Seven terrorist attacks have been thwarted in the last six months David Cameron has revealed as he announced plans to recruit of nearly 2,000 new spies.
He warned that the deadly terrorist attacks that hit Paris on Friday night, killing 129 people, "could happen here" and Britain faced a continued threat by Isis.
The Prime Minister responded to the Paris attacks by announcing a 15 per cent increase in the security and intelligence staff at M15, MI6 and GCHQ and doubling the spending on security at airports across the UK.
He said the terror spree in the French capital "was the sort of thing we warned about" in planning with the security services but such atrocities meant "you have to go right back to the drawing board" to work out what more steps needed to be taken.
He also hinted that the Government could speed up the passage of the Investigatory Powers Bill, which will give the security agencies new spying powers.
"We should look at the timetable; we do need to take Parliament and people with us,” Mr Cameron told the Today programme.
The world mourns Paris attacks - in pictures
The world mourns Paris attacks - in pictures
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Members of the public gather to lay flowers and light candles at La Belle Equipe restaraunt on Rue de Charonne in Paris
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People lay a memorial to honour victims of the Paris terror attacks at Federation Square in Melbourne, Australia
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Soccer fans display the colors of the French flag in response to the deadly terrorist attack in Paris, France before the soccer match between the New York Cosmos' and the Ottawa Fury for the North American Soccer League championship at Hofstra University in Hempstead, New York, USA
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Pakistani Civil society activists shout slogans during a protest against Isis militants near the French consulate for the victims of the 13 November Paris attacks in Karachi, Pakistan
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People gather and view messages written on the ground at Place de la Republique in Paris
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French flags and a note reading "We will not let you spoil our children's lives" at the site of the attack at the Cafe Belle Equipe on rue de Charonne in the 11th district, in Paris
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A rose is placed beside a bullet hole at La Belle Equipe restaraunt on Rue de Charonne following the terrorist attack in Paris. As France observes three days of national mourning members of the public continue to pay tribute to the victims of deadly attacks
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People gather for a national service for the victims of the terror attack at Notre Dame cathedral in Paris
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Bono and band members of U2 pay their respects and place flowers on the pavement near the scene of yesterday's Bataclan Theatre terrorist attack in Paris
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A man kneels as he pays tribute to victims at Place de la Republique near the deadly attack sites in Paris
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Tributes to the victims at the Place de la Republique square in Paris
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An electronic billboard on a canal show solidarity with Paris in Milan
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People lay down flowers and light candles to tribute victims of Friday's attacks in Paris as the Brandenburg gate is illuminated in blue, white and red in the colors of the French flag, in Berlin
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A man leaves flowers as a tribute following the deadly attacks in Paris, outside the French consulate in Istanbul
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People take pictures of flowers placed in bullet holes in the window of a Japanese restaurant next to the cafe 'La Belle Equipe'
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People gather at a makeshift memorial next to the Bataclan theatre in Paris on November 14, 2015,
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A woman carrying flowers cries in front of the Carillon cafe and the Petit Cambodge restaurant in Paris
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People gather in front of flowers that were laid outside the French embassy in Rome
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People react near the cafe 'La Belle Equipe' at the Rue de Charonne
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A young girl places a candle in front of the Carillon cafe in Paris
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Flowers placed outside the cafe 'La Belle Equipe' at the Rue de Charonne in Paris, the scene for one of the attacks
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A woman is comforted by others outside the Carillon cafe and the Petit Cambodge restaurant in Paris
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The Brandenbourg Gate featuring French national colors is pictured in Berlin, on November 14, 2015 a day after deadly attacks in Paris
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Flowers are laid in front of the French embassy in Rome
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A candle is lit next to flowers outside the French Embassy in Berlin
Explaining the extent of the threat posed by Isis, Mr Cameron said: “We have been aware of these cells operating in Syria that are radicalising people in our own countries, potentially sending people back to carry out attacks.
"Our security and intelligence services have stopped something like seven attacks in the last six months, albeit attacks planned on a smaller scale."
President Francois Hollande declared Friday's attacks in Paris as an "act of war". Mr Cameron, asked whether Britain was "at war" with Isis, stopped short of using the same words but said the UK stood in "total solidarity" with France and would do "everything we can" to defeat the "disease of Islamist extremism".
The increase in national security provisions, announced on Monday morning, are part of the five-year defence and security review, which will be unveiled in full next week.
Announcing the boost in spying staff, which will see the total number working at MI5, MI6 and GCHQ increase from around 12,700 to 14,600, Mr Cameron said: "Our intelligence agencies work round the clock behind the scenes and as the threat has grown so they too have risen to the challenge.
"Much of what they do cannot be seen by us or talked about but their courageous and determined efforts allow us to go about our daily life.
“This is a generational struggle that demands we provide more manpower to combat those who would destroy us and our values."
The attacks in Paris proved why Britain's security agencies needed the powers set out in the Investigatory Powers Bill so urgently, Mr Cameron added.
He said: "This disease of Islamist extremist violence, this perversion of the religion, of the religion of Islam that is being carried out by this minority of a minority as it were, this is a challenge we are going to have to face with everything we have got.
"Now that means investing in the hard power of our military, because that can be important, it means boosting our counter-terrorism capabilities, and we should think absolutely, the bill we are taking through parliament to strengthen our capabilities to intercept the communications of terrorists is a vital part of this fight...
"Remember this is about maintaining our capabilities and putting everything on a very clear statutory footing."
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