US firm Dewey Ballantine is ending its alliance with City firm Theodore Goddard to establish its own independent London office.
Managing partner of Dewey Ballantine in London, Brian Morris, said equal numbers of UK and US lawyers would be recruited for the new office.
"We're hoping to expand to 10 to 20 lawyers within six months to a year," he said.
He said the practice would focus on capital markets, mergers and acquisitions and project finance.
"We will not, in the near or probably longer term, be a full service firm," he said.
Morries commented that the plan to establish an office separate from Theodore Goddard should come as "no surprise", because Dewey Ballantine had intended to expand its UK presence from 1991, when it was first represented in London.
"Many US firms are expanding their London offices and I think it is recognition of London's place in the world as a financial centre and our desire to be fully active in this market," he said.
"Our clients have indicated this is a move they welcome."
Dewey Ballantine and Theodore Goddard will continue to maintain their joint offices in Budapest, Prague, Warsaw and Cracow.
Theodore Goddard's senior partner, Stuart May, said the alliance with Dewey Ballantine had achieved an enhanced international presence for both firms.
He said: "The formal relationship in London has now reached the end of its natural life. I am sure we will find many opportunities to continue working together."