Deloitte has hired Allen & Overy (A&O) partner and former managing partner contender Michael Castle to head its legal arm in the UK, as the Big Four 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 accountant had been looking for senior private practice lawyers to lead its legal offering, as it sought to build its sector presence.

Previously, the audit firm vice-chair and partner Mark Tantam had served as interim UK legal head, spearheading the search for a permanent head.

As of early last year, Legal Week parent company ALM's intelligence arm found the firm had 1,800 lawyers, while its legal business was worth $250m globally.

The Deloitte Legal UK team now employs more than 60 client-facing practising lawyers and more than 125 other fee-earners.

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

Castle said: "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 globalised business landscape, not to mention an acceleration of technological advancements."

Matt Ellis, managing partner for tax and legal at Deloitte northwest Europe, said: "We have sky-high ambitions for Deloitte Legal in the UK, and this is why it is excellent to have someone of Michael's calibre 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."