Two women, thought to be airport workers, have been arrested
Police in Britain are investigating a scam involving airside security passes at Heathrow Airport.
They have arrested two women, thought to be airport workers.
Heathrow said it had "taken appropriate action" until the police investigation is complete.
Scotland Yard would not reveal details of their suspicions around airside passes, but it is not thought to involve their illegal sale or cloning.
It could be part of a criminal plot - Heathrow was dubbed 'Thiefrow' after a string of thefts - but it will inevitably raise concerns about terrorism.
Kevin Hurley, former head of counter terrorism at the City of London Police, said: "It could be used to get close up to some of the high-value cargo areas and of course we have already had the Brink's Mat saga here once before.
"Billions go through this airport every year. But the real issue is the threat in terms of airport security; this is a potential serious breach for Heathrow Airport."
Lax airside security is thought to have allowed terrorists to put a bomb on a Russian passenger flight that blew up killing all 224 on board shortly after taking off from Sharm el-Sheikh in Egypt last year.
Evidence emerged after the launch a fortnight ago of a Heathrow fraud investigation and the questioning of the two suspects who were arrested on suspicion of fraud and money laundering.
The concern is believed to be around the processing of passes, which are issued to many of the airport's 70,000 workers employed on the airport's airside.
Permanent and temporary passes are given to flight crews, baggage handlers, shop and restaurant staff, hangar and ramp workers, cargo and security employees.
Holders are subject to strict vetting, including five years of employment references without gaps.
When they enter airside they are subject to the same security procedures as passengers, including metal-detector checks and the removal of shoes and belts.
Heathrow said: "We can't comment on the specifics of an ongoing police investigation.
"Our top priority is the security and safety of our passengers and colleagues and we have taken appropriate action until the investigation is completed."
The UK Department for Transport said: "We are aware of this issue. Safety and security of passengers is our priority.
"We keep aviation security under constant review, but as this matter is the subject of an ongoing police investigation we are unable to comment further at this time."
Scotland Yard said it arrested two women, aged 24 and 20, last week and bailed them until November.
A spokesperson said: "They have been arrested in relation to an allegation that money has been fraudulently taken from a bank account. Other matters have come to light during the enquiries and form part of the ongoing investigation."