It is now compulsory for people selected for a scan to take part, or they will not be allowed to fly.

The new security rules have been introduced following the attempt to blow up a plane over Detroit on Christmas Day.

There have been concerns the scanners breach passengers' rights to privacy.

Transport Secretary Lord Adonis said in the immediate future only a small proportion of airline passengers would be selected for scanning.

In a written statement to the House of Commons, he said: "If a passenger is selected for scanning, and declines, they will not be permitted to fly."