tax partner Pierre-Pascal Bruneau moving to Debevoise & Plimpton. Commercial and finance partner Antoine-Audoin Maggiar is exploring other options.

The compromise has its attractions, with Slaughters getting rid of its idiosyncratic French practice to focus on the more profitable core corporate finance business, leaving the firm unambiguously positioned as a UK-law driven practice.

And, by not taking the whole office, Bredin Prat has a more digestible option for a finance team.

Even so, it is a major shift for Bredin Prat. With Rambaud Martel this month being swallowed by Orrick Herrington & Sutcliffe, arguably Darrois Villey Maillot Brochier is left as the only real M&A boutique among Paris' legal elite.

Much attention will now focus on whether Bredin Prat has the will to build on its new banking additions in a market where, aside from Gide Loyrette Nouel, finance has been left to foreign firms. Others may question the wisdom of moving away from the boutique model that has proved so resilient to the advance of UK firms.

Whatever the underlying reasons for Slaughters' and Bredin Prat's dramatic development, a deal is sealed and so is the close relationship; best friends do not always agree and, once in a while, sacrifices have to be made in order to help each other out in tricky situations.