Teenage girls who fear they are being taken abroad to enter into a forced marriage are using a simple trick to escape: hiding a spoon or any other metal object in their underwear to set off the metal detector at the airport and avoid the flight at the last minute.

A charity has said it knows of many girls who have escaped what they fear awaits them in their family’s old homeland, by using the ruse to be separated from their parents.

The revelation follows a Government warning to teachers, doctors and airport staff to be alert to the problem that school age girls who are seemingly being taken abroad on holiday may actually be on their way to a life of enforced servitude.

Download the new Independent Premium app Sharing the full story, not just the headlines

Forced marriages are particularly common during the summer holiday break, when there is a minimal chance of a child’s absence being noticed. The Foreign Office’s Forced Marriage Unit received 400 reports in the three months up to the end of August last year, though it is feared that many more cases go unreported. More than a third of those affected are under 16.

Karma Nirvana, a Derby-based charity which runs a helpline for victims of forced marriages, has been encouraging desperate teenagers to try the spoon trick. Its founder, Jasvinder Sanghera, was disowned by her Sikh family at the age of 16 after she refused to marry a man in India. She set up the charity in 1993, when she was 27.

The charity takes about 600 calls a month. “When youngsters ring, if they don’t know exactly when it may happen, or if it’s going to happen, we advise them to put a spoon in their underwear,” charity spokesman, Natasha Rattu, said.

She added: “When they go through security, it will highlight this object in a private area and, if 16 or over, they will be taken to a safe space where they have that one last opportunity to disclose they’re being forced to marry.

“We’ve had people ring and say that it’s helped them and got them out of a dangerous situation. It’s an incredibly difficult thing to do with your family around you – but they won’t be aware you have done it. It’s a safe way.”

Almost half of the 1,500 cases a year handled by the Forced Marriage Unit involve Pakistan. Bangladesh counts for 11 per cent, and India eight per cent, the remainder being spread across about 60 countries, including Afghanistan, Somalia, and Turkey. The youngest victim they have come across was aged two, the oldest was 71.

Sameem Ali, a Manchester city councillor, was forced into a marriage in Pakistan when she was 13, and was brought back to the UK months after she became pregnant, aged 14.

She told BBC Breakfast: “I did not know I was going to get forced into a marriage until a week before the marriage actually occurred. I had never seen the guy before. I was in the middle of nowhere and I did not know where I was.”

Another woman, whose identity was protected by Essex Police, told AFP that her father forced her into a marriage in India, after threatening to find her and kill her if she tried to run away.

“I was shipped off with a total stranger. That night I was raped by my husband and this abuse continued for about eight and half years of my life,” she said. She later escaped.