Macfarlanes has scooped a new client - and a £1bn deal.
Macfarlanes has been chosen by Compagnie de Saint -Gobain, a French building materials supplier, to handle its bid for UK company Meyer International. The French company usually uses Slaughter and May for its UK legal work.
Slaughters has not missed out on the cross-border deal, however, as it is advising Meyer, which insiders say is also a regular client.
Meyer runs the UK's largest chain of builders' merchants operating under the Jewson and Graham brands.
Sources say it is likely that Slaughters was conflicted out of the matter because both sides on the deal typically use its services. But Macfarlanes is jubilant over being instructed.
Macfarlanes' senior partner Robert Sutton, who led his firm's team, says: "It is our first assignment for Saint-Gobain...it is a significant deal for us. We look forward to establishing a good relationship.
"Saint-Gobain, founded in 1655, is both our oldest and newest client."
Sutton's team comprises Sutton, partner Charles Martin and banking partner Julian Howard.
Corporate partner Simon Phillips at Slaughters is handling Meyer's legal work.
Phillips says the proposed bid was a straightforward cash offer that took 48 hours to push through. Saint-Gobain is now bound to formally submit it before next month.
"Unless a third party makes a counter bid it is very unlikely that the shareholders won't accept it," says Phillips.
Saint-Gobain was unavailable for comment.
Phillips adds that despite working for Saint-Gobain in the past, no conflict arises from Slaughters advising Meyer on this offer because it is a cash bid that is not hostile.
He adds: "If [you were] to say that we are disappointed that is wrong...We barely count Saint-Gobain as a client because it doesn't do that much UK work."
If the merger gets the go-ahead, Saint-Gobain will run the UK's largest chain of builders' merchants.
Investment bank NM Rothschild and Sons and stockbrokers Hoare Govett have been advising Saint-Gobain on financial issues.