Rishi Sunak has denied holding back on sending fighter jets to Ukraine - as his predecessor Boris Johnson clamours for Typhoons to be sent immediately.
The Prime Minister is under pressure to bow to requests by Ukrainian president for high-tech planes that will help protect the war-torn country from Russian "terrorists".
Today Ukrainian President Volodymyr Zelensky made a passionate plea for more weapons to fight off Vladimir Putin's forces, and at a press conference in Dorset warned that without more equipment the country faces "stagnation".
An awkward-looking Mr Sunak insisted that "nothing is off the table", but said the length of time it takes to train pilots to fly sophisticated warplanes is a stumbling block.
This afternoon Boris Johnson dismissed Downing Street's insistence that it's not practical, telling LBC: “The important thing now is that his message is heard. What he’s asking for is the tools to finish the job – that’s all he wants.
“He just wants the ability to use the long-range missiles - the deep fryers as they’re called - to take out Putin’s positions and he wants the ability to keep his country safe with more tanks and planes.
"His appeal was very, very interesting for the focus he put on aviation and on planes.”
Addressing journalists through a translator, Mr Zelensky said that without the fighter jets he is asking for there is a risk of "stagnation".
He said: "Now we've come to kind of this stagnation phase.
"You've just asked me what would happen if we don't get these fighter jets or longer-range missiles, or we don't have enough ammunition, because everything obviously is running out and coming out of maintenance.
"Without the weapons that we are discussing now and the weapons that we just discussed with Rishi earlier today and how Britain is going to help us, you know, all of this is very important. Without this, there would be stagnation which will not bring to anything good."
Standing alongside Mr Zelensky, Mr Sunak said this evening: "Nothing is off the table."
But there was no announcement that the desired fighter jets were being supplied, with the PM saying it takes three years to train a pilot to fly a "sophisticated piece of kit".
He hit back at critics, saying: "I don't think there's a reticence at all."
The Prime Minister said: "There is a supply chain around such sophisticated aircraft.
"Those are conversations that the president and I are having and making sure we understand all the supply chain needs that go alongside aircraft like that - making sure they can be used and used safely, kept safely. So we are having that conversation.
"And it is also a conversation we are having with our allies because, particularly some of the aircraft we have, are done through joint treaty with multiple other countries - I think we have seen that with previous bits of kit that others have had to give.
"For aircraft, that is something we are also involved in because, as I said, we have other allies involved in the provision of those bits of equipment.
"And as the president said, he is on his way to Europe after this to pick up this conversation with our partners and allies over there."
Earlier today Mr Zelensky used a speech in Westminster Hall to make an impassioned plea for warplanes.
Hundreds of MPs, peers, staff and journalists applauded and cheered as he arrived in the historic Westminster Hall to make a speech, the first foreign leader to do so since ex-US President Barack Obama gave a speech there in 2011.
In a passionate address, Mr Zelensky praised the "brave souls" of the UK for their support on behalf of his people.
"I have come here and stand before you on behalf of the brave, on behalf of our war heroes who are now in the trenches under enemy artillery fire," he said.
"On behalf of our air gunners, and every defender of the sky who protects Ukraine against enemy aircraft and missiles, on behalf of our tank men who fight to restore our Ukrainian borders, on behalf of our conscripts who are being trained now including here in Britain."
Mr Zelensky said London had "stood with Kyiv since day one" and he praised ex-PM Boris Johnson, who was in the audience, for helping to unite allies when "it seemed impossible".
His speech was repeatedly met with applause ringing through ancient hall as he said: "We know freedom will win.
"We know Russia will lose. And the victory will change the world - a change the world has long needed."
Ahead of the visit, the Prime Minister announced plans to train Ukrainian pilots to allow them to fly sophisticated NATO-standard fighter jets - a key demand from Ukraine.
The Ukrainian leader used his speech to strengthen his pleas for the West to provide fighter jets for his forces, saying: "I appeal to you and the world with simple and yet most important words: combat aircraft for Ukraine, wings for freedom."
He gave a nod to the Royal Family's military background, saying: "The King is an Air Force pilot. And in Ukraine today, every Air Force pilot is a king.”
