London has blamed Moscow for a plan of trying to put a pro-Kremlin leader to Kiev and Russian intelligence remains in contact with former Ukrainian politicians.
Britain alleged that it had information that Moscow was "looking to install a pro-Russian leader in Kyiv" as fears grow of an invasion of Ukraine.
"We have information that indicates the Russian Government is looking to install a pro-Russian leader in Kyiv as it considers whether to invade and occupy Ukraine," the Foreign Office said in a statement.
The statement also underlined that former Ukrainian MP Yevgen Murayev is being considered as a potential candidate.
UK's Foreign Secretary Liz Truss said that they will not tolerate a plot for new pro-Russian leadership in Ukraine.
"The Kremlin knows a military incursion would be a massive strategic mistake & the UK and our partners would impose a severe cost on Russia," she said on Twitter.
Former politicians with Russian links
British Foreign Office said that it has information that the Russian intelligence services maintain links with numerous former Ukrainian politicians.
Serhiy Arbuzov, Andriy Kluyev, Vladimir Sivkovich, Mykola Azarov are among the politicians who most of them have prime minister experience between 2010-2014, said the statement.
"Some of these have contact with Russian intelligence officers currently involved in the planning for an attack on Ukraine," it added.
Britain has sent anti-tank weapons to Ukraine as part of efforts to bolster its defenses against a potential Russian attack.
Amid diplomatic efforts to defuse the crisis, UK Defence Secretary Ben Wallace is expected to meet Russian Defence Minister Sergei Shoigu for talks in Moscow. No timing has been given for the meeting, which would be the first U.K.-Russia bilateral defense talks since 2013.
Moscow has denied UK's accusation over installing a pro-Kremlin leadership in Ukraine.
"The disinformation spread by the British Foreign Office is yet another evidence that it is the NATO countries, led by the Anglo-Saxons, that are escalating tensions around Ukraine," the Russian foreign ministry said on Twitter.
The ministry also urged the UK to "halt provocative activities."