Hogan & Hartson is to lose the head of its City corporate team, Jonathan Coppin, after less than 18 months with the US law firm.

Coppin, who joined Hogan last summer from the London arm of US rival Shearman & Sterling, told partners of his decision to leave the firm – and the law – last month.

Meanwhile, part-time employment specialist Nicola Walker – the firm's only employment partner in the City – has retired from private practice to focus on her work with a London employment tribunal.

The loss of Coppin – who is understood to be taking some time out to consider his next move – will be seen as a blow to the US firm, which had planned to develop its English-law corporate team under the leadership of the former Shearman and Norton Rose partner.

Office head Garry Pegg and dual-qualified corporate partner Daniel Maccoby will oversee the City transactional practice until a permanent successor at the helm of the practice is confirmed, with Coppin – who will retire from the partnership at the end of 2007 – helping with recruitment efforts.

Coppin is expected to continue working at Hogan until his current deal – advising Ford on its high-profile disposal of luxury car brands Jaguar and Land Rover – closes in early 2008.

Other headline deals on which Coppin has advised since joining Hogan include acting for Russia's Norilsk Nickel on its $4.8bn (£2.42bn) bid for Canada's LionOre Mining.

Pegg told Legal Week: "Jonathan is a great guy and has made a terrific impact here. He is going to [leave] a big pair of shoes to fill. Over the last 18 months we've turned a massive corner in London and while we don't like to lose good people, we have an institutional base here that's going places."

One partner at a rival firm added: "He is obviously a loss to the City and I would imagine he'll be a loss to Hogan."