RichardsButlerhas entered merger talks with New York firm Proskauer Rose after several years of looking for a US tie-up.
The City firm has made transatlantic capability a strategic priority as part of its repositioning as a disputes specialist.
Proskauer, which is also a specialist litigation practice, is one of the few major New York firms without a presence in the UK, having closed its small London office in the early 1980s.
Weve looked at London for the last five years, admitted Proskauer chairman Alan Jaffe, adding that the firm had talked to a number of UK candidates about the possibility of a merger.
One source close to the talks said Proskauer partners now feel their firm needs more credibility internationally.
Proskauer was ranked 58th in The Lawyer Global 100, with gross revenues of 223.4m in 2003. A merger between the two firms would create a transatlantic firm with around 1,000 lawyers and with revenues of more than 300m.
Around 55 per cent of the New York firms work is litigation and approximately 45 per cent transactional a split which almost exactly mirrors Richards Butlers 53 per cent litigation, 47 per cent corporate.
The two firms also have similar revenues per partner of 1.58m at Richards Butler and 1.45m at Proskauer, but the US firms high profitability could prove a stumbling block.
Richards Butler managing partner Roger Parker declined to comment on the talks, stating only that were not in negotiations.