The level of threat from terrorism has increased, the government says
The government's plan to train 60,000 workers to look out for potential terror attacks is "flawed", the Conservatives have said.
Shadow home secretary Chris Grayling said this would amount to a "voluntary three-hour seminar", less than half the length of a cycling proficiency course.
The programme outlined by the government was "dispiriting", he added.
Defending her strategy to MPs, Home Secretary Jacqui Smith said it was "comprehensive and wide-ranging".
It includes training 60,000 workers in vigilance for terrorist activity and what to do in an attack, among them shop and hotel workers.
Ms Smith said the updated counter-terror strategy would also include:
- Tackling anti-democratic extremist voices in the community
- Supporting mainstream pro-democratic Muslim voices
- Preventing access to internet information on setting up attacks
- More funding for anti-terror police and intelligence resources
The strategy document talks about the need to "challenge those who reject the rights to which we are committed, scorn the institutions and values of our parliamentary democracy, dismiss the rule of law and promote intolerance".
Ms Smith said the recent killings of two soldiers and a policeman in Northern Ireland had been a "chilling reminder that terrorism has not left our shores".
But the threat posed by al-Qaeda was of a "different scale and nature", which was "always evolving".
An attack was "highly likely and could happen, without warning, at any time".
Ms Smith added: "The vital work to counter terrorism cannot be done by government, police and intelligence agencies working alone."
But Mr Grayling said not enough action was being taken against extremists.
The training scheme had not been "what we were promised" previously by the government.
It was, rather, a "voluntary, three-hour seminar, and that includes the coffee break".
Mr Grayling added: "This is less than half the length devoted to a cycling proficiency course...
"The government's strategy is not perfect... We will continue to push for change in the areas where it's flawed."
Liberal Democrat home affairs spokesman Chris Huhne raised concerns about the methods used to combat terrorism, including holding suspects without charge for up to 28 days.
People going about their daily lives such as trainspotters and night fishermen had been arrested by "overzealous" police officers citing security issues, he said.
He added: "Though the threat is severe, our response must always be measured and proportionate.
"We must never become what we are fighting, for that way lies the loss of the moral high ground and the esteem of the very people we need to provide intelligence and witnesses."
Labour MP Keith Vaz, chairman of the Commons home affairs select committee, said: "It is vitally important that we continue to work with the private sector to ensure that they put in place the necessary security arrangements in our major hotels and our major tourist destinations.
"These are places that are going to be targeted by terrorists and we must prepare for that."
The government paper - called Contest Two - will update the Contest strategy developed by the Home Office in 2003, which was later detailed in the Countering International Terrorism document released in 2006.
By 2011, Britain will be spending £3.5bn a year on counter-terrorism, the Ms Smith said, while the number of police working on counter-terrorism had risen to 3,000, from 1,700 in 2003.