The fraught relationship between Russia and the West, which was supposed to improve following an agreement over Ukraine, has descended instead into renewed acrimony after a series of tense military and diplomatic confrontations.

France and Germany, which had brokered the Minsk accord last week, were yesterday trying to hold together the increasingly fragile ceasefire in Ukraine amid reports that fighting was spreading once again. Kremlin-backed separatists and Cossack fighters triumphantly paraded through the shattered town of Debaltseve, a strategic point they had captured in the past 48 hours.

Britain, which along with the EU will be strongly criticised by a House of Lords committee today for “sleep-walking into this crisis”, was drawn towards centre-stage after two Russian Bear bombers off the coast of Cornwall – but just outside UK airspace – were met by RAF jets scrambled from their base in Coningsby, Lincolnshire.

The apparent probe of British readiness came soon after the Defence Secretary, Michael Fallon, accused President Vladimir Putin of trying to extend his campaign of destabilisation to the Baltic countries. The Russian leader, he said, presented as much of a threat to Europe as Isis.

David Cameron said Moscow was trying to make “some sort of point” by its repeated deployment of planes close to British airspace, adding: “I don’t think we should dignify it with too much of a response.”

Weary Ukrainian servicemen leave the area around the besieged town of Debaltseve in eastern Ukraine on Wednesday after fierce combat with pro-Russian rebels (Reuters)

Russia reacted with fury at Mr Fallon’s remarks, however. Deputy Foreign Minister Alexander Lukashevich declared that his comments were “already beyond diplomatic ethics”, adding: “The characterisation of Russia is completely intolerable. We will find a way to respond to the comments.”

But Mr Fallon received support at home and abroad for his warning on Moscow’s intentions. Valdis Dombrovskis, the vice-president of the European Commission, and a former Prime Minister of Latvia, said: “Russia’s aggression against Ukraine is very worrying for Baltic states. It shows that Russia is looking to redraw Europe’s 21st-century borders by force, and it must be noted that Ukraine is not the first country to face Russian aggression.”

Lithuanian Foreign Minister Linas Linkevicius said: “Russia is behaving aggressively now as we speak. I really do see threats to all countries, If we fail to act now to what’s happening in Ukraine, there will be a big temptation [for Russia] to further instigate situations elsewhere.”

Latvia’s Finance Minister, Janis Reirs, said that his country had already detected elements of “hybrid warfare” against his nation.

In London, Rory Stewart, the chairman of the Commons Defence Committee, said the West was on a “political razor-edge” over how to balance its response to Mr Putin, weighing the risk of allowing Russian expansionism to go unchecked and triggering further conflicts.

He said: “There’s no doubt at all that probably the most vulnerable part of the Nato alliance at the moment is the Baltic states.”

Dark days ahead? The Freedom Monument in Riga during a partial eclipse of the Sun (EPA)

He urged all British political parties to write into their manifestoes a commitment to spend two per cent of GDP on defence – as required by Nato – to send a message to Mr Putin. He also asked them to prepare to deal with threats such as cyber-attacks, irregular troops, and propaganda.

The EU committee of the House of Lords also argued, in the findings of an inquiry to be published today, that Western Europe failed to detect the real character of the Kremlin. For too long, it said, the relationship had been based on the “optimistic premise” that Russia was on a trajectory to democracy.

The British Government, which is one of the guarantors of the territorial integrity of Ukraine in return for it giving up a nuclear arsenal, was heavily criticised for not being “as active or as visible as it could have been”.

“It [the committee] believes that the EU, and by implication the UK, was guilty of sleep-walking into this crisis,” said the committee chairman, Lord Tugendhat. “The lack of robust analytical capacity, in both the UK and the EU, effectively led to a catastrophic misreading of the mood in the run-up to the crisis.”

Ukraine crisis: A timeline of the conflict Show all 23 1 /23 Ukraine crisis: A timeline of the conflict Ukraine crisis: A timeline of the conflict 30 November 2013 Public support grows for the “Euromaidan” anti-government protesters in Kiev demonstrating against Yanukovych’s refusal to sign the EU Association Agreement as images of them injured by police crackdown spread. EPA Ukraine crisis: A timeline of the conflict 20 February 2014 Kiev sees its worst day of violence for almost 70 years as at least 88 people are killed in 48 hours, with uniformed snipers shooting at protesters from rooftops. AFP/Getty Images Ukraine crisis: A timeline of the conflict 22 February 2014 Yanukovych flees the country after protest leaders and politicians agree to form a new government and hold elections. The imprisoned former Prime Minister, Yulia Tymoshenko, is freed from prison and protesters take control of Presidential administration buildings, including Mr Yanukovych's residence. Genya Savilov/AFP/Getty Imageses Ukraine crisis: A timeline of the conflict 27 February 2014 Pro-Russian militias seize government buildings in Crimea and the new Ukrainian government vows to prevent the country breaking up as the Crimean Parliament sets a referendum on secession from Ukraine in May. Sean Gallup/Getty Images Ukraine crisis: A timeline of the conflict 16 March 2014 Crimea votes overwhelmingly to secede from Ukraine and join Russia in a ballot condemned by the US and Europe as illegal. Russian troops had moved into the peninsula weeks before after pro-Russian separatists occupied buildings. EPA Ukraine crisis: A timeline of the conflict 6 April 2014 Pro-Russian rebels seize government buildings in the eastern cities of Donetsk, Luhansk and Kharkiv, calling for a referendum on independence and claiming independent republic. Ukraine authorities regain control of Kharkiv buildings on 8 April after launching an “anti-terror operation” but the rest remain out of their control. EPA/PHOTOMIG Ukraine crisis: A timeline of the conflict 7 June 2014 Petro Poroshenko is sworn in as Ukraine's president, calling on separatists to lay down their arms and end the fighting and later orders the creation of humanitarian corridors, since violated, to allow civilians to flee war zones. Getty Images Ukraine crisis: A timeline of the conflict 27 June 2014 The EU signs an association agreement with Ukraine, along with Georgia and Moldova, eight months after protests over the abandonment of the deal sparked the crisis. LOUISA GOULIAMAKI/AFP/Getty Images Ukraine crisis: A timeline of the conflict 17 July 2014 Malaysian Airlines flight MH17 is shot down over eastern Ukraine, killing all 298 people on board. Ukrainian intelligence officials claim it was hit by rebels using a Buk surface-to-air launcher in an apparent accident. Ukraine crisis: A timeline of the conflict 22 August 2014 A Russian aid convoy of more than 100 lorries enters eastern Ukraine and makes drop in rebel-controlled Luhansk without Government permission, sparking allegations of a “direct violation of international law”. Reuters/Alexander Demianchuk Ukraine crisis: A timeline of the conflict 29 August 2014 Nato releases satellite images appearing to show Russian soldiers, artillery and armoured vehicles engaged in military operations in eastern Ukraine. Nato Ukraine crisis: A timeline of the conflict 8 September 2014 Russia warns that it could block flights through its airspace if the EU goes ahead with new sanctions over the ongoing crisis and conflict EPA Ukraine crisis: A timeline of the conflict 17 September 2014 Despite the cease-fire and a law passed by the Ukrainian parliament on Tuesday granting greater autonomy to rebel-held parts of the east, civilian casualties continued to rise, adding to the estimated 3,000 people killed Reuters Ukraine crisis: A timeline of the conflict 20 October 2014 A 'tactical missile' explosion at a factory sends blast wave across rebel-held cityof Donetsk YouTube Ukraine crisis: A timeline of the conflict 16 November 2014 The fragile ceasefire gives way to an increased wave of military activity as artillery fire continues to rock the eastern Ukraine's pro-Russian rebel bastion of Donetsk Getty Ukraine crisis: A timeline of the conflict 26 December 2014 A new round of ceasefire talks, scheduled on neutral ground in the Belariusian capital Minsk, are called off AFP/Getty Ukraine crisis: A timeline of the conflict 12 January 2015 Soldiers in Debaltseve were forced to prepare heavy defences around the city; despite a brief respite to the fighting in eastern Ukraine, hostilities in Donetsk resumed at a level not seen since September 2014 AFP/Getty Ukraine crisis: A timeline of the conflict 21 January 2015 13 people are killed during shelling of bus in the rebel-held city of Donetsk Reuters Ukraine crisis: A timeline of the conflict 24 January 2015 Ten people were killed after pro-Russian separatists bombarded the east Ukrainian port city of Mariupol AP Ukraine crisis: A timeline of the conflict 2 February 2015 There was a dangerous shift in tempo as rebels bolstered troop numbers against government forces AFP/Getty Ukraine crisis: A timeline of the conflict 11 February 2015 European leaders meet in Minsk and agree on a ceasefire in eastern Ukraine beginning on February 14. From left to right: Belarus President Alexander Lukashenko, Russian President Vladimir Putin, German Chancellor Angela Merkel, France's President Francois Hollande and Ukrainian President Petro Poroshenko. MAXIM MALINOVSKY | AFP | Getty Images Ukraine crisis: A timeline of the conflict 13 February 2015 Pro-Russian rebels in the city of Gorlivka, in the Donetsk region, fire missiles at Ukrainian forces in Debaltseve. Fighting continued in Debaltseve for a number of days after the Minsk ceasefire began. ANDREY BORODULIN | AFP | Getty Images Ukraine crisis: A timeline of the conflict 18 February 2015 Ukrainian soldiers repair the bullet-shattered windshield of their truck as their withdraw from the strategic town of Debaltseve. Following intense shelling from pro-Russian rebels, Ukrainian forces began to leave the town in the early hours of February 18. Brendan Hoffman | Getty Images

Western governments stressed that continuing fighting risked the breakdown of the Minsk agreement, but the language was markedly muted. The US administration has put on hold a decision on whether or not to supply the Ukrainian government with heavy weaponry; White House spokesman Eric Schultz said: “What was agreed to last week was not a shopping list.”

Nato insists measures have already been taken to counter Russian aggression in the Baltic and eastern Europe, with bases in the area manned by Allied troops.

Kremlin officials have complained that the move breaches an agreement, made during Boris Yeltsin’s presidency, that Nato would not set up military bases in former Warsaw Pact states close to Russia’s borders.