"Boris Johnson has been the frontman for this policy, but it's whole-of-British-government policy," said Peter Ricketts, a former UK national security advisor and ambassador to France.

"Whoever was prime minister would have done much the same thing," although "Johnson brought his own particular style to it," Ricketts added.

Former French ambassador to Britain Sylvie Bermann agreed that though "the line will remain, the style will be different".

With impassioned speeches and editorials and two visits to Kyiv since Russia's February 24 attack, on top of arms deliveries, Johnson won admiration from Ukrainians.

"Johnson, despite the domestic scandals, has been solid in his support for Ukraine," tweeted Alina Polyakova, head of the Washington-based Center for European Policy Analysis, adding that "as a friend told me, 'he is like a god in Ukraine'".

Conversely, Moscow was among the first foreign capitals to react Thursday to news of Johnson's impending departure.

"We would like to hope that some day in Great Britain more professional people who can make decisions through dialogue will come to power," Kremlin spokesman Dmitry Peskov told reporters.

"He really does not like us. And we (do not like) him either," Peskov said of Johnson.

Where other nations have been content to let the British melodrama play out, Russia had been stung by London's early decisions to send lethal aid, including more than 5,000 anti-tank missiles, to Ukraine.

In late June, Britain decided on a new military aid package worth pound1 billion ($1.2 billion) including air defence systems and drones -- bringing its total to pound2.3 billion.

Announcing he would step down from the leadership of the Conservatives Thursday, Johnson spared a line for Ukraine, saying "we in the UK will continue to back your fight for freedom as long as it takes".

- 'Seeking the spotlight' -

Ukrainian President Volodymyr Zelensky called Johnson to express his "sadness" over his resignation.

"We all welcome this news with sadness. Not only me, but also all of Ukrainian society," the presidency quoted Zelensky as saying.

"We don't doubt that Great Britain's support will continue, but your personal leadership and your charisma made it special," he said.

Zelensky adviser Mykhaylo Podolyak thanked the UK leader in a tweet for "always being at the forefront of supporting Ukraine".

Former French diplomat Bermann said: "Johnson wanted to look like he was out in front, or 'leading the world', as he would say."

But "it's not at all the true picture," she said.

Johnson "is constantly seeking the spotlight, it's true that it's very nice for Zelensky to have unconditional support, but beyond that, the UK didn't play a role that stood out particularly from others".

Ricketts said: "There's been a bit of one-upmanship in the British approach, in being determined to show the other Europeans that we can do more."

"The UK has been one of the leaders, but all of that's dwarfed by... the Americans," he added, calling Washington's response "off the scale in terms of anything the Europeans have done, including Britain".

Russia's invasion came as Johnson was plagued by domestic woes, including long-running action over Downing Street parties during Covid lockdown and the allegations about sexual harassment within his governing Conservative party that finally brought him down.

He was accused at home of using his relationship with Zelensky to score points, with many journalists and other observers joking on social media that each new scandal would prompt a visit or phone call to Kyiv.

"He has capitalised on the war to distract attention from his other problems," Ricketts said.

Nevertheless, although "Johnson established a good personal link with Zelensky... there's no reason to doubt that that would be handed on to another prime minister," he added.

"I think Zelensky would be friends with anyone who's useful to him."