He's a liar. A baraggart. A probable narcisist. Previous colleagues have said this repeatedly. MI6 and MI5 also know.
As long as the meeting was not in the Russian Embassy any Russians attending would at the very least be concerned it was bieng monitored in some way or other. Even if monitoring him by name might be politically they can quickly target those who might contact him. Because the Secret Service isn't going to trust someone who would have been flagged as a security risk from personality alone in his early 20s by someone with an A level in Psychology.
Hes not singlehandedly the Cambridge Spy ring.
Of the litany of things he's done this really doesn't matter.

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