Armed Police At Wembley / Special Forces told to shoot to kill
Armed police from SCO19 will be standing guard at the football match between England and France being held tonight at Wembley Stadium. The move follows attacks in Paris on Friday, which included bomb attacks at a football match. 
Security will be tight at the match, which will be attended by Prince William. There will be armed officers present in the stadium and patrolling outside. Police will also be out in force on the major rail routes bringing fans to Wembley.
The match takes place amid a security operation the likes of which London has not seen since the 7/7 bombings 10 years ago. Armed British Transport Police have been deployed to transport nodes such as the Eurostar terminal at St Pancras station and undercover policemen and soldiers from the Special Reconnaissance Regiment are operating on the capital's streets. 
Although no specific threat has been made against the event, tensions remain high as security chiefs ponder how to best protect the country against the kind of simultaneous multi-facetted attacks carried out in the French capital.
The Mail reports that Special Forces have been ordered to 'shoot to kill' terrorist gunmen. Armed Police units, such as SCO19, have also been given orders to take quick action against terrorists.  In a change from the established doctrine of containment and negotiation, intervention forces are now being directed to carry out an immediate action in order to neutralise the terrorist threat and save lives.
This strategic change in response reflects a change in the terrorist gunmen's strategy. Recent times have seen them moving away from the hostage-taking and negotiation for political concessions that characterised much of the terror incidents since the 1970s. Actions such as those in Mumbai in 2008 and Paris in 2015, involving groups of gunmen attacking civilians, require an immediate and deadly response by the security forces on hand. The old days of the Police setting up a cordon around a siege and waiting for the SAS to drive down from Hereford are over, it would seem.
The SAS, it has been reported, keeps a number of troops from the counter terrorism team within the capital so as to more quickly respond to an incident. 
SCO19, for its part, has beefed up its counter terrorism capability in recent years. It has developed teams of Counter Terrorist Specialist Firearms Officers (CTSFO) specifically to be better able to deal with hostage rescues and terrorist gunmen.
More info / further reading
- 1. Prince William vows to attend tomorrow night's match between England and France 'in show of solidarity' as armed police are ordered to guard Wembley
(The Daily Mail)
- 2. Special Forces On London Streets After Paris Attacks
(Elite UK Forces report)
- 3. SAS unit moves to London in terror fight
- 4. Scotland Yard creates SAS-style unit to counter threat of terrorist gun attack