No 10 said there is a “plethora of evidence” showing Volodymyr Zelensky’s troops have used UK-supplied weapons successfully and minsters fully expected them to continue.
The Kremlin has sought to downplay the significance of the UK’s move to supply increasingly more advanced weapons to aid the resistance.
Spokesman Dmitry Peskov said “these tanks are burning and will burn just like the rest”, claiming the supplies were an attempt to draw out the conflict.
But Rishi Sunak’s official spokesman said: “We have seen very clearly that the Ukrainian armed forces have been very effective with the equipment that we have provided to them.
“I think there is a plethora of evidence for that and we are confident they will do so again.”
Mr Sunak tweeted: “We’re accelerating our support to Ukraine with the most significant UK package of combat power to date.
“Working intensively with our allies and partners, we will ensure Ukrainians can defend themselves, press their advantage, win this war and secure a lasting peace.”
The Prime Minister hopes the UK’s intensifying support will increase the pressure on Russian president Vladimir Putin and galvanise support among Western allies.
We believe that a long and static war only serves to benefit Russia. That's why we are surging our military support
Prime Minister's spokesman
He signed off on sending 14 British Army Challenger 2 main battle tanks to Kyiv, as well as around 30 AS90 self-propelled guns during a call with Ukrainian leader Mr Zelensky over the weekend.
Mr Sunak’s spokesman said: “We believe that a long and static war only serves to benefit Russia. That’s why we are surging our military support.
“The Prime Minister and ministers are speaking to our allies across the world in the following days and weeks to ramp up the pressure on Putin and to secure a better future for Ukraine.”
Mr Zelensky said “tanks, APCs and artillery are exactly what Ukraine needs to restore its territorial integrity” and thanked Mr Sunak, Defence Secretary Ben Wallace and the “British people for this powerful contribution to our common victory over tyranny”.
Mr Sunak’s spokesman said they are “confident” allies will act in a “co-ordinated way”.
Foreign Secretary James Cleverly spoke to Ukraine’s foreign affairs minister Dmytro Kuleba and “confirmed his readiness to work together on persuading other nations to provide Ukraine with western-type tanks”, according to Mr Kuleba.
“We also discussed new sanctions on Russia’s missile and drone industry aimed to put an end to Russian missile terror against civilians,” the Ukrainian official tweeted.
Mr Cleverly and Mr Wallace will meet allies to discuss further military support for Kyiv.
Next month will mark the first anniversary of Mr Putin’s invasion, but Western analysts believe he is preparing for a drawn-out war.
The duration combined with continued atrocities was increasing the pressure to support Ukraine’s resistance.
Authorities on Monday said the death toll from a Russian missile strike on an apartment building in Dnipro had risen to 40.
Rescuers were working to locate victims and survivors in the wreckage of the strike on a multi-story building that housed around 1,700 people in the south-eastern city.
Meanwhile, Mr Cleverly welcomed being among multiple Cabinet ministers and the Army’s Chief of the General Staff, Sir Patrick Sanders, who have been sanctioned by Russia.
“Good,” the Foreign Secretary tweeted in response to Moscow’s move over the weekend.
“If this is the price for supporting Ukrainian freedom, then I’m happy to be sanctioned #SlavaUkraini.”