International diamond broker Willie Nagel is suing jeweller Laurence Graff and his company Graff Diamonds for more than £15,000 over an alleged breach of contract.

Mr Nagel, chairman of W Nagel Limited, had been broker to Mr Graff, 69, for 30 years. In 1998, as part of his services, he secured coveted "sightholder" status for Mr Graff. Sightholders are privileged traders, granted access to viewings of diamonds for inspection.

According to a High Court writ seen by the JC, Mr Nagel was told in 2004 that Graff Diamonds was forming a new company to apply to be a sightholder in London, and that a new broker had been appointed. Graff had been considering forming such a company, the writ says, since 1997, and Mr Nagel was aware of these intentions.

The writ claims Mr Graff acted in breach of a 1999 agreement made with Mr Nagel. No hearing date has been set.