Passengers flying to the USA from all airports, including the UK, face the threat of chaos as airlines implement extra security checks before they board flights.

From today all US-bound flights are being forced to comply with new security measures demanded by Washington in return for scrapping a ban on taking laptops onto a flight.

Under the crackdown specially trained security experts hired in from private firms could patrol passenger queues asking people questions about the purpose of their travel.

In addition to having electronic devices screened by machine, other measures could see some passengers being asked asked to turn their phones and laptops off to prove they have not been modified for terrorist purposes.

To minimize delays it is believed that the questioning will be carried out as passengers queue to check in or while they are queuing for security.

Airlines which fly from the UK to the US said passengers did not need to arrive more than the standard two hours before their flight. It means that if the new system does not go as planned passengers could find it takes them longer than expected to get through the airport and onto flights.

A spokesman for the Transportation Security Administration, the US body which is implementing the crackdown, told the Daily Telegraph: “We cannot discuss specific timelines or measures, but some were required immediately, while others will be implemented over time.