A British former detective who investigated the murder of Alexander Litvinenko has told ITV News he believes he was also poisoned in an apparent attack ordered by the Kremlin.

Brian Tarper, a former detective inspector, believes Russian government officials spiked his tea to unsettle him and colleagues looking into the case.

Litvinenko, a former Russian spy and fierce critic of Putin's regime, was infamously killed in London in 2006 after his cup of tea was poisoned with radioactive polonium-210.

Tarper, who led the murder investigation, has told ITV News of how he believes he was poisoned on a trip to Moscow to question the main suspect in the killing.

Tarper and a colleague paid a visit to the prosecutor general's office.

The Russians had allowed him to interview suspect Andrey Lugovoy - on the condition that they made the recordings.

These tapes were later withheld from Scotland Yard.

Tarper is featuring in the upcoming Channel 4 documentary Hunting the KGB Killers.

A judge-led inquiry found President Vladimir Putin "probably" approved the assassination of Litvinenko.