The City's mid-market challengers are breaking into the premier league of the UK's legal services market after outperforming their larger London rivals.

The mid-tier posted an average equity partner profit increase of 22.4% to take its average partner profits figure to £549,000, just below the chasing pack's figure of £554,000. The rise surpassed the top 50 average increase of 19% and rose significantly from the mid-tier's corresponding figure for last year of 16%.

Eight of the 13 mid-tier firms now have higher average partner profits figures than the majority of the chasing pack firms and are increasingly colonising areas of the market once the preserve of firms like Ashurst and Lovells.

Notable increases came from Stephenson Harwood and Taylor Wessing, which both achieved partner profits rises of more than 40%. SJ Berwin, Olswang, Bird & Bird, Travers Smith, Field Fisher Waterhouse and Charles Russell all saw rises of more than 20%.

The mid-market firms also recorded above-average increases in revenue of 16%, compared with an 11% rise last year.

SJ Berwin's 27% rise in turnover singled it out as the fastest growing mid-tier firm and the second fastest growing top 50 firm.

The average leverage in the mid-tier rose slightly to 5.15 lawyers to each equity partner, up from 5:1 last year but is still significantly lower than the top 50 average of 6.3.