Britain has offered to send tanks to Poland so it can supply its own heavy weaponry to Ukraine for its battle with Russia.
Boris Johnson revealed plans to “backfill” military support for Ukraine as he warned that the war could continue until next year - and Russia could win.
The Government has resisted sending its own tanks straight to Ukraine over fears it would escalate tensions with Russia.
But it is understood that sending equipment to Warsaw is regarded as the quickest way to support Ukraine.
The plan would allow Poland to then send on Soviet-era T-72 tanks, which Ukrainian troops are trained to use, to Kyiv.
Western allies are also preparing to offer security guarantees to Ukraine so it is "impregnable" to a future Russian invasion, the PM revealed.
At a press conference in New Delhi today, the Prime Minister said: “We are looking more at what we can do to backfill in countries such as Poland, who may want to send heavier weaponry to help defend the Ukrainians.
“We are looking at sending tanks to Poland to help them as they send some of their T72s to Ukraine.”
He said Ukraine needed to be a part of Europe’s security plans - but stopped short of offering Nato-style assurances which means an attack on one state is regarded as an attack on all.
"What the Ukrainians want - and I think are now going to get - is a collection of guarantees from like-minded countries about what we can do to back them up with weaponry, with training and with intelligence-sharing," he said.
"It will, I hope, enable the Ukrainians to offer deterrence by denial and make sure their territory is so fortified as to be impregnable to further attack from Russia.”
Western officials today warned the war in Ukraine could continue until the end of this year and Russia could ultimately triumph.
Asked about the assessment, Mr Johnson said: “The sad thing is that that is a realistic possibility.
“Of course Putin has a huge army, he has a very difficult political position because he has made a catastrophic blunder.
“The only option he now has is to continue to use his appalling, grinding approach, led by artillery, trying to grind the Ukrainians down.”
But he added: “I think no matter what military superiority Vladimir Putin may be able to bring to bear in the next few months - and I agree it could be a long period - he will not be able to conquer the spirit of the Ukrainian people."
Despite his words of support for Kyiv, No10 accepted that Mr Johnson did not press Indian Prime Minister Narendra Modi to harden his stance against Russia during talks today.
The Prime Minister’s official spokesman said Mr Johnson did not raise India's neutrality on the Russian invasion at the UN during his meeting in Delhi.
“He was not there to talk to another democratic country about what actions they should take,” the spokesman said, adding that this approach would not be “constructive”.
Indian Foreign Secretary Harsh Vardhan Shringla said the leaders “did discuss the Ukraine issue but there was no pressure.”
"Prime Minister Johnson shared his perspective on it, Prime Minister Modi shared ours - which is that the Russia-Ukraine war should end immediately. There was no pressure of any kind.”
The PM told the press conference: ”The position on Russia that the Indians have historically is well known. They are not going to change that, of course, that's true.
"But they can see what is going on and there is an increasing appetite to do more with the UK."
Meanwhile, it emerged that Mr Johnson refused to use a Russian-built helicopter to visit a factory in Gujarat owned by a Tory donor.
Officials vetoed use of the Mi-17 chopper to carry the PM to the JCB factory near Vadodara, instead using a US-built Chinook from an Indian Air Force base, according to the Times of India.
