Gordon Brown today unveiled a wide-ranging package of measures to bolster security in public places while attempting to prevent young people being radicalised by violent extremists.
Under the plans set out by the Prime Minister, barriers will be built outside airports, railway stations and ports to protect them from car bomb attacks while new security advice will be sent out to thousands of cinemas, theatres, restaurants and sports stadiums.
At the same time a new unit is being set up bringing together "police and security intelligence and research" to identify individuals at risk of falling under the influence of terrorists.
The move follows the warning last week by MI5 Director General Jonathan Evans that al Qaida was systematically "grooming" children as young as 15 to carry out in attacks in Britain.
In a Commons statement, Mr Brown told MPs: "The objective of al Qaida and related groups is to manipulate political and humanitarian issues in order to gain support for their agenda of murder and violence - and to deliberately maim and kill fellow human beings, including innocent women and children.
"We must not allow anyone to use terrorist activities as a means to divide us or to isolate those belonging to a particular faith or community."
However he was hit by a new row over plans to extend the time terrorist suspects can be held beyond the current 28-day limit after the Security Minister, Admiral Lord West, said that he was not convinced that more time was necessary.
In an interview with the BBC Radio 4 Today programme shortly after 8.10am, Lord West - who carried out the review of security in public places said: "I still need to be fully convinced that we absolutely need more than 28 days."
However, just an hour later, after attending meeting with Mr Brown in No 10, he emerged to issue a hasty U-turn, telling reporters: "My feeling is, yes, we need more than 28 days."
Tory leader David Cameron, who reiterated his party's opposition to any extension of the 28-day limit, said that it appeared that Lord West had been "leant on".
"Won't this episode confirm in some people's minds that, when it comes to this vital and important debate, the Government isn't so much concerned with the evidence as the politics?" he said.
Commenting on Lord West's remarks, Liberal Democrat home affairs spokesman Nick Clegg said: "This is Keystone Cops politics. First the Government wanted 90 days, then 56, then it failed to produce any evidence for a change and the Home Secretary admitted she had no idea how many extra days she wanted.
"Now we have the pitiful spectacle of a minister saying one thing at ten minutes past eight and the exact opposite an hour later after a meeting with the Prime Minister.
"It is alarming that on such a vital issue, which determines the balance of liberty and security in Britain today, the Government appears to have no idea whether it is coming or going."
The approach set out in Mr Brown's statement coupled new security precautions with measures to counter the spread of violent extremism.
He said that in the "most sensitive locations" - including some large railway stations - this would mean additional screening of baggage and passenger searches.
He was however able to offer some respite to frustrated air travellers, with the progressive lifting of the "one-bag" restriction on hand baggage from the new year.
The Prime Minister said that Lord West's review had not identified any "major failures" in the UK's protective security.
However he said that physical defences at the busiest 250 railway stations, together with those at airports, ports, and 100 other "sensitive installations" would be strengthened.
Some 160 counter-terrorism advisers will train civilian staff to identify suspect activity and ensure premises have adequate emergency facilities while architects will be encouraged to "design-in" protective measures into new buildings.
The forthcoming Counter Terrorism Bill will include tougher sentences, new powers of post-sentence monitoring of offenders and additional measures to tackle the financiers of terrorism.
Terrorist trials would be dealt with the appointment of a senior judge to manage all terrorism cases, while a single lead prosecutor in the Crown Prosecution Service would be made responsible for cases relating to incitement to violent extremism.
The new UK Border Agency, announced earlier this year, will be given additional powers of detention while airline liaison officers will be able to cancel visas where there are security concerns.
However a review by Cabinet Secretary Sir Gus O'Donnell rejected opposition demands for police to be included in the agency, which brings together the Home Office's Border and Immigration Agency, Customs and the UK Visas overseas operation.
The security package was accompanied by a series of measures to counter the spread of extremism.
A specialist unit will be set up in the Prison Service to prevent extremists using prison networks to plot future attacks, updated advice will be issued to universities on dealing with extremism on campus while a headteachers' forum will be formed to advise on the protection of children from the extremist message.
Ms Smith will hold talks with the leading internet and global technology companies on blocking online incitement terrorism while measures will also be taken to stop the distribution of extremist literature through public libraries.