The BBC is investigating whether an online leak of the final episode of the TV series Sherlock was the work of Russian hackers.

Titled His Final Problem, the fourth season finale and rumoured to be the show’s last episode, was illegally uploaded to the internet on Saturday.

The leaked version of the 90-minute episode was dubbed in Russian and featured a continuity announcement identifying it as broadcast by Russian state-owned Channel One.

The BBC said it was investigating the leak, tweeting: “We are aware that Sherlock episode 3 has been uploaded illegally online. If you come across it, please do not share it.”

Over the weekend, the show’s producer Sue Vertue confirmed the leak had come from Russia.

“Russian version of Sherlock TFP has been illegally uploaded. Please don’t share it. You’ve done so well keeping it spoiler free. Nearly there,” she wrote.

Several UK newspapers and think tanks have suggested the cyber-attack could have political motives.

The Telegraph wrote on Sunday that “the Kremlin is thought to have been angered by a recent decision to expand the BBC World Service’s Russian language output”.

If proven true, it could be another episode on the ongoing cyber war between Russia and the West, after reports of Russian hackers breaking into Democratic Party servers.

The British broadcaster is reportedly working with Channel One in Russia to understand how the Sherlock episode, broadcast on Sunday, found its way online.

A preview screening of the series finale was also held last Thursday in London for journalist and television critics.

Creator Steven Moffat has suggested another series of the detective drama “was possible” despite the rumours the His Final Problem would be the last episode.

The show, based on the novels by Sir Arthur Conan Doyle, stars Benedict Cumberbatch as Sherlock and Martin Freeman as his sidekick Dr John Watson.