Operating profit margins at the U.K.’s largest law firms are continuing to fall despite an increased focus on efficiency, as staff costs rise on the back of weighty associate pay hikes.

An analysis of limited liability partnership (LLP) accounts for the 2016-17 financial year, carried out in conjunction with professional services firm Smith & Williamson, shows that the average profit margin for the U.K. top 50 has dipped by 1 percent every year since 2014-15.