Sky marshals will soon be travelling on British passenger planes as part of the war against terrorism.

Downing Street confirmed that specially armed officers will soon be patrolling domestic and international UK flights from the New Year but officials have refused to give further details.

"For very obvious reasons we are not going into details of when, where and how," said the official spokesman.

A new security team made up of police and intelligence officers, modelled on how Israel protects its flights, has been developed as part of the response to the US terror attacks.

"The capability has been developed. the training is in place," said the spokesman.

The revelations followed warnings that al Qaeda suspects had been operating in the UK and the assessment by officials that Britain will eventually be the victim of a terrorist outrage by people with links to the group.

Some airline bosses have expressed concern at the development but Number 10 stressed the high level of training of the new security team.

"We understand people's reservations but equally these people will be specially trained. This is not taking a bobby off the beat and putting him on a plane," said Number 10.