The government insisted on Thursday there is no threat to security from foreign employees working "airside" at airports without having had their backgrounds checked for criminal convictions.
BBC 2's "Newsnight" programme broadcast late on Wednesday, said it had discovered what it described as the "serious loophole" in the law regarding foreign workers.
For the past five years, criminal background checks have been required for all UK staff in restricted zones at airports.
About 200,000 people work airside in British airports, although it remains unclear how many are foreigners.
After originally saying it was too complex to check criminal records from abroad, the government later defended its procedures.
"The terrorist threat to aviation from airside workers is fundamentally addressed by physical security measures, for all staff, every day," the Transport Department said in a statement.
"In addition to physical security, we run a counter-terrorist check, which is far more detailed than a criminal record check, for all airside workers engaged in security roles."
A review of aviation security is due to report back in the summer, it added.
But Conservative Shadow Home Secretary David Davis said the loophole needed to be closed immediately.
"It's astonishing given the history and, of course, the risk on the airside of any airport in the United Kingdom," he told Newsnight.
"To not do anything about it because it's inconvenient, it's a disgrace. They should immediately carry out security checks on all people currently working airside."
In December, a Muslim woman who called herself the "Lyrical Terrorist", was convicted for writing religious poetry praising attacks on "non-believers".
Samina Malik, 23 - who worked at a newspaper shop airside at Heathrow airport - was sentenced to eight months jail, suspended for 18 months.
