The UK's 100 biggest law firms by revenue have witnessed their slowest growth in seven consecutive quarters, but still managed to grow their billings by 3.4%.

Deloitte's latest Quarterly Legal Sector Survey for the period ended 31 October 2012, revealed it was the fourth consecutive quarter where growth has slowed, compared to 10% in the same period the year before.

The top 10 firms witnessed a relatively flat performance, recording growth of less than 1%, while those in the mid-tier were buoyed by merger activity that helped drive a 5.8% increase in revenue.

Jeremy Black, partner at Deloitte's professional services practice, said: 'We continue to see suppressed growth rates in the legal market. Whilst the mid-tier firms appear to be enjoying slightly stronger growth, this is predominantly due to increased merger and acquisition activity.

'The change in attitude towards merging with bigger competitors only serves to highlight the 'survival of the fittest' reality that faces elements of the professional services sector. Previously, most firms favoured amalgamating with a smaller peer, retaining management control and their name. However, as clients seek value for money and law firms adopt cost saving measures, merger opportunities continue to become more attractive.'

The report intimated that a tough, competitive domestic market, is forcing change in the mid-tier firms' profile.

'Consolidation is one way to expand the client base and also deepen specialist knowledge - whether that is in an industry focus or a practice area,' Black said.

The Big Four firm revealed that 71% of professional services firms have been in merger or acquisition talks in the past 12 months. In 2011, 81% of those involved in merger discussions wanted to join with a smaller firm. That figure has plummeted to 52%, this year, with 24% wanting to embrace businesses of a similar size while another 24% seek opportunities with larger firms.

Black continued: 'The change in attitude towards merging with bigger competitors only serves to highlight the 'survival of the fittest' reality that faces elements of the professional services sector. Previously, most firms favoured amalgamating with a smaller peer, retaining management control and their name. However, as clients seek value for money and law firms adopt cost saving measures, merger opportunities continue to become more attractive.'