SJ Berwin & Co, Olswang and Bird & Bird have joined Freshfields and Clifford Chance in increasing their income by more than 30% for this financial year.
In the latest performance figures obtained by Legal Week, Olswang laid claim to being the UK's fastest-growing firm with a 48% rise in income (see front page story).
Rival Bird & Bird saw its turnover shoot up by 33% in a year when the firm held lengthy but ultimately aborted merger talks with US firm Orrick Herrington & Sutcliffe.
The firm has also invested significantly in its offices in Paris and Brussels. A spokeswoman said the Paris office which opened in January, had been "going great guns".
Under the helm of former Jeantet & Associes telecoms partner Frederique Dupuis-Toubol, the office already has nearly 30 lawyers.
Bird & Bird's Brussels practice has also enjoyed rapid growth, up from three lawyers to 40 in the last 18 months.
SJ Berwin, the firm that, along with Clifford Chance, was at the forefront of the recent salary war, was another firm to post an fee income rise in excess of 30%. The firm's results were driven by a strong performance from its corporate department.
Mid-sized firms across the board have benefited from the strong economy and corporate boom, with firms that are focused on areas such as media, telecoms, technology and e-commerce doing particularly well.
Both Theodore Goddard and Richards Butler successfully shrugged off the distraction of their failed merger talks, which collapsed at the beginning of 1999, to report healthy rises in turnover.
Theodore Goddard managing partner Peter Cooke said all practice areas performed to budget, with corporate and corporate finance "well in excess".
Although figures for Richards Butler's worldwide income were unavailable as Legal Week went to press, the firm saw turnover at its London office rise 14.3% to £40m.
Elsewhere, Charles Russell managing partner Grant Howell, reporting a 13.6% rise in income to £30m, said: "It has been all-round quite strong." In particular, Howell praised the firm's media/ communications and employment departments.