By now Linklaters should be more than a little concerned by the seemingly endless onslaught from US firms.

Over the past couple of years, a startling number of highly rated partners from the magic circle firm have migrated to US practices, with this week Richard Hughes and Basil Zotiades joining the list.

There’s been Peter King, M&A partner, who left for Shearman & Sterling, private equity expert David Aknin, who went to Weil Gotshal & Manges, and finance partner Roberto Christofolini moved to Latham & Watkins. Meanwhile, Cleary Gottlieb Steen & Hamilton picked up German-based Dirk Schroeder, a leading antitrust partner, who moved with junior partner Romina Polley.

In fact, Cleary has done very well out of Linklaters after gaining tax partner Nikhil Mehta in 2002 and most recently boosting its London ranks with derivatives and structured products partner Simon Ovenden.

Zotiades’s move makes it a Linklaters double for Latham Paris after taking Christofolini, while the acquisition of Hughes is a first for Sidley Austin Brown & Wood – and what a first.

Hughes is a highly rated lawyer in structured finance, with his expertise spanning, among other areas, securitisation and asset finance.

A natural shoe-in for Sidley’s premier international finance group, Hughes will also be working closely with a former colleague from his Clifford Chance days, John Woodhall, another relatively recent recruit.

Why did he leave? One can only guess, since as usual everyone’s lips are sealed tighter than a Trappist monk’s.

He first joined the firm in 1998 from Herbert Smith. However, Hughes’s sudden move from Linklaters’ structured finance group into the asset finance area 18 months ago seemed a bit odd, especially since he was still involved on major securitisation deals.

Just last week Hughes advised a group of banks on Europe’s first delinked securitisation, executed by credit card giant MBNA and represented by Clifford Chance.

Whatever the cause, it’s yet another loss. Linklaters, for its part, has taken its own fair share of partners from US firms, notably a haul from Shearman’s New York office and Michel Frieh, a private equity expert from Willkie Farr & Gallagher’s Paris base. But in sheer numbers, the US firms seem at this point to be in the lead.

And just when you think that everything has settled down at Linklaters, something else crops up. The firm might want to revisit its policies on partner retention. So far they don’t seem to be working.