BRITISH troops will join Nato forces in Europe to help defend Ukraine if Russia dares to invade, Boris Johnson vowed last night.
The defiant PM warned that any incursion will spark the worst bloodshed in Europe since World War Two and “many Russian mothers’ sons will not be coming home”.
Mr Johnson said the UK and its allies would respond swiftly and “in unison” to any invasion and with severe economic sanctions.
He added: “The British Army leads the Nato battle group in Estonia and if Russia invades Ukraine, we would look to contribute to any new Nato deployments to protect our allies in Europe.”
They are unlikely to be combat troops but ministers refused to rule anything out.
Members of the Nato alliance — including Denmark, Spain, Bulgaria and the Netherlands — are sending more fighter jets and warships to Eastern Europe to bolster defences in the region.
The US has also put 8,500 troops on alert to deploy at short notice, which Russia said caused it “great concern”.
It came as ex-MI6 chief Sir Alex Younger warned he could not see a scenario where Russian President Vladimir Putin “can back down in a way that satisfies the expectations that he has created”.
Mr Putin continues to deny he plans to invade Ukraine.
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But he has a strike force assembled in the region, which includes 127,000 troops, war jets, battleships, missile batteries, artillery and drones.
His forces have also been conducting training drills on land, sea and air.
Meanwhile, Britain’s Armed Forces Minister James Heappey said “significant numbers” of Russian advance forces have already crossed the border as spies.
Missions include covert reconnaissance of key targets for destruction and intelligence gathering on which populations will support and which will resist an invasion.
Airspace above Ukraine is expected to shut down within days as tensions soar.
Last night, a Russian senator vowed to cut off Europe’s gas in response to Mr Johnson’s threat of “coordinated and severe economic sanctions heavier than anything we have done before against Russia”.
Vice Speaker Nikolay Zhuravlev said Moscow would also starve Europe of oil and metal exports if it was barred from using the Swift international payment system, in a move backed by the US and Britain but opposed by Germany.
And MPs warned that war could trigger hundreds of thousands of refugees fleeing west into the EU.
Tory MP Karl McCartney told the Commons yesterday that an EU “distracted and full of infighting” and unable to respond may be “part of Putin’s thinking”.
He warned: “If this massive flow of refugees happens, it may well be the end of the EU.”