A BITTER rival of Russian President Vladimir Putin has been caught romping with a British-raised activist in a sex sting.

Married former Prime Minister Mikhail Kasyanov, 58, was tipped as one of the few opposition leaders capable of toppling Putin.

But last night his career was hanging by a thread after a grainy 40-minute video of him and a female anti-Putin playwright was shown on Russian state TV.

The footage showed Kasyanov, who fell out with Putin after serving as PM, in a steamy bedroom clinch with Natalya Pelevine, 39.

The pair were filmed naked or wearing little, their faces fully visible. They were seen embracing, with Pelevine, who grew up in Britain, wearing a bra, knickers, stockings and suspenders. The black-and-white film did not show explicit sex acts.

Pelevine accused Kasyanov’s family of stealing state assets. He replied: “I buy for five kopeks (cents) and sell for five roubles.”

Kasyanov claimed he was doing the same as Russian oligarchs but “they act on a different scale”.

The politician was also overheard saying how he needed to target a fellow anti-Putin candidate, Alexei Navalny, before parliamentary elections later this year.

In September Russians go to the polls with wages at their lowest since Putin first came to power 16 years ago.

Changes in the law mean the President can seek a fourth term in office in 2018.

Yesterday Kasyanov refused to comment. Pelevine said she will sue NTV.

Kasyanov, who has two children, works with Pelevine — also known as Natalya Pelevina — who acts as his aide in his RPR Parnas party.

Pelevine was born in the old Soviet Union, but her parents emigrated to Britain when she was still a child.

The video was billed as “Kasyanov Day” on the NTV channel.

A presenter told viewers: “A man resembling Mikhail Kasyanov, the leader of RPR Parnas, is meeting a woman resembling Parnas member Natalya Pelevina, but there is no doubt that it is Kasyanov and Pelevina.”

Sources last night said the sting smacked of a classic operation by Russia’s FSB, the successor to the KGB. It appeared to have been secretly filmed using a camera hidden in a dressing table inside a Moscow flat used by the couple.

They were also heard talking about Kasyanov’s links to corruption.