Treasury minister Darren Jones has said the UK government's commitment to Ukraine is "resolute" amid fears incoming US President Donald Trump could push the country into giving up territory to Russia.
Jones told OceanNewsUK's Sunday with Laura Kuenssberg, "Ukraine should be able to recover its country as it was previously structured" and that there "shouldn't be an element of conceding to illegal invasions from Russia".
He added he would not comment on "hypothetical scenarios" of a future US administration.
Speaking to the same programme, Conservative shadow foreign secretary Dame Priti Patel said the UK had to find a "shared way of working with the US" on Ukraine.
During the election campaign, Trump characterised the Russia-Ukraine conflict as a drain on US resources and said he could end the war between Russia and Ukraine "in a day".
The president-elect has not offered details of how he would resolve the conflict,
However, a research paper written by two of his former national security advisers has argued that the US should continue its weapons supply to Ukraine, but make the support conditional on Kyiv entering peace talks with Russia.
To entice Russia, the West would promise to delay Ukraine’s entry into Nato, the military alliance of European and North American nations.
The former advisers argued Ukraine should not give up its hopes of getting its territory back from Russian occupation, but that it should negotiate based on current front lines.
Asked how the UK government would respond if Trump did compel Ukraine to make territorial concessions, Jones said: "Our commitment to Ukraine as a country here in the UK is resolute.
"We continue to support Ukraine with billions of pounds of funding every year and support from our armed forces in line with our commitments through Nato."
Asked if the UK still respected Ukraine's desire to get back territories such as Crimea, Jones said: "That is the basis on which the UK is operating."
Dame Priti, who was appointed shadow foreign secretary earlier this week, agreed Ukraine should not have to concede Crimea.
“No, of course not," she said adding: "We’ve been unequivocal as Conservatives in government… we stand shoulder to shoulder with Ukraine."
She added that Trump “hasn’t entered the White House yet” and it would be wrong to speculate on future US foreign policy.
"I think, take one step back, let’s be mature about this.
"We need to have dialogue and this comes back to having a strong relationship with our closest ally.
"I would urge our government going forward to be constructive in those discussions."
Speaking to the same programme, Chief of the UK Defence Staff Sir Tony Radakin said Russia had suffered its worst ever month for casualties since the start of the Ukraine war, with around 1,500 dying or wounded every single day.
Sir Tony said the losses were "for tiny increments of land" but that there was "no doubt that Russia is making tactical, territorial gains and that is putting pressure on Ukraine".
"Russia is spending over 40% of its public expenditure now on defence and security - that is an enormous drain on Russia as a country.
"I’m saying the longer the war goes on, the more difficult it is."
He reiterated the UK government's stance that Western allies would be resolute for "as long as it takes" adding: "That’s the message President Putin has to absorb and the reassurance for President Zelensky."
Former Labour minister Lord Peter Mandelson said: "Whatever happens to the fringes of Ukraine territory - and in that I don’t think anyone should be dictating to the Ukrainians what they do - what is sacrosanct is their freedom. That’s not up for grabs."
He said the UK should work with the US to secure Ukraine's freedom and its borders to ensure Russia "can't invade again".
He added that would be possible, not by offering Ukraine Nato membership, but by building "stronger, deeper" economic relationships with the country.
There have been reports that Lord Mandelson could be appointed the UK's new ambassador to the United States.
Asked if he was in the frame for the high-profile position, he said: "Nobody has spoken to me about this job."
On whether he would be interested, he said he would be "very interested indeed in giving advice about trade to whoever is appointed".
In addition to criticising the amount the US is spending to support Ukraine, Trump has also repeatedly urged Nato members to spend more on their own defence, accusing European countries of free-riding on America.
Nato countries are expected to spend 2% of their national income on defence. At the moment 23 countries - including the UK - meet the target, compared to just six in 2021.
The Labour government has committed to increasing spending from 2.3% to 2.5% - but has not set a date for hitting the figure.
Jones said the government would not commit to a deadline until it had completed its strategic defence review into the current state of the armed forces.
