LONDON, England - December 7, 2010 – Special Air Services (SAS) hit squads are today protecting packed shopping centers from terrorists - with orders to shoot to kill.

The regiment's elite troops are poised to foil any al-Qaeda bid to cause Mumbai-style carnage amid Britain's Christmas crowds.

The Who Dares Wins teams have instructions to strike hard and fast to combat the "real and credible" threat of a bomb-and-gun onslaught by fanatics.

The crack SAS troops are equipped with weapons including high-velocity Minimi semi-automatic assault rifles, gas-loading pistols and stun grenades.

They have been briefed to "engage and neutralize" any terrorists as quickly as possible to minimize the chance of civilian deaths. They know the first 90 minutes are crucial to prevent the toll soaring.

The alert comes after growing fears that fanatics inspired by al-Qaeda plan a copy of the 2008 outrage in Mumbai, India.

Police stepped up security at shopping centers and airports across Britain over the weekend because of the fear of such an attack.

The SAS were brought in because of the potential threat to shoppers on the streets of London, Birmingham and other major cities.

British police firearms teams - such as the Met's CO19 unit - are highly trained to deal with gunmen who pose a threat.

But SAS expertise would be needed to handle a large-scale terror incident.

The Sun has revealed that civilian workers at the Met's three 999 emergency call centers have been briefed on how to deal with a "mass shooting".

If the SAS are called into action, it will be their first operation launched on British soil since the Iranian Embassy siege in London in 1980.

Five of six terrorists were killed and 19 hostages saved.