Defence Secretary Ben Wallace is leading work with allies which could see Britain send tanks to Ukraine, No10 said on Wednesday.
Downing Street said the UK was looking to “accelerate” its support to Kyiv to help it “win this war” against Vladimir Putin’s regime.
It said tanks could be a “game-changing capability”, amid reports that Britain is considering supplying a dozen Challenger II tanks.
The Prime Minister’s official spokesman said: “We are accelerating our support to Ukraine with the kind of next generation military technology that will help win this war.
“It’s clear that battle tanks could provide a game-changing capability to the Ukrainians.
“The Prime Minister told President Zelensky last week the UK will provide whatever we can.
“The Prime Minister has asked the Defence Secretary to work with partners in the coming weeks to discuss how we can go even further and faster on our support to Ukraine including the provision of tanks.”
Kyiv is also seeking German-built Leopard II tanks.
Western officials believe that Ukraine will not be able to seize back significant territory from Russia without an increase in military capability, including tanks and armoured vehicles.
Ukrainian diplomats say they need hundreds of tanks to achieve a decisive breakthrough in the war which Putin launched last February.
Ukrainian president Volodymyr Zelensky and Putin are seeking to build up their armed forces for a major spring offensive.
One western official said that a reported Ukrainian call for 300 tanks was “not an unreasonable number” to create the force mass needed for them to go on the attack.
“The Ukrainians won’t be unable to win back significant amounts of territory without changes to their force posture from last year. The force ratios between the Russians and the Ukrainians are too finely balanced,” the official said.
“Something needs to break that deadlock, especially if they (the Ukrainians) are to win territory back and go on the offensive. Main battle tanks and APCs (armoured personnel carriers) are part of that mix.
“I think the Ukrainians would look to all partners who might provide tanks won’t be particularly worried about where they come from just so long as they come in sufficient volume.”
The German government is not aware of any requests from its allies to send Leopard battle tanks to Ukraine, said a government spokeman in Berlin on Wednesday.
Germany is coordinating closely with the United States, France, Britain and other allies on military support for Ukraine, he added.