She was stopped along with a man as the pair prepared to board a flight to London after security scans showed up the substance.

Even though specialist examinations later confirmed the liquid was mouthwash, one informed source said its contents may have been much more serious under different circumstances.

"At the right intensity, it could have been something that could have been used in an explosion," said the source.

The couple were detained last Saturday after the alert was raised at the airport's central search area. Both had already been spotted acting 'nervously', it was claimed.

"Someone was looking at the X-ray machines and suddenly picked this up," one airport source told Sunday Life.

"This was kept low-profile until we discovered all the facts."

It is understood the couple only arrived in Northern Ireland a short time before their planned flight out again.

No details of the reason for their visit - or why the woman had strapped mouthwash to her leg - were available this weekend, but both were taken for questioning at Antrim police station.

Detectives had sufficient concerns to hold on to the couple until their travel arrangements were fully checked-out, said one police source.

The couple have now both been allowed to leave Northern Ireland. A police spokesman said last night: "A man and a woman were detained at Belfast International Airport on Saturday evening as part of a routine security check.

"They were later released without charge."

slnews@belfasttelegraph.co.uk