Last week, Indian authorities told MI5 about a suspected plot by militants linked to al Qaeda in Pakistan to hijack an Air India or Indian Airlines flight from Mumbai or Delhi.
The warning, which came after the capture of a suspected Islamic leader, was contained in a detailed "threat assessment" sent to MI5 by the Indian Intelligence Bureau.
Meanwhile, the Indian Government has increased passenger screening and frisking at all main airports and is deploying additional armed sky marshals to deal with the threat.
British Home Secretary Alan Johnson revealed on Friday, Jan 22, that the threat level to UK was being raised from "substantial" to "severe", which means that a terror attack is "highly likely".
The official terror threat was at the severe level for four years after the July 7 bombings in London in 2005. It was downgraded last Jul 2009.