Herbert Smith is threatening to bar star real estate partner Chris de Pury from joining a rival firm for up to two years, it has emerged, in what would be the toughest exit terms yet publicly imposed on a City lawyer.

The top 10 City firm is in “bitter” exit negotiations with de Pury over his move to Berwin Leighton Paisner (BLP), which is thought to have resulted in de Pury consulting legal counsel.