British police investigating the poisoning of Alexander Litvinenko with a radioactive cup of tea in London have revealed they were also poisoned in what they think was a Russian-backed attack.

Officers from Scotland Yard were sent to Moscow to investigate the men suspected of poisoning Mr Litvinenko, a former KGB agent and critic of the Russian government.

Former detective inspector Brian Tarpey, who led the investigation, said members of his team were poisoned during a visit to the prosecutor general’s office.

Window still seeking justice for Alexander Litvinenko ten years on

In the Channel 4 documentary Hunting the KGB Killers, Mr Tarpey says: “I had a cup of tea and we left.

“I started to feel uncomfortable; not wanting to put too fine a point on it, I had the sh**s.

“We were probably poisoned with something like gastroenteritis. I think there was a deliberate ploy to weaken us physically because we were the decision makers in the team.”

The Litvinenko files: Was he really murdered? Show all 8 1 /8 The Litvinenko files: Was he really murdered? The Litvinenko files: Was he really murdered? Alexander Litvinenko in his hospital bed at University College Hospital, London, shortly before he died © PA The Litvinenko files: Was he really murdered? Russian President Vladimir Putin stands accused of ordering the murder of Litvinenko © AP The Litvinenko files: Was he really murdered? Litvinenko’s widow, Marina, wants an official inquiry into her husband’s death © PA The Litvinenko files: Was he really murdered? Former KGB agent Andrei Luguvoi at target practice © AP The Litvinenko files: Was he really murdered? Litvinenko's funeral took place at Highgate Cemetery in north London in December 2006 © EPA The Litvinenko files: Was he really murdered? Marina Litvinenko listens as Alex Goldfarb reads her husband's final statement in London last November © AFP/Getty Images The Litvinenko files: Was he really murdered? Russian exile, multi-millionaire property magnate, and perpetual thorn in Putin's side, Boris Berezovsky was a constant presence behind the scenes © AFP/Getty Images The Litvinenko files: Was he really murdered? In memoriam: a candlelit tribute to Litvinenko in Helsinki the day after his death © AFP/Getty Images

The Russian embassy declined to answer questions regarding Mr Tarpey’s claims, The Sunday Times reported.