David Ballantyne Smith, 58, pleaded guilty to eight charges under the Official Secrets Act 1911 and 1920 but claimed he did not intentionally cause any harm.

He was sentenced to 13 years and two months but can serve the term in either Germany or the UK.

Smith, from Paisley, Scotland, claimed he was depressed, lonely and drinking up to seven pints a day when he started leaking embassy secrets in an effort to cause embarrassment.

Mr Justice Wall dismissed this during sentencing at the Old Bailey, saying he collected "a significant amount of material" to "damage British interests" and provided that information to a "hostile power".

"It was your job to ensure the embassy was secure and its staff safe. It was the most obvious breach of the trust placed in you," the judge said during the televised sentencing.

He said Smith's "persistent, and to an extent, sophisticated" information gathering had caused "understandable anxiety and stress" to the embassy's staff and their families.

The judge said Smith was "paid by Russia for [his] treachery" but there was no evidence the payment amounted to "life-changing sums of money".

Smith took photographs and documents from desks and drawers, as well as filming CCTV footage.

He provided names, photographs and personal details of embassy staff to Russian officials, as well as secret documents including correspondence to then prime minister Boris Johnson.

He also filmed an extensive walk around the embassy which revealed the layout of the building and its offices, taking care to film through windows.

Smith's spying could have harmed Britain's international trade negotiations and came at a time the UK was "calling out" Russian actions, including amassing vast numbers of troops on the Ukraine border, the judge said.

Mr Justice Wall also provided details about the sting operation that led to Smith's arrest.

A British agent visited the embassy posing as a Russian defector named Dmitry. He offered to pass sensitive information to British authorities in front of Smith.

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During the visit, Smith was told to copy what he believed was a secret Russian document and destroy packaging from a SIM card with the defector's phone number on it. Smith fell for the ruse and an extra copy of the document as well as the SIM packaging was found in his home.

The cost so far of securing the British embassy in Berlin after Smith's crimes stands at £820,000.

Mr Justice Wall said Smith "developed decidedly anti-British and anti-Western feeling" and that this was the "direct cause" of the offending.

Colleagues heard Smith criticise the UK and Germany and felt he was sympathetic to Russia and President Putin.

He admitted to openly supporting Russian-backed forces in the Donbas region of Ukraine.

While Smith's sentence relates to crimes committed from 2020 to his arrest in 2021, the judge said he was sure the former security guard began collecting information in 2018.

Home secretary Suella Braverman said Smith's sentencing was a "great result for British justice".

"He betrayed our country and it's credit to the brilliant work of MI5, our police, and their cooperation with German authorities that he's now been sentenced to 13+ years in jail."

In a Twitter post, security minister Tom Tugendhat called Smith "a traitor".

"He betrayed us all and put our embassy and our country at risk. I'm grateful to MI5 and their amazing officers, the police and our German partners for seeing him put on trial and sentenced," he said.