Admiral Lord West branded Vladimir Putin “extremely dangerous” as he continues a campaign of “hybrid warfare” to taunt the West.
The former First Sea Lord – who had a 50-year career in the armed forces – described the Russian president as a “crook” and said Putin thinks he can “get away with anything”.
The Royal Navy hero warned conflict woulde be 'catastrophic' and added “no one wants to go to war”, but increasingly unpredictable actions from Russia have led to a 'real risk' of armed conflict.
He called on the world to “get a grip and make some sensible moves” to step back from the brink.
His warning comes as Britain and Russia remain locked in a diplomatic nightmare following the poisoning of Sergei Skripal.
Putin’s diplomats are to be expelled, high level contact cut, and further sanctions imposed on Moscow following the incident last Sunday in Salisbury.
MI6 double agent Skripal and his daughter Yulia, 33, were both left critical after they were allegedly poisoned with military grade Russian nerve agent Novichok.
Both the Prime Minister and defence secretary Gavin Williamson have attacked Russia, demanding answers from the Kremlin on the double attempted murder that poisoned 21.
Russia responded bullishly, refusing to meet an ultimatum and warning Theresa May not to threaten a “nuclear power”.
Speaking exclusively to Daily Star Online, Admiral Lord West said: “For someone to have carried out any attack on our soil is extraordinary.
“And it’s certainly tied to Russia because of the nerve agent used.
“It could killed British people on the street, and in the old days of imperial rivalries nations went to war over things like this.
'This is very very worrying indeed – one has to show [Putin] how serious this as he seems to think its some kind of game.'
Russia has repeatedly denied any involvement and dismissed accusations the Kremlin was behind the attack as fantasy.
Admiral Lord West said if the attack wasn’t orchestrated by Putin, he would certainly have known about it along with high-ranking Kremlin officials.
He detailed how Putin has a previous record of brazen attacks on other states – including cyber attacks, military clashes, and disinformation campaigns to disrupt “free liberal democracy”.
Putin has also been pouring billions into his military, including claiming Russia now has never-before-seen types of invincible nuclear weapons.
While the navy boss said the Russian president would have to be 'barking mad' to want a war with NATO – he added 'the longer one remains a dictator and the longer you get everything you want the closer you get [to being barking mad]'.
Russia's leader has made no secret about his willingness to use nuclear weapons, something the Brit chief branded 'bonkers' and which would 'end up, if we are not careful, in nuclear war'.
Admiral Lord West told Daily Star Online: 'I think at the moment, because of this behaviour, there is a very real risk with the way [Putin] keeps going that by accident something might happen that no one wants.
'It doesn't take much for something like that to escalate – and that would be catastrophic for everyone really.
'That really worries me, everyone needs to get a grip and we need to make some sensible moves.'
He added Putin is targeting Britain as he considers it a rival world power second only to the US – being the number two entity in NATO.
'Putin hates the fact there are powerful liberal democracies around the world, and he would like to see all of those at odds and in a mess,' he said.
He added: 'That would make him very happy.'
He suggested attempting to use international law and bring members of the Russian leadership before the courts might be the best way to tackle 'fire proof' Putin.
'I am afraid that all the indicators are that President Putin doesn't believe that any of the norms of behaviour between international powers apply to him,' Admiral Lord West added.
Putin is now deciding how to respond directly to the UK after Mrs May laid out the sanctions yesterday in Parliament.
His spokesman Dmitry Peskov said that Russia is “perplexed and does not comprehend the British leadership’s stance” and insisted the “accusations are unsubstantiated”.
Leaders of France, Germany, the US and Britain today confirmed the attack 'constitutes the first offensive use' of a nerve agent in Europe since World War Two.