The SAS are on our streets following the Paris attacks
Co-ordinated attacks in the French capital saw the gunmen and suicide bombers target a music venue, a football match at the Stade de France and several popular restaurants and bars.
Six of the terrorists blew themselves up and one was shot by the police during the atrocity which President Francois Hollande called an “act of war”.
Three accomplices are believed to have escaped and be on the run.
Many Britons were among the dead and UK military experts fear it could “inspire” jihadis to target the UK.
At least 352 people are thought to have been injured, 99 critically, in what was one of the the worst acts of violence on French soil since the Second World War.
Some 1,500 extra troops were deployed to the streets of Paris after a state of emergency was announced.
Tight controls have also been introduced at the French borders.
Last night Britain was stepping up its security with the SAS brought in to counter a potential attack.
Units were called in by the Counter Terrorist Command wing of the Metropolitan Police to provide extra covert surveillance of key targets and an armed response.
It followed high-level meetings with senior intelligence officers from the Joint Terrorist Analysis Cell at MI5.
More than 60 soldiers, including personnel from the SAS and the Special Reconnaissance Regiment, were last night operating under the direction of the Met’s CTC wing.
An unarmed unit of soldiers has been deployed to infiltrate key “areas of interest” known to contain jihadi sympathisers.
Another tranche, armed with nuclear, biological and chemical equipment, will be at a military base “within striking distance” of London, on call to respond to a major terror attack.
“It comes as no surprise that there have been calls for increased security along those lines.”
Met Commissioner Sir Bernard Hogan-Howe said: “The public can be reassured that our firearms officers are trained to deal with this kind of incident and we are constantly evolving new ways to combat the threats to public safety.”
President Hollande, who will no longer be attending next week’s G20 summit in Turkey, said the attacks were “committed by a terrorist army, the Islamic State, a jihadist army, against France, against the values we defend everywhere in the world, against what we are: a free country that means something to the whole planet”.
He said France “will be merciless toward the barbarians of Islamic State” and “will act by all means anywhere, inside or outside the country”.
Earlier Islamic State claimed responsibility, saying “brothers wearing explosive belts and carrying assault rifles” had targeted “the capital of abominations and perversions and those who carry the crusader banner in Europe”.
Last night it emerged one of the Paris attackers had entered Europe through Greece on a Syrian passport only a month ago.
The horror took place between 9pm and 10.30pm on Friday.
Six separate attacks were co-ordinated by the terrorists, who were operating in three teams.
There were three explosions outside the Stade de France, the first at 9.20pm, when a suicide bomber and a football fan standing next to him were blown up.
At least 14 people were then killed at Le Carillon bar and Le Petit Cambodge restaurant on Rue Albert and another four died in a shooting on nearby Avenue de la Republique.
At least 80 were killed after gunmen brandishing AK47s stormed the Bataclan theatre where California rock band the Eagles Of Death Metal were playing.
The men began targeting 100 hostages one by one before killing themselves when police entered the building.
A witness said one gunman shouted “Allah Akbar” and “This is for Syria”.
Two of the attackers at the theatre committed suicide with explosive vests and one was shot by police.
In Downing Street the Union Jack was at half mast last night alongside a French Tricolore in a show of solidarity.
The Queen yesterday sent a message to President Hollande, saying: “Prince Philip and I have been deeply shocked and saddened by the terrible loss of life in Paris. We send our most sincere condolences to you, the families of those who have died and the French people.”
He warned people to prepare for news of more British casualties.
“The British and French people stand together as we have so often before in our history when confronted by evil. We must be prepared for a number of British casualties,” he said.
“We are doing all we can to help those caught up in the attack. They were killed and injured by callous murderers who want to destroy everything our two countries stand for: peace, tolerance, liberty. But we will not let them. We will redouble our efforts to wipe out this poisonous, extremist ideology. Your fight is our fight.”
Defiant Parisians yesterday queued for hours to donate blood.
Carole Bagot, donations organiser at the Etablissement Francais du Sang, said: “On a normal Saturday we would have 40 people. Today it was hundreds. We were open from 8am to 3.30pm and had to turn people away and ask them to go to another centre or return another day.”
One donor, William Haddad, 29, said: “We belong together. We have to be strong. We have to fight with everything we have, with our health and with our blood.”
The attacks come after the Charlie Hebdo atrocity in January, which saw 12 people killed as gunmen stormed the Paris offices of the satirical magazine.
They also came a day after Islamic State militant Mohammed Emwazi, known as Jihadi John, was targeted in a US air strike in Syria.
The Foreign Office has advised Britons to “exercise caution in public places”.