Armed soldiers have been stationed in Whitehall amid fears that terrorists will try to attack ceremonial guards in the wake of the shooting in Canada.
The soldiers, who are carrying assault rifles, have been deployed at the entrance to Horse Guards Parade, where thousands of tourists gather each day to witness the Changing of the Guard.
The decision follows a review after a Canadian soldier on ceremonial duty was shot dead last week in a suspected terrorist attack.
There are growing concerns that British jihadists fighting in Syria and Iraq will return to this country and carry out terrorist acts.
Senior police officers and MPs said there is likely to be a significant rise in the number of armed police at the Remembrance Sunday and Armistice Day commemorations next month.
One senior counter-terrorism police officer said that there will also be a large number of officers operating undercover at the events, carrying Heckler and Koch side arms.
Richard Dannatt, the former head of the armed forces, said: “It is a sad sign of the times but discreetly guarding soldiers on ceremonial guard is a far better option than withdrawing them from duty and sight.