Sky's security editor Sam Kiley said transportation police have been advised to terminate days off on Friday and there will be a heavy existence across the capital and Heathrow and Luton airports.
Members of the crisis services have also lately been briefed about how to respond to a Mumbai-design assault on the capital, Sky sources indicated.
The UK's terror menace level continues to be at its second greatest level - significant - though this does not imply an attack is imminent.
In a globe in which intelligence is rarely black and white, the work to avoid a torrorist assault on Britain is a substantial-stakes game of cat and mouse.
Kiley mentioned no modify is being made to the existing terror risk amount - the best level is vital.
"If you look back over modern terrorist attacks and terrorist attempts, a great deal of them have been fairly amateurish and there has been not too long ago an work by al Qaeda supporting groups to get a grip on that and come up with a lot more sophisticated methods of building bombs and without a doubt evading security services," he stated.
Members of the public have been warned to be on alert for terrorism.
A Residence Office spokesman mentioned: "There is a continuing need for every person to remain vigilant and to report any suspicious exercise to the police."
A Scotland Yard spokesman added: "The menace level to the United kingdom is at significant... and has been since January 2010 ( via news.sky.com ).