The two suspects, who are not the same pair charged with launching the attack on Sergei Skripal, were detained in the Hague in spring and sent back to Russia.
Accredited by the Organisation for the Prohibition of Chemical Weapons (OPCW), the institution has been charged with testing substances used in Salisbury, Amesbury and Syria.
A spokesperson for the Swiss Federal Intelligence Service (NDB) told The Independent that authorities “are aware of the case of Russian spies discovered in the Hague and expelled from the same place”.
“The Swiss Federal Intelligence Service (FIS) participated actively in this operation together with its Dutch and British partners,” she added. ”The FIS has thus contributed to the prevention of illegal actions against a critical [part of] Swiss infrastructure.”
Officials at the Spiez Laboratory said it had also been targeted with cyber attacks, including a fake conference invitation that contained malicious software.
The spies, who were allegedly found with espionage equipment that could be used to spy on the laboratory, were sent back to Russia and have not been prosecuted.
Spiez became the centre of conspiracy theories spread by Russian state media earlier this year, which falsely claimed that western-made BZ nerve agent and its precursors rather than novichok were found in the Skripal samples.
Foreign minister Sergei Lavrov used the claims to turn fire on Britain by accusing it of producing BZ and violating the chemical weapons convention.
Ahmet Uzumcu, the former head of the OPCW, later said a precursor chemical of BZ and a blank sample was sent to all designated laboratories alongside real evidence taken from Salisbury to prove their tests were accurate.
“The BZ samples did not have anything to do with the Salisbury samples,” he added in May. “It was solely for checking the quality of the work.”
Russia has been seeking to discredit OPCW’s verification of chemical weapons used in Salisbury and Syria, where it is supporting Bashar al-Assad’s forces.
The Kremlin has used its power of veto at the UN Security Council to block any resolutions against the Syrian government, while the Russian Embassy in London has claimed the OPCW “lacks transparency”.
Tensions with Britain have risen yet again after the government identified the two men accused of launching the Salisbury novichok attack as Russian spies from the GRU military intelligence agency.
On Friday, a Kremlin spokesman suggested that it would not allow British access to the suspects.
“We don’t organise interviews with citizens of Russia,” Dmitry Peskov said: “There are mechanisms to provide legal assistance... if the British decide to make an application, we will respond strictly according to law.”
Police released images of the men last week and said they arrived in Britain two days before the poisoning on business visas and genuine Russian passports in the names of Alexander Petrov and Ruslan Boshirov.
Two men claiming to be the suspects appeared on the state-funded RT television network on Thursday after Vladimir Putin publicly called on them to give an interview.
They claimed the suspected aliases were their real names and said they visited Salisbury two days in a row to see its “famous” cathedral – even though CCTV showed them walking in the opposite direction towards Mr Skripal’s house on both days.
The men explained their extensive travel history around Europe, which is now the subject of close scrutiny, by claiming to be businessmen selling sport nutrition supplements.
The pair also denied they were carrying novichok, or were in possession of a specially adapted Nina Ricci perfume bottle UK police say was used to administer the poison.
Security minister Ben Wallace told the House of Commons that they smuggled the novichok into Gatwick airport using the counterfeit bottle, which was “recklessly” discarded after being used to smear the nerve agent on Mr Skripal’s front door and later poisoned Charlie Rowley and killed his partner Dawn Sturgess.
A Downing Street spokesman dismissed the suspects’ interview as “lies and blatant fabrications”, which were an “insult to the public’s intelligence”.
“More importantly, they are deeply offensive to the victims and loved ones of this horrific attack,” he added. “Sadly, it is what we have come to expect. An illegal chemical weapon has been used on the streets of this country.
“We have seen four people left seriously ill in hospital and an innocent woman has died. Russia has responded with contempt.”
Sajid Javid has vowed that Britain and its allies will catch the pair if they ever leave Russia again using European Arrest Warrants and Interpol red notices, but admitted the scenario is unlikely.
“If they ever step out of the Russian Federation, Britain and its allies will get them and we will bring them to prosecution,” the home secretary said on Saturday, claiming the GRU was “getting its instruction directly from the highest level of the Russian government”.
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