Six of the top 10 UK law firms are large enough to be included in the FTSE100 index of blue chip companies if they were stock-exchange listed, according to a new study.

Corporate advisory firm Europa Partners said value-per-equity partner in the biggest four firms now averages £6.8m. Allen & Overy is the largest UK firm with an estimated value of £2.6bn. Freshfields, Linklaters, Clifford Chance, Hogan Lovells and DLA Piper are all valued at more than £2bn.

Europa’s second annual study of leading UK firms showed consistency in valuation. The top 10 firms, which also take in Slaughter and May, Herbert Smith, Ashurst and Eversheds, are the same as in 2011 and their absolute values are generally little changed.

Below the top 10, the market is much smaller and more fragmented, with 20 firms boasting values of between £100m and £400m.

Robert Colthorpe, a partner at Europa, said: ‘This looks increasingly like a period of great change and opportunity for UK law firms. You are seeing leading firms becoming more sophisticated and strategic in the ways they are seeking to quantify business value.’

The study concludes that UK firms are well placed to grow and extend their competitive advantages, with many looking at raising capital to facilitate international expansion. Hogan Lovells today confirmed it will open an office in Rio de Janeiro, becoming the first full-service international law firm to operate in the Brazilian city.

The Brazil market has traditionally been difficult to access but Rio is an attractive proposition for large-scale project and real estate work, with the city hosting the 2016 Olympics and key matches in the 2014 football World Cup.