Air passengers will not be allowed to opt out of body scanning operations at airports, the Government announced today.

But future equipment to be used will mean machines, rather than security staff, will see the images of passengers, Transport Secretary Justine Greening said.

And she added that airports will be tested to ensure they remain "unable to copy, save or otherwise transmit images".

Ms Greening also said that she would consider carefully the EC report on the health risks of scanners, amid concerns that the backscatter scanner, which is being trialled at Manchester airport, emits ionising radiation.

Manchester, with Heathrow and Gatwick, has been trialling body scanners following the Christmas Day transatlantic flight incident when a would-be terrorist had an explosive device concealed in his underwear.

In a Parliamentary written statement, Ms Greening said she believed, in principle, that scanners should be rolled out more widely at UK airports.

But she added that the precise timing of future installations of such devices would depend on how quickly the new generation of scanners was developed.

She said that following a consultation on scanners, the overwhelming feedback from airports was that nearly all passengers accepted the use of scanners and that the Government was only aware of 12 refusals among more than a million scans.

She went on: "Most responses to the consultation expressed discomfort with the idea of having an image of their body captured for analysis, and they indicated that - if selected for a security scan - they would prefer to opt for an alternative method of screening. I have considered this carefully. However, I have decided against it, on security, operational and privacy grounds.

"I do not believe that a 'pat down' search is equivalent in security terms to a security scan. The purpose of introducing security scanners in the first place was to protect the travelling public better against sophisticated terrorist threats: these threats still exist and the required level of security is not achieved by permitting passengers to choose a less effective alternative."

Ms Greening said passengers selected for scanning would not be able to fly if they were not willing to be scanned.

She added that the Health Protection Agency had found the dose of ionising radiation received from backscatter scanners was "the equivalent to that received naturally through just two minutes of flying at high altitude".

On computers, rather than security staff, seeing the scanned body image, Ms Greening said: "Software which automatically analyses images is currently in development.

"Where this technology has developed to a stage at which it passes rigorous Government testing, airports will be expected to deploy it when they renew or replace their equipment.

"This will mean that, in the future, images will no longer be seen by human reviewers."