Ukraine's state security service SBU detained Yezhov on suspicion of working in the interests of Russia, Prime Minister Volodymyr Groysman said today. Pictured: Groysman (left) with Theresa May at No 10. Behind them, circled, is Yezhov

An interpreter who visited 10 Downing Street in July has been arrested in Ukraine on suspicion of spying for Russia.

Stanislav Yezhov - an interpreter for the Ukrainian cabinet - was detained by the country's police today.

In a shocking Facebook post, Ukraine's prime minister Volodymyr Groysman said that Yezhov had 'long been working in the interests of a hostile government'.

It is not known, however, if he is accused of spying at the time he attended Downing Street in July.

Asked about the man visiting Downing Street, Mrs May told a press conference in Poland: 'I am aware of the reports in relation to a Ukrainian individual who attended Downing Street earlier in the summer.

'The matter is for the Ukrainian authorities.'

Asked whether he would raise the issue of the alleged spy during talks with Mr Lavrov in Moscow on Friday, Mr Johnson said: 'I think that is a matter for the Ukrainians.

'We want Ukraine to go on the right path and we are worried that Ukraine needs more encouragement, more help, to reform, to make sure it isn't captured by the wrong influences.

'I think possibly what this episode shows is the real difficulties and risks that the Ukrainian government is running. They need a lot of encouragement.'

Ukraine's state security service SBU detained Yezhov, 39, on suspicion of working in the interests of Russia, Prime Minister Volodymyr Groysman said today.

'Together with the Security Service of Ukraine, an official in the government's secretariat was found to be working for a long time in the interests of the enemy state. He was detained,' Groysman said on Facebook.

Stanislav Yezhov - an interpreter for the Ukrainian cabinet - was detained by the country's police today

A Downing Street spokesman said: 'Security at Number 10 is kept under constant review.' Pictured left: Alleged spy Yezhov outside Downing Street. Right: Yezhov (highlighted) with Boris Johnson

A Foreign Office spokeswoman said: 'We are aware of reporting about the arrest of Stanislav Yezhov in Ukraine.' Pictured: Yezhov on board a plane

Ukraine's state security service SBU detained Yezhov, 39, on suspicion of working in the interests of Russia, Prime Minister Volodymyr Groysman said today. Pictured: Yezhov being led away by police

Mrs May said today that Britain and Poland are concerned about Russian attempts to weaponise information. Pictured: Yezhov hanging his head while being taken away by police

Oleksiy Petrov, head of counterintelligence in Ukraine, told Pryamiy TV: 'The official had access to insider information about the Cabinet of Ministers'. Pictured: Yezhov being led away in handcuffs today

Yezhov's home and workplace are now being searched by Ukrainian security services, they indicated. Pictured: Yezhov in front of a Ukrainian flag

Yezhov was seen being led away in handcuffs on Ukrainian television.

Ukraine's security service said Yezhov acted 'on the orders' of Russia to collect information 'about the activities of government structures', with the help of 'special equipment'.

Yezhov gave data to the Russians through 'electronic channels of communication', the security service said.

His home and workplace are now being searched by Ukrainian security services, they indicated.

A Downing Street spokesman said: 'Security at Number 10 is kept under constant review.'

Oleksiy Petrov, head of counterintelligence in Ukraine, told Pryamiy TV: 'The official had access to insider information about the Cabinet of Ministers.

'He was respected. And he responsibly and diligently worked for the Russian special services.'

He also met then-US Vice President Joe Biden in 2016.

Neither the PM nor the SBU named the position or name of the detained official, but he has been widely named as Stanislav Yezhov.

The SBU said in a statement that the official was recruited by Russian agents while he travelled abroad. It said the official had been collecting information about the activities of the government.

Asked about the man visiting Downing Street, Mrs May told a press conference in Poland: 'I am aware of the reports in relation to a Ukrainian individual who attended Downing Street earlier in the summer. Pictured: May with Polish PM Mateusz Morawiecki today

Ukraine and Russia were once allies whose intelligence agencies often worked closely together, but relations deteriorated after Russia's annexation of Crimea in 2014 and support for pro-Russian separatists in eastern Ukraine.

Mrs May said today that Britain and Poland are concerned about Russian attempts to weaponise information.

'We have agreed today to bolster our cooperation to counter Russian disinformation in the region .... we are both deeply concerned by Russia's attempts to weaponise information,' she told reporters during a visit to Poland.

The revelation came as Foreign Secretary Boris Johnson travelled to Moscow for a meeting with Russian counterpart Sergey Lavrov tomorrow. Pictured: The foreign secretary in Poland today

'The Kremlin is seeking to undermine the international rules-based system and it will not succeed.'

The revelation came as Foreign Secretary Boris Johnson travelled to Moscow for a meeting with Russian counterpart Sergey Lavrov tomorrow.

It comes at a time when relations between Moscow and the West are at their coolest for several decades.

A Foreign Office spokeswoman said: 'We are aware of reporting about the arrest of Stanislav Yezhov in Ukraine.

'We can neither confirm or deny the allegations against him. It is not our practice to comment on legal proceedings in other jurisdictions.'