The plane is among three grounded by the airline as part of the investigation into the radioactive poisoning death of former Russian spy Alexander Litvinenko in London.
Litvinenko was poisoned by the rare radioactive element, polonium 210, and investigators are looking into radioactive traces founded on two other British Airways planes that have traveled the Moscow-London route since Nov. 1, when Litvinenko is believed to have been poisoned.
Britain's Health Protection Agency said Thursday night that it had confirmed that passengers on one of two planes grounded at London's Heathrow airport had not been put at risk and the plane had now been cleared to fly again, but officials were still monitoring the possible exposure of passengers on the other.
It was unclear how the traces of radiation had found their way on board the planes, reports AP.
The press office of British Airway's Moscow office said the British government had allowed the Boeing-767 currently parked at Moscow's Domodedovo airport to return to London on Friday.