David Cameron is to meet with UK security chiefs on Monday to discuss whether Britain will give greater powers to its police and spies in the wake of the Paris terror attacks.

The Prime Minister said there were “things to learn” from the wave of violence that saw 17 killed across northern France from Wednesday to Friday – and he has faced pressure to revive the so-called “snooper’s charter” that would make it easier for GCHQ to monitor online communications.

The head of MI5, Andrew Parker, has warned that a group of al-Qaeda terrorists in Syria is planning “mass casualty attacks” against Western targets, while former Royal Navy chief Lord West called for more money to be budgeted to the security service.

In a broadcast interview ahead of his appearance at the unity march in Paris today, Mr Cameron said: “It's important to look at what happened in France and think through those scenarios and other scenarios like them: how we'd respond, how well prepared we are.

In pictures: Reaction to Charlie Hebdo attack Show all 39 1 /39 In pictures: Reaction to Charlie Hebdo attack In pictures: Reaction to Charlie Hebdo attack Reaction to Charlie Hebdo attack Pencils, representing the freedom of expression, placed in tribute in Nantes Reuters In pictures: Reaction to Charlie Hebdo attack Reaction to Charlie Hebdo attack France's Jason Lamy Chappuis soars through the air over a message that reads "Je suis Charlie" Getty In pictures: Reaction to Charlie Hebdo attack Reaction to Charlie Hebdo attack Solidarity in Nice AP In pictures: Reaction to Charlie Hebdo attack Reaction to Charlie Hebdo attack Turkish citizens organised a vigil in front of the French consulate in Istanbul AFP In pictures: Reaction to Charlie Hebdo attack Reaction to Charlie Hebdo attack Graffiti decorates a London wall in solidarity with the victims of the attack in Paris AFP In pictures: Reaction to Charlie Hebdo attack Reaction to Charlie Hebdo attack A tribute of flowers and candles outside the French Embassy in Prague, Czech Republic AP In pictures: Reaction to Charlie Hebdo attack Reaction to Charlie Hebdo attack Messages of sympathy near the Charlie Hebdo office in Paris AFP In pictures: Reaction to Charlie Hebdo attack Reaction to Charlie Hebdo attack Workers install a poster reading 'Je suis Charlie' (I am Charlie) on the Palais des Festivals facade in Cannes In pictures: Reaction to Charlie Hebdo attack Reaction to Charlie Hebdo attack A woman looks at floral tributes left outside the Charlie Hebdo magazine offices in Paris In pictures: Reaction to Charlie Hebdo attack Reaction to Charlie Hebdo attack A woman places flowers near the offices of French satirical newspaper Charlie Hebdo in Paris In pictures: Reaction to Charlie Hebdo attack Reaction to Charlie Hebdo attack Journalists of international press agency Agence France-Presse (AFP) hold signs reading "Je suis Charlie" (I am Charlie) at their headquarters in Paris as they observe a minute of silence for the victims of an attack by armed gunmen on the offices of French satirical newspaper Charlie Hebdo in Paris which left at least 12 dead and many others injured In pictures: Reaction to Charlie Hebdo attack Reaction to Charlie Hebdo attack Pens and pencils are placed in the form of a peace sign over the names of late French cartoonists Cabu, Tignous, Wolinski and late Charlie Hebdo editor Charb on the Place de la Republique (Republic Square) in Paris In pictures: Reaction to Charlie Hebdo attack Reaction to Charlie Hebdo attack Australia mourns victims of the Paris massacre at Federation Square in Melbourne In pictures: Reaction to Charlie Hebdo attack Reaction to Charlie Hebdo attack Indian artist Sudarsan Pattnaik is pictured with his sand sculpture, in tribute of those who lost their lives in the attack by gunmen on French satirical weekly Charlie Hebdo in Paris that killed 12 people, at Golden Sea Beach in Puri, some 65 kilometers from Bhubaneswar In pictures: Reaction to Charlie Hebdo attack Reaction to Charlie Hebdo attack A man holds a placard that reads "I am Charlie" as members of the European Parliament and citizens gather during a minute of silence for victims of the shooting at the Paris offices of weekly newspaper Charlie Hebdo, in front of the EU Parliament in Brussels In pictures: Reaction to Charlie Hebdo attack Reaction to Charlie Hebdo attack A painting of the 'Marianne', the national symbol of the French Republic is placed between candles to commemorate the victims killed in an attack at the Paris offices of the weekly newspaper Charlie Hebdo, in front of the French Embassy in Berlin In pictures: Reaction to Charlie Hebdo attack Reaction to Charlie Hebdo attack Pencils and flowers of condolance are placed at the French embassy at Pariser Platz in Berlin In pictures: Reaction to Charlie Hebdo attack Reaction to Charlie Hebdo attack Mourners hold signs depicting victim's eyes during a rally in support of Charlie Hebdo, a French satirical weekly newspaper that fell victim to an terrorist attack, at Union Square in New York In pictures: Reaction to Charlie Hebdo attack Reaction to Charlie Hebdo attack People hold up placards reading 'I am Charlie' during a gathering in Nice Getty Images In pictures: Reaction to Charlie Hebdo attack Reaction to Charlie Hebdo attack A man lights candles set near the portrait of three of the four cartoonists killed, in Paris Getty Images In pictures: Reaction to Charlie Hebdo attack Reaction to Charlie Hebdo attack A man holds the French national flag tied a black ribbon as he and others gather in Lyon to pay their respects Getty Images In pictures: Reaction to Charlie Hebdo attack Reaction to Charlie Hebdo attack Parisians gather to pay respect for the victims of a terror attack against 'Charlie Hebdo' Getty Images In pictures: Reaction to Charlie Hebdo attack Reaction to Charlie Hebdo attack People gather in front of the 'Club de la presse' in Montpellier, to show their solidarity for the victims of the attack by unknown gunmen on the offices of the satirical weekly, 'Charlie Hebdo' Getty Images In pictures: Reaction to Charlie Hebdo attack Reaction to Charlie Hebdo attack A drawing depicting cartoonist Jean Cabut, left, Charlie Hebdo editor Stephane Charbonnier, center, and cartoonist Georges Wolinski, is placed outside the French Embassy in Berlin, Germany. The message reads 'Victims of their success, R.I.P.' AP In pictures: Reaction to Charlie Hebdo attack Reaction to Charlie Hebdo attack A woman lays a candle during a gathering at the Place de la Republique in Paris Getty Images In pictures: Reaction to Charlie Hebdo attack Reaction to Charlie Hebdo attack People take part in a vigil in Trafalgar Square, London, following the deadly terror attack on French satirical magazine Charlie Hebdo in Paris PA In pictures: Reaction to Charlie Hebdo attack Reaction to Charlie Hebdo attack People light candles forming the name Charlie during a gathering in Strasbourg, eastern France Getty Images In pictures: Reaction to Charlie Hebdo attack Reaction to Charlie Hebdo attack People stand stand in Marseille, southern France, next to a portrait of French cartoonist Georges Wolinksi, killed during an attack by unknown gunmen on the offices of the satirical weekly, 'Charlie Hebdo' Getty Images In pictures: Reaction to Charlie Hebdo attack Reaction to Charlie Hebdo attack People hold placards reading in French 'I am Charlie' during a gathering at the Place de la Republique in Paris Getty Images In pictures: Reaction to Charlie Hebdo attack Reaction to Charlie Hebdo attack A man holds a placard reading 'With all our heart with Charlie Hebdo, Freedom of the press: Our freedom' during a gathering in Marseille, southern France Getty Images In pictures: Reaction to Charlie Hebdo attack Reaction to Charlie Hebdo attack The French and European union flags fly at half-mast at the French Embassy in Washington, DC Getty Images In pictures: Reaction to Charlie Hebdo attack Reaction to Charlie Hebdo attack People gather at the Place Royale in Nantes to show their solidarity for the victims of the attack in Paris Getty Images In pictures: Reaction to Charlie Hebdo attack Reaction to Charlie Hebdo attack Flowers, candles and a sign reading 'I am Charlie' are placed against a wall during a demonstration in Paris AP In pictures: Reaction to Charlie Hebdo attack Reaction to Charlie Hebdo attack Journalism students hold a banner reading in French: 'Journalism students : Solidarity' as they raise pens during a gathering at the Place de la Republique in Paris Getty Images In pictures: Reaction to Charlie Hebdo attack Reaction to Charlie Hebdo attack People gather for a rally in solidarity with the killed Charlie Hebdo employees, in Geneva, Switzerland EPA In pictures: Reaction to Charlie Hebdo attack Reaction to Charlie Hebdo attack A man holds a placard reading: 'Freedom of the press is priceless, fundamentalism, of any kind, will not pass' as others hold up placards reading in French, 'I am Charlie' during a gathering at the Place de la Republique in Paris Getty Images In pictures: Reaction to Charlie Hebdo attack Reaction to Charlie Hebdo attack Journalists raise their press cards as others hold up pens during a gathering at the Place de la Republique, following the terrorist attack on the offices of the satirical weekly, 'Charlie Hebdo' Getty Images In pictures: Reaction to Charlie Hebdo attack Reaction to Charlie Hebdo attack People hold candles at a rally in support of the victims of Wednesday's terrorist attack, at the Place de la Republique in Paris Getty Images In pictures: Reaction to Charlie Hebdo attack Reaction to Charlie Hebdo attack People gather in front of the city hall of Rennes, western France, following the attack in Paris Getty Images

“I'll be meeting with security and intelligence chiefs on Monday morning to once again go through all of those questions and to make sure we do everything we can to in order to ensure we're as well prepared as we can be to deal with this threat.

“It's a threat that has been with us for many years and I believe will be with us for many years to come.”

Speaking to Sky News from a demonstration in support of Paris at Trafalgar Square, the Mayor of London Boris Johnson said: “I’m not interested in this civil liberties stuff. If they’re a threat, I want their emails and calls listened to.”

Mr Johnson called the displays of support in London, Paris and around the world “stunning”. He spoke as the Tricolore was flown from the National Gallery, and its red, white and blue coloured the fountains of Trafalgar Square.

The Lib Dem leader Nick Clegg, who also attended the London demonstration, was criticised by Lord West for blocking the “snooper’s charter” in his capacity as deputy Prime Minister.

“I think we need to make sure that we don't lose powers,” Lord West said. “The Communications Data Bill was there to ensure we kept capabilities we had which are beginning to disappear. I think that needs to go through.

People gather in Trafalgar Square to show their respect to victims of the terrorist attacks in Paris on January 11, 2015 in London, England (Getty)

“I was very irked that it was removed by the deputy prime minister when it had all been agreed across all parties. That needs to be pushed through.”

Labour’s Ed Miliband said he would be “cautious and considered” about calls for more powers for security services.

Mr Miliband told BBC1's Andrew Marr Show: “I think it's right to take a step back and look at this.

“We've got to look at 'Do our intelligence services have the tools they need?' but equally 'Do we have the proper oversight to guarantee the liberties of free citizens?' because, after all, one of the things we want to protect most of all here is our freedoms.”

New Liberal Democrat president Sal Brinton agreed the security services should be able to keep more of an eye on "specific people where they have suspicions".

But she told Sky News' Murnaghan: “If you try and take everybody's phone numbers, everyone they are calling on the phone and also emails, it becomes extremely difficult and I think that's the point where civil liberties rubs up against actual investigation into potential people and we need to be very careful.”