The Kremlin had for some time followed a formula of selecting individuals in business or politics and then using those people to "promote Russia's interests", said Podolyak.
"This British information clearly follows along in this logical chain," he added.
London said it had seen evidence that several former Ukrainian politicians had maintained links with Russian intelligence services, and that former MP Yevgen Murayev was being considered as a potential leader.
Some of those in contact with Russian intelligence officers were "currently involved in the planning for an attack on Ukraine", the foreign office said in a statement, though did not release details of the evidence.
'New leadership' needed
The United States said the revelations of the plot were "deeply concerning". Moscow dismissed them as "disinformation", and urged London to "stop spreading nonsense."
Murayev, the former MP allegedly touted as a possible leader by Russia, on Sunday wrote on social media that ex-Soviet Ukraine was in need of sweeping political reforms and a new head of state.
"The Ukrainian people need rule of law, peace, sound and pragmatic economic and social policies, and new political leaders," he wrote.
Murayev lost his seat in parliament when his party failed to win five percent of the vote in 2019 elections. He is understood to be the owner of a television channel that was closed last year on allegations it was airing pro-Russia propaganda.
Concerns in Ukraine have been building as tens of thousands of Russian troops mass on Ukraine's border, along with an arsenal of tanks, fighting vehicles, artillery and missiles.
Current fears of a Russian invasion stem from Moscow's annexation of the Crimean peninsula in 2014 and the capture by pro-Kremlin separatists of two self-proclaimed breakaway republics in Ukraine's east.
More than 13,000 people have died in the fighting between government forces and the pro-Russian rebels.
Blinken defends German commitment
Pope Francis said Sunday he was following "with concern" the rising tensions and called for a day of prayer for peace next week.
That appeal came on the back of a week of talks between US Secretary of State Antony Blinken and Washington's allies in Ukraine and then Berlin, before a meeting Friday in Geneva with Russian Foreign Minister Sergei Lavrov.
There was no breakthrough but the US has said it will respond in writing to sweeping security demands put forward by Russia in the end of last year.
Blinken on Sunday said he had "no doubts" Germany was maintaining a united front with NATO on the Ukraine crisis, after Berlin faced pressure to toughen its stance on the Russian threat to Ukraine.
Germany's navy chief Achim Schoenbach resigned late Saturday in the diplomatic fall-out of his comments to a think tank a day earlier.
Schoenbach had said it was "nonsense" to think Russia was about to march into Ukraine and that president Vladimir Putin deserved respect.
That had prompted Kyiv to summon Germany's ambassador to protest, with tensions between the countries already high over Berlin's decision not to supply weapons to Kyiv.
On Sunday, Blinken told NBC television, "I can tell you that the Germans very much share our concerns and are resolute and being determined to respond -- and to respond swiftly, effectively, and in a united way. I have no doubts about that."