A man who abused his position as a security guard at the British embassy in Berlin to pass sensitive information to Russia has been jailed for 13 years and two months.

David Smith was arrested in 2021 and charged under the Official Secrets Act for collecting and supplying classified information through 2020 and 2021.

It's believed that Smith, who had worked at the embassy for eight years, had been collecting confidential information for two years prior to the indictment period.

He was found guilty of eight charges involving collecting and passing on sensitive information.

During his trial, prosecutors revealed the highly sensitive information he had collected included government communications labelled "secret" sent by trade minister Liz Truss and another MP to the UK's then-prime minister Boris Johnson.

The court heard he videoed sensitive areas inside the embassy building and recorded classified documents, staff security passes, diplomatic passports and other personal information.

Prosecutors showed the court CCTV footage showing Smith reviewing and filming the embassy's CCTV system from his security booth, saying on one occasion "This'll do, I'll get the rest tomorrow."

During the trial, Smith said he had filmed the documents after drinking "seven pints of beer".

He also admitted to passing information to General Major Sergey Chukhrov, the Russian military attache to Berlin.

Prosecutors said Smith, who had previously spent 12 years working in the Royal Air Force, had fallen prey to extremist conspiracy theories.

They said he had expressed sympathy with Russian authorities, and had hung a poster in his work locker of a cartoon Vladimir Putin with his hands around the neck of former German chancellor Angela Merkel.

Smith accepted the allegation of subscribing to conspiracy theories from the likes of Alex Jones and David Icke, but denied being pro-Russian or having far-right sympathies.

Judge Mark Wall dismissed this and, in sentencing Smith, noted he was motivated by extremist anti-British and pro-Russian views.

"I am sure that you committed these crimes intending to assist Russia, a state which at that time, as now, was regarded as unfriendly to the United Kingdom," Justice Wall said.

Smith argued that he began collecting information during a dispute with colleagues and while suffering from depression "to give the embassy a bit of a slap".

"I can only apologise for any distress I've caused to anyone," he said.

Justice Wall rejected Smith's evidence that he felt remorse as "no more than self-pity".

"I see no logical causal link between depression and a decision to betray your country," Justice Wall said.

Caught in the act

After a second letter to a military attache at the Russian embassy was traced back to Smith in late 2020, MI5 and German authorities formed a plan to catch him red-handed.

In August 2021, Smith was asked by an embassy staff member to escort an MI5 operative posing as a Russian defector, "Dmitry", into the building.

Smith fell into the trap, making records of "highly sensitive information" Dmitry had brought with him, and used his phone to record security footage of Dmitry entering the building.

He later met up with "Irena", another undercover MI5 operative.

Irena told Smith she needed assistance as someone had "passed information to the British and the information could be damaging to Russia".

In hidden-camera footage played to the court, Irina asks if Smith can help and if he will meet her again, and he replies: "I need to speak to someone and then, once that person can then confirm something, I'm willing to meet again."

Justice Wall said Smith "could only have been referring to checking with someone at the Russian embassy to verify that she was genuine" and this was evidence he had an ongoing contact there.

The following day, German police descended on Smith's home in Berlin and arrested him.

He was later extradited to the UK to face trial.

During a raid on his home, German police found devices containing a draft letter to a Russian colonel, in which Smith offered to provide sensitive information as well as the documents he had copied from MI5 agent Dmitry.

They also found images of security equipment, the insides of drawers, whiteboards with staff deployment details and other personal information about employees.

Police found 800 euros ($1,245) in cash in his home and an analysis of bank records showed Smith had not been withdrawing money from his salary.

The court determined Smith had been living off cash Russia had paid him for the information provided.

ABC/Reuters