Nick Rucker and Alexandra Ruffel have already quit the firm to establish Berkeley Law, which opened for business last month.
The pair will be joined by fellow LG partners Glenn Hurstfield and Tim Thornton-Jones in May.
The departures leave LG with four partners in its London private client group, which is headed by Anthony Thompson.
Berkeley Law will initially have around 14 lawyers, but Rucker told The Lawyer that the ultimate plan is to operate with around twice that number.
“We do want to grow it but don’t want to get too big,” he said. “We’re a boutique and we don’t want to become a leviathan.
“We want to keep it as a bespoke service for the right kind of people.”