Freshfields, Allen & Overy and Eversheds will lose a FTSE 100 client if the board of Anglo-US automotive and aerospace company LucasVarity gets the go-ahead from shareholders to move the company's headquarters to the US.
LucasVarity is keen to relist in New York to tap into what it sees as a greater institutional investment interest in the automotive and aerospace sectors.
It also plans to execute a 20 per cent share repurchase programme, limited to 3 to 4 per cent a year under UK accounting and tax restraints.
New York-based firm Cahill Gordon & Reindel is US counsel to the company and is expected to pick up most of the new US-based instruction.
In the UK, LucasVarity receives debt advice from Allen & Overy and its corporate work is done by Freshfields and Eversheds. The company will maintain a secondary listing in London.
Julian Francis, lead partner for LucasVarity at Freshfields, said the firm would continue to act for LucasVarity in Europe and the Far East.
He said Cahill Gordon & Reindel lacked a significant presence outside the US.
"We will probably lose some yellow book work, especially if the company makes acquisitions in the States that Cahills can handle. But if it is outside the US, we hope they will come to us."
LucasVarity's shareholders will cast their votes on the move at the company's extraordinary general meeting on 6 November.
But if the company does relist in New York it is unlikely to mark the start of a mass exodus from London's capital markets.
Hugh Nineham, Lovell White Durrant's head of corporate, said that corporate interest in a London-listing was still extremely buoyant.
Lovells has several overseas clients which plan to relist in London over the coming months. "They simply want access to the wider markets that a London listing will allow," said Nineham.