Despite a staggering 30 per cent growth in revenue over the past 12 months in Simpson Thacher & Bartlett's London office, the New York firm only managed 5 per cent growth worldwide in the 2005 financial year, to £399.5m ($727m). It was enough to see it drop one place on last year's rankings.

And yet the firm has been prominent in a succession of major deals under firm chairman Pete Ruegger, strengthening its reputation as a formidable private equity player.

Simpson Thacher's longstanding client Kohlberg Kravis Roberts has been particularly acquisitive this past 12 months. That ensured a steady stream of work for Simpson Thacher, most notably its $22bn (£12bn) acquisition of energy company Kinder Morgan as part of a consortium, one of the largest leveraged buyouts to date. Private equity was also the reason why the London office experienced such growth.

In corporate, the firm has bagged some standout deals, including an instruction from Google on its $1.65bn (£906m) acquisition of YouTube.

Simpson Thacher left international firms with an eye on mainland China in no doubt of its intentions when it raided local firm Fangda Partners for Beijing-based M&A partner Shaolin Luo to establish its operations in the capital. It also snared Shearman & Sterling capital markets partner Leiming Chen for Hong Kong, where it has been since 1993.

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