POLICE have foiled a major plot to "commit mass murder on an unimaginable scale" by destroying up to ten passenger jets in mid-air.The targets were flights leaving UK airports to the US.

POLICE have foiled a major plot to "commit mass murder on an unimaginable scale" by destroying up to ten passenger jets in mid-air.

The targets were flights leaving UK airports to the US.

Anti-terror police arrested 21 people in London, the Thames Valley and Birmingham last night as stringent new security measures were imposed on all UK airports.

Metropolitan Police Deputy Commissioner Paul Stephenson told reporters at New Scotland Yard that the plot was designed to cause "untold death and destruction''.

He added: "This was intended to be mass murder on an unimaginable scale.''

Searches were on-going at a number of addresses, he added.

Sources indicated that the majority if not all of those arrested were British.