The UK's top 100 law firms recorded average fee income growth of almost 7% for the last financial year, according to new research from professional services giant Deloitte.

The results of Deloitte's quarterly law firm survey show the group concluded 2011-12 with a year-on-year Q4 increase of 6.3%, meaning that for the year as a whole, revenues across the group grew by an average of 6.6%.

Deloitte attributed this increase to a 5.6% rise in fee earner headcount among the top 100, while fees per fee earner rose by just 1.1%.

Firms ranked between 26 and 50 were the strongest performers during 2011-12, recording average growth of 9.7%, while international firms mainly saw growth in their overseas ventures, in particular those in emerging markets.

Deloitte professional practices partner Jeremy Black said: "Law firm results have been fairly robust in the current economic environment. But firms are facing bigger issues as they are run under a model which is difficult to sustain with only modest growth. We will see a continued trend for firms to shift their remuneration structures to more merit-based models."

The past week has seen a number of major UK firms announce their 2011-12 results, including Eversheds, which posted a 3% turnover increase alongside a 14% rise in profits per equity partner (PEP), while at SJ Berwin, turnover and PEP both edged up by 1%.

Deloitte's survey also shows the top 100 firms are predicting single-digit growth of around 6% for 2012-13, as the global financial markets remain uncertain.

Bird & Bird chief executive David Kerr (pictured) said: "The increased use of technology and greater regulatory freedom mean pressures on law firms are likely to rise. Only those that can stand out from the crowd are likely to continue to be successful."