Berlin spy David Smith cost the taxpayer some £820,000 and left his colleagues “angry and betrayed” after passing secrets to Russia, a court has heard.
On Thursday, prosecutor Alison Morgan KC read out a series of statements about the harm the 58-year-old security guard had caused.
The embassy’s head of security Bharat Joshi estimated the cost to the taxpayer of security measures at £820,000.
On the human cost, he said: “The breach of trust, in particular disclosure of people’s personal information, has had a negative impact on staff morale and wellbeing.”
Mr Joshi said: “They had to inform the individuals identified in this material that they must work on the assumption their personal details had been passed on and the staff have had to manage that.
“This had a significant and negative impact on many embassy staff, as described, feelings of anger, betrayal and upset and concern at the implications of their details being shared with a hostile state actor.”
Neil Keeping, from the National Crime Agency, told of the “severe” impact if the details on a whiteboard filmed by Smith had become known.
And he said there were “potentially catastrophic” consequences for disclosure of staff details linked to their “key numbers” and addresses.
He said: “It put at risk each and every UK officer based in Berlin from any kind of attack.
“The consequences of that document being provided were potentially catastrophic.”
An MI5 representative, identified as 2093, put Smith’s spying in the context of relations with Russia at the time.
The officer stated: “At the time the UK was engaged in the calling out of various activity undertaken by Russia including significant concerns at the amassing of military personnel and the activity taking place on the border of Ukraine.”
There was also “concern” among UK authorities at the treatment of Russian opposition leader Alexei Navalny.
There was a “significant impact” and the risks could not “be sensibly described as theoretical”, according to 2093.
Reference was also made to poisoned Russian defector Alexander Litvinenko and the consequences of information being made available to Russian authorities.
Smith, who is originally from Paisley in Scotland, has admitted eight charges under the Official Secrets Act.
The former RAF serviceman will be sentenced at the Old Bailey on Friday.