The UK's top 50 law firms have grown their partner ranks by almost 6% during the past financial year, fuelled by major merger deals and partnership expansion in the face of an uncertain market.

At the close of the 2011-12 financial year there were more than 9,600 partners across the UK top 50 – a 5.7% rise from last year when partner numbers across the group stood at just above 9,100.

Standout firms for partner growth included DLA Piper, Norton Rose and DWF, which increased partner numbers by 18%, 16% and 19% respectively after mergers, and in Norton Rose's case significant lateral hiring.

Holman Fenwick Willan and Watson Farley & Williams, meanwhile, increased their partner numbers by 16% and 14% respectively following a year of notable lateral recruitment for both firms, including an eight-partner aviation team from legacy Barlow Lyde & Gilbert for Holman and 15 partner hires for Watson Farley.

Equity partner numbers across the group, meanwhile, have seen a slightly smaller percentage rise of 4.4% over the year to pass 5,500, with the increase checked by a handful of restructurings and remuneration overhauls at top 50 firms.

Olswang saw its number of full equity partners fall by one fifth from 55.2 to 43.8 after a partner remuneration overhaul during the financial year, while Nabarro's equity partnership shrank by 15% from 87.5 to 73.9 after 17 partners were cut from the equity.

Leverage – the ratio of lawyers to equity partners –remained broadly static at most firms during the year, with the top 50 average rising from 5.6 to 6.4, in part due to the addition of Parabis to the rankings.

The insurance-focused firm operates a highly leveraged model, with 10 equity partners alongside more than 400 lawyers, equating to a leverage ratio of just less than 40 to 1.

Olswang and Nabarro were also among a number of top 50 firms to see leverage figures increase this year as a result of falling equity numbers, alongside Herbert Smith, for which leverage rose from 7.3 to 8.1 after the firm cut about 12 corporate and finance partners at the close of 2011.

Norton Rose chief executive Peter Martyr (pictured) commented: "I don't think the uncertainty is going to change this year, which means people will be focusing on controlling their cost base.

"Unfortunately, redundancy rounds at law firms have started to become normal again, which isn't good, and we will, as ever, try to avoid wide-scale cuts.

"We have said goodbye to some partners but we have also increased our equity numbers overall," he added.