Wilmer Cutler Pickering Hale and Dorr is set to close one of its two London offices as it moves to refocus its UK practice around litigation work at its base in Mayfair.

The decision to move away from transactional work in the UK will lead to the closure of the firm's Alder Castle office in the City as well as its small outpost in Oxford.

It is understood that the US firm's City managing partner Joe Pillman and corporate partner Michael Holter will be among the City partners leaving the firm altogether. 

WilmerHale's Alder Castle office, near St Paul's Cathedral, includes 10 lawyers, five of which are partners.

It was launched in the late 1990s by legacy Boston-based Hale and Dorr, ahead of the firm's merger with Washington firm Wilmer Cutler & Pickering in 2004.

Pillman joined Hale and Dorr in 2000 before its merger with Cutler & Pickering from Oxford firm Morgan Cole – now known as Blake Morgan following a merger with Blake Lapthorn in March 2014 – where he was a partner. He focuses on securities law, including public and private securities offerings and M&A.

Holter joined Hale and Dorr in 1993. He became a corporate partner in 1998 and was managing partner of the London office for two years from 2002 to 2003. His focus is on new media and aviation.

There are two partners in the Oxford branch which opened in 2000, Pillman and employment partner David Andrews. Both work between Oxford and London's Alder Castle.

A spokesperson for the firm said: "The firm is focusing on its litigation practice in London and closing down the transactional practice."

The firm has not yet made the timescale for the closure of the offices public and it is unclear where the departing partners are going.