Russia has only achieved "international isolationism and humiliation" from its invasion of Ukraine, Defence Secretary Ben Wallace said.
In a bold statement, Mr Wallace said the retreat of Vladimir Putin's invading forces from the key city of Kherson marks "another strategic failure" after Russia failed to achieve any of its key goals other than taking the city.
It comes as the retreat is said to have cause "panic" in Russian ranks.
Mr Wallace said in a statement today: “Russia’s announced withdrawal from Kherson marks another strategic failure for them. In February, Russia failed to take any of its major objectives except Kherson.
“Now with that also being surrendered, ordinary people of Russia must surely ask themselves: ‘What was it all for?’
“The Russian army has suffered a huge loss of life as a result of their illegal invasion and have only achieved international isolationism and humiliation. Ukraine will press on.
“The UK and the international community will continue to support them, and while the withdrawal is welcome, no one is going to underestimate the continuing threat posed by the Russian Federation.”
The Russian retreat from Kherson marks the end of one of the bloodiest battles in the war so far.
The retreat is said to have cause "panic" in Russian ranks, according to one an adviser to the Ukrainian defence minister. but cautioned the war is “far from over”.
Yuriy Sak told BBC Radio 4’s Today programme: “We always believed that we will liberate Kherson.
“And we are confident that now Russians are beginning to believe that they will never be able to win this war.
“We see the panic in their ranks. We see the panic in their propaganda machine.
“But of course, this is a very important moment, but it is too early to relax… because this war is far from over.”
He added: “At the moment we are quietly optimistic. We are beginning to carry out stabilisation measures in Kherson but of course we understand that there are future battles which we will have to win.”
On Saturday, the White House praised Ukraine's "extraordinary" victory.
National security advisor Jake Sullivan said: “It does look as though the Ukrainians have just won an extraordinary victory where the one regional capital that Russia had seized in this war is now back under a Ukrainian flag - and that is quite a remarkable thing."
“It’s a big moment and it’s due to the incredible tenacity and skill of the Ukrainians, backed by the relentless and united support of the United States and our allies."
The withdrawal from a regional capital in the south of Ukraine brings “significant reputational damage”, defence experts have said.
British intelligence analysts believe Moscow’s exit from Kherson, a strategically key city, likely began as early as October 22 when Russian-installed figures urged civilians to leave.
Following Russia's withdrawal from the city, videos and pictures posted on social media later showed residents celebrating in the streets, with the Ukrainian flag flying over a central Kherson square.
Kherson was one of the first Ukrainian cities to be captured in the war Moscow waged on its neighbour from February 24.
The retreat, which was ordered amid a Ukrainian counter-offensive, represents a huge blow to president Russian president Vladimir Putin – who has so far remained silent on the development.
Ukraine is yet to claim the city is back in Ukrainian hands, but the country’s president Volodymyr Zelensky said “life is returning”.
Russian forces still control about 70% of the wider Kherson region in the wake of the withdrawal.
The UK Ministry of Defence (MoD) tweeted to say Moscow’s troops had “highly likely” destroyed road and rail bridges over the Dnipro River as part of their retreat.
The exit was formally announced on November 9, but the defence experts said it is likely it started as early as October 22.
“There is a realistic possibility that Russian military equipment and forces in civilian attire had been evacuating in conjunction with the 80,000 stated evacuated civilians in recent weeks,” they said.
The MoD said is it probable Moscow is still attempting to evacuate forces from other parts of the region across the river to defensible positions on the eastern bank.
“Kherson was the only regional capital city captured since February by Russian forces so the withdrawal brings significant reputational damage,” it said.
“The withdrawal is a public recognition of the difficulties faced by Russian forces on the west bank of the Dnipro River.
“It is likely that Ukraine has retaken large areas of Kherson oblast on the west bank of the Dnipro River, and that its forces are now largely in control of Kherson city itself.”
