British scientists are monitoring a fourth aircraft for possible radioactive contamination as part of an investigation into the death of former Russian spy Alexander Litvinenko.
The plane, a Boeing 737 leased by Transaero, arrived at Heathrow airport this morning, British Home Secretary John Reid told the House of Commons.
Grounded British Airways jetliner rests at Moscow's Domodedovo airport.
Earlier, it was reported that thousands of anxious British Airways passengers were seeking reassurance from the airline after it confirmed that "very low traces" of radiation had been found on two of its aircraft by police investigating Mr Litvinenko's death.
A third plane is in Moscow awaiting inspection.
The first three planes identified in the scare had been flying around Europe since Mr Litvinenko's death, mostly between Moscow and London but also to destinations like Barcelona, Larnaca and Athens.
It is not clear what routes the fourth leased plane had flown in the last couple of weeks.
British Airways said it had been advised "the risk to public health is low". It has set up helplines to give guidance to an estimated 33,000 passengers on more than 200 affected flights. The numbers are on its website www.ba.com.
Mr Litvinenko, a former Russian spy, died last Thursday of radiation poisoning. Significant amounts of radioactive Polonium 210 were found in his body. An inquest opens on Thursday.
From his deathbed, Mr Litvinenko accused Russian President Vladimir Putin of ordering his death. The Kremlin denies any involvement but the Litvinenko case has fuelled tensions between London and Moscow.
Investors shrugged off concerns that the radiation scare would scare off passengers. BA shares were trading 1.1 per cent firmer at 500-3/4 pence earlier this morning.
But it is another public relations setback for BA, Europe's third-largest carrier, which has suffered four successive summers of disruptions from industrial action and security alerts.