A former senior Mossad officer appeared in the High Court in London on Tuesday in a dispute between two Russian-Israeli businessmen over African diamonds.

Arkady Gaydamak, who once ran for mayor of Jerusalem, is suing Lev Leviev for around $1 billion which he claims is owed to him in a deal to export diamonds from Angola.

Avi Dagan, who headed a Mossad division before his retirement in 1997, gave evidence on behalf of Mr Gaydamak, as a former business associate who provided advice on security.

Mr Gaydamak argues that he and Mr Leviev signed an agreement to share the profits of diamond sales from Angola but that he stopped receiving payments from 2005.

But Mr Leviev, who has a house in London, denies entering into any such arrangement with Mr Gaydamak.

The case hinges on a paper which Mr Gaydamak says set out their commercial relationship and which they signed at a meeting in December 2001.

According to Mr Gaydamak, the signed document was then entrusted for safekeeping to Chief Rabbi of Russia, Berel Lazar, while an unsigned copy was given to Mr Dagan,

However, Rabbi Lazar lost or destroyed the document, Mr Gaydamak says, while Mr Leviev claims the document related to charitable commitments, not business interests.

In court, Mr Dagan, who was outside the room when the 2001 meeting took place, backed Mr Gaydamak’s version of events, recalling that when the two men came out, they shook hands and said Mazal ubrachah (luck and blessing) - the traditional confirmation of a deal between diamond merchants.

Under cross-examination, Mr Dagan said that he was a “high-ranking” Mossad officer but could not elaborate on his activities “in service to my country”.When asked if he had been involved in espionage, he replied “No comment.”

He gave a similar response when asked if he had been trained in the art of resisting interrogation.

The case, opened last Wednesday and is scheduled to last three weeks.