Ukrainian President Volodymyr Zelensky has urged the UK to provide his country with fighter jets as he addressed Parliament during his first UK visit since Russia's invasion of Ukraine.
In an impassioned plea, he likened combat aircraft to "wings for freedom".
His call comes as the UK announced it will begin training Ukrainian forces to fly Nato-standard fighter jets.
President Zelensky concluded his speech with the hope that he would soon be thanking the UK for providing planes.
Later, Downing Street said Prime Minister Rishi Sunak has asked the defence secretary to investigate what jets the UK could potentially give to Ukraine, but emphasised it was "a long-term solution".
Addressing a huge crowd of MPs and peers in the historic setting of Westminster Hall, Zelensky said: "Freedom will win - we know Russia will lose," adding the UK was with his country on a march to "the most important victory of our lifetime".
Thanking the UK for its "grit", he said the country, through its support of Ukraine, had not compromised the "spirit and ideals of these great islands".
He also singled out Boris Johnson for praise saying the former prime minister had united others "when it seemed impossible".
During his speech, which was met throughout with applause, the Ukrainian leader gave the House of Commons Speaker Sir Lindsay Hoyle the helmet of a Ukrainian pilot.
The writing on the helmet reads: "We have freedom, give us wings to protect it."
Reflecting on his last visit to the UK, he recalled thanking his hosts "for delicious English tea".
"I will be leaving Parliament today, thanking you all in advance for powerful English planes."
Johnson echoed his calls in a statement saying: "It is time to give the Ukrainians the extra equipment they need to defeat Putin and to restore peace to Ukraine. That means longer range missiles and artillery, it means more tanks, it means planes."
BBC defence correspondent Jonathan Beale says that while the president gave an impassioned plea for Britain to give Ukraine fast jets, it still doesn't look likely that he'll get them, at least for now.
He said it was still possible that a few Western nations could provide a small number of modern fighter jets to Ukraine at some time in the future, and that while Kyiv had made clear it would like US made F-16s, which are operated by a number of Nato countries, so far US President Joe Biden had said no.
As the first anniversary of Russia's invasion approaches, the UK has announced that its training of Ukrainian forces will be expanded to cover marines, as well as Nato-standard fighter jet pilots.
Western countries have been considering how to bolster support for Ukraine, with the country braced for a renewed Russian offensive later this month.
The expansion of the UK's training programme signals a shift, after the UK said it was "not practical" for it to send its aircraft to Ukraine.
Earlier this year, the UK also announced it would send 14 battle tanks to Ukraine. Zelensky praised Sunak for taking this "powerful defensive step".
In his address, he also urged the UK and the West to continue imposing sanctions "until Russia is deprived of any possibility to finance the war".
"Anyone who invests in terror must be held accountable, anyone who invests in violence must compensate those who have suffered from terror."
On Wednesday, the UK announced a fresh round of sanctions targeting Russia.
The latest sanctions target IT companies, as well as manufacturers of military equipment such as drones and helicopter parts.
Before speaking to Parliament, Zelensky held talks with Sunak in Downing Street, and has met King Charles.
He was expected to join the prime minister on a visit to the south-west where Ukrainian troops are training to use Challenger 2 tanks.
The two men will sign the London Declaration - a statement affirming the UK-Ukraine partnership - before holding a joint press conference.
Later, he is expected to meet French President Emmanuel Macron and German Chancellor Olaf Scholz at the Elysee Palace in Paris.