Elite UK law firms are losing market share to their US rivals, which have been expanding aggressively in London on the back of US corporate deals, research shows.

The UK’s top 100 law firms saw combined turnover fall to £20.64bn in its 2015 results — a drop of 1 per cent on the £20.82bn reported in the 12-month period ending April 2014 — after some firms were hit by foreign exchange fluctuations including the weak euro.