John Sweeney claims a Newsnight investigation into the connections between John Whittingdale, the former culture secretary, pictured, and Dmytro Firtash, a pro-Kremlin oligarch, had been shelved

BBC bosses have been accused of pulling the plug on politically sensitive reports into the close links between leading politicians and Russia.

John Sweeney, a BBC investigative reporter, has turned whistleblower and filed a complaint against the corporation with Ofcom, the broadcasting watchdog. He alleges investigations into Labour’s Lord Mandelson, the former Tory cabinet minister John Whittingdale, the Brexit funder Arron Banks, the oligarch Roman Abramovich and the far-right activist Tommy Robinson were all dropped.

He claims that other potential reports into “the pro-Russian sympathies of Labour spin doctor Seumas Milne” were never even commissioned by BBC editors and raises more concerns about Boris Johnson’s links with Russian oligarchs.

In 2014 Milne, who is Labour’s director of strategy and communications, attended a conference in Sochi