The leader of the United Kingdom's Labour Party, Jeremy Corbyn, has called for an inquiry into the activities of an Israeli embassy officer who was caught on tape in an Al Jazeera investigation discussing a plot to "take down" British politicians.

In an open letter to Prime Minister Theresa May, Corbyn described the actions of Israeli embassy official Shai Masot as "improper interference in this country's democratic process".

Explaining that he was "concerned" by UK foreign minister Boris Johnson's announcement that the embassy's activities were a closed matter, Corbyn urged May to launch an inquiry: "This is clearly a national security issue."

He continued: "It is only on [the basis of an investigation] that Parliament and the public will be reassured that such activities will not be tolerated by your government."

Masot was forced to resign from his position earlier this week, and Israeli officials have claimed he was a lone actor who was acting without the guidance or permission of his superiors.

The investigation, The Lobby, reveals plots by the Israeli diplomat and a British civil servant to destroy the careers of senior politicians.

Supporters of Corbyn, who is a leftist with a long history of Palestinian solidarity activism, were among those accused of anti-Semitism by Israeli officials, as Al Jazeera's six-month investigation documented.

In The Lobby, Al Jazeera Investigations exposes how the Israel lobby influences British politics. Among the revelations were Israeli attempts to smear activists who question the illegal occupation of Palestinian land by helping to build racism cases against them.

Al Jazeera Investigative Unit's series "The Lobby" can be viewed on Al Jazeera:

Episode One: Young Friends of Israel - Available online

Episode Two: The Training Session - Available online

Episode Three: The Anti-Semitic Trope - Available online

Episode Four: The Takedown - Saturday, January 14, 22:30 GMT