Deloitte has hired Allen & Overy partner and former managing partner contender Michael Castle to head its legal arm in the U.K., as the Big 4 accountancy firm vies for greater influence in the legal sector.

Castle, who spent 20 years at A&O, will be Deloitte’s first permanent head of legal.

The accountancy had been looking for senior private practice lawyers to lead its legal offering. Previously, the audit firm’s vice chair and partner Mark Tantam had served as interim U.K. legal head, spearheading the search for a permanent leader.

As of late 2017, ALM Intelligence reported Deloitte had 1,800 lawyers, while its legal business was worth $250 million globally.

Deloitte’s U.K. legal team now consists of more than 60 client-facing practicing lawyers and over 125 other fee earners.

Castle joined A&O in 1999 and was elevated to partner in 2007. In 2015, he was one of four partners to vie for managing partner at the firm, losing out to former corporate head Andrew Ballheimer.

“This is an exciting and challenging time for the legal industry. General counsels face a number of converging complexities, ranging from a heightened regulatory environment to an increasingly globalized business landscape, not to mention an acceleration of technological advancements,” Castle said in a statement.

Deloitte said it has big plans to grow its presence in the region under Castle’s leadership.

Matt Ellis, managing partner for tax and legal at Deloitte North West Europe, said, “We have sky-high ambitions for Deloitte Legal in the U.K., and this is why it is excellent to have someone of Michael’s caliber at the helm to build our presence and grow our distinctive suite of legal offerings.

An A&O spokesperson said, “Michael Castle is leaving Allen & Overy. We would like to thank him for the contribution that he has made during his time here and wish him all the best for the future.”

News of Castle’s departure comes on the same day word broke that the head of A&O’s lawyer staffing business, Peerpoint, was leaving the company. It was unclear where Richard Punt, a former Deloitte lawyer before joining A&O, was headed.