Russia has threatened to target British factories in a 'semi-military' response to the UK's support for Ukraine, as Vladimir Putin warned that a 'Pandora's box has been opened.'

It comes after Moscow on Monday accused the UK of 'participating in this war' as Prime Minister Andy Burnham arrived in Kyiv for his first foreign visit, where he announced that European defence firm MBDA had been given permission to share information on UK components for the long-range SCALP missile.

The move sparked a furious reaction from the Kremlin, with a senior Putin adviser now warning of a more aggressive response and claiming Russia views the UK as 'evil number one.'

Speaking to Adam Fleming yesterday on BBC Newsnight, former Russian Deputy Foreign Minister Andrei Fedorov said the Kremlin's reaction to Burnham's announcement had been 'very negative', with Putin warning that a 'Pandora's box' was being opened.

Asked about the threat, Fedorov said: 'There's a very serious political and public pressure on President Putin today, to undertake certain measures against UK, because he is considering UK as part of the war in Ukraine, and assistance from the UK is considered as a direct involvement of UK in this war.'

The official warned that a new stage of escalation would see a 'not only verbal but maybe some visible reaction' from Russia towards the UK.

Expanding on what this would look like, Fedorov said: 'It might be so-called technical reaction, maybe some hackers attack from unknown source, not from official level, of course. 

'There might be different political steps. And I cannot exclude 100% that there might be some semi-military, for example.

He clarified that British factories producing drones for Ukraine could be targeted in such a move, by 'unknown sources.'

Hackers would also target what he described as 'concrete enterprises' linked to the production of drones or components for Storm Shadow missiles. 

Fedorov explained that by Burnham handing over blueprints for the manufacturing of missiles in Ukraine, Britain has become 'much more involved' in the war. 

'Moscow is considering steps by UK prime minister as direct military involvement into this conflict,' he added.  

Fedorov's comment come after Kremlin spokesman Dmitry Peskov claimed earlier on Monday that 'Britain is participating in this war' on the side of Ukraine. 

'Britain methodically and regularly pours fuel on the fire and methodically and regularly plots to prevent any progress in the peace process.'

He added that the Russian armed forces were intent on identifying 'the production sites of such missiles, the production sites of other military equipment' in order to destroy them.

But Burnham insisted there would be no let-up in the UK's support for Ukraine against Vladimir Putin's aggression, branding Russia's threats to the UK 'outrageous'.

'Who started the fire? That's the question, isn't it,' he said.

It emerged over the weekend that the Russian ambassador has been withdrawn from London as relations deteriorate even further. 

The UK's decision means the 'deep precision' Scalp – which is built using both British and French technology – could now be produced locally in Ukraine.

The weapons are critical for long-range strikes reaching targets deep inside Russia.

Giving a speech in front of St Sophia cathedral in Kyiv to mark the 35th anniversary of Ukraine's independence, Burnham compared the country's resistance to the fight against Nazi Germany.

'My nation kept the flame of European freedom alive in the 20th century, you hold that flame in the 21st,' he said.

'Despite Russia's outrageous threats to my country, we will continue our support for Ukraine.'

In his first major speech on the international stage, Burnham praised the 'sheer strength' of the Ukrainian people as 'truly awesome', and said that 'this is the moment to keep up the pressure on Russia, the moment to squeeze their ability to fund this illegal war'.

'Ukraine has been Europe's protector, not a drain on our security but the front line in keeping Europe safe,' he added.

'The Ukrainian people deserve not just our continued support, but our gratitude and respect,' he said, thanking Ukrainians for 'the incredible stand' they have taken.

Burnham also chaired his first meeting of the 'coalition of the willing' on Monday afternoon.

In an apparent message to Donald Trump, he told the group of allies that Ukraine needed more Patriot interceptor missiles immediately to 'help to protect its people'.

He also called on the US Congress to 'ratchet up' economic pressure on Russia.

Burnham said Russia's economy was struggling with a record budget deficit and declining oil revenues as he backed a sanctions bill proposed by the late Republican senator Lindsey Graham.

The Kremlin has warned of 'consequences' over UK drones being used by Ukraine to strike far into Russia.

Moscow said the deeper Britain became involved, 'the higher price it will pay'.

Burnham said: 'On Ukraine's 35th anniversary of independence, its people should be in no doubt: The UK is behind you.

'In the fight and the rebuilding to come, we stand with Ukraine. Russia should be in no doubt of our resolve. We will not back down till there is a lasting peace.'

But Russia said relations with Britain are at 'an unprecedentedly low level' as it ordered its ambassador Andrey Kelin back to Moscow after seven years in post.

Kelin has accused the UK of choosing 'a path of confrontation' with Russia.

Burnham said: 'Russia should be in no doubt of our resolve. We will not back down until there is a just and lasting peace.'