Jeremy Corbyn rubbed shoulders with the head of MI6 for the first time as Brexit negotiations ignited fears of a snap election, according to reports.
Chief of the Secret Intelligence Service, Alex Younger, reportedly held a meeting with the Labour leader discussing the importance of the agency's work.
The severity of threats facing Britain were made clear, the Telegraph reports, during the detailed briefing on the service's organisational and operational structure.
The "acquaintance" session was held at the MI6 headquarters in Vauxhall, south west London, according to a senior security source.
A Whitehall official, who knew about it, said: "The feeling was that the time had come for Mr Corbyn to become acquainted with the workings of the intelligence establishment."
It comes as Prime Minister Theresa May grapples with Brussels over Britain's Brexit deal, this week sparking fears of a snap election if negotiations fail.
May's stance faced a united Conservative Party attack by pro-EU and arch-Brexiteers in the wake of Jo Johnson's decision to quit as transport minister.
The PM also had to deal with a challenge from Northern Ireland's DUP - she needs their support in order to command a Commons majority.
In the past 24 hours Mr Corbyn has indicated he feels sorry for Mrs May over the EU withdrawal talks, but says she is "following the wrong path".
Asked if he would stop Brexit if he could, the Labour leader said: "We can't stop it.
"The referendum took place. Article 50 has been triggered. What we can do is recognise the reasons why people voted Leave."
He was speaking to German magazine Der Spiegel and insisted if he were in the PM's shoes, he would face the same issues, Mail Online reports.
He said: "No, because we wouldn't be trying to face towards the deregulated economy of the United States, which the one wing of the Tory party is trying to do all the time.
"We would want to make a new and comprehensive customs union with the European Union, one that would obviously protect the Irish border - that's crucial - but also ensure that our supply chains worked in both directions."
He added that "nobody voted to lose their job", for "reduced living standards or working conditions".