The U.K.’s largest 50 law firms have made only marginal gains in their revenue per lawyer metric over the last 13 years, lagging both their own revenue growth and the performance of their U.S. counterparts, fresh research has shown.

The data, compiled by International and Legal Compass, shows that the U.K. Top 50 boosted average RPL by just 22.7% since the end of the 2007-08 financial year, despite average revenues for the group having rocketed by 122% over the same period.