Hardly a week has gone by this year without a warning about al-Qaeda, a series of police raids or a court hearing for terrorism suspects.
The police and the intelligence services have been working flat out - the more arrests they make, the more information there is to process.
The more information they have, the more arrests they need to make...
Their first major task came in January with the discovery of traces of ricin at a flat in north London.
Ricin is a toxic material extracted from the beans of the castor oil plant. It can be fatal when inhaled, ingested or - most dangerously - injected.
Later that month, Richard Reid from Britain was jailed in the US for attempting to set fire to explosives hidden in his shoe on board an American Airlines flight from Paris to Miami.
During his trial he expressed no regret, pleading guilty and saying: "I pledge to Osama Bin Laden. I'm an enemy of your country."
'Real and present' threat
In April, two men from Leicester were found guilty of raising funds for al-Qaeda - the first and most significant convictions under British anti-terrorism laws since the 11 September attacks on America.
The pair - Baghdad Meziane and Brahim Benmerzouga - were each jailed for 11 years, but have been granted leave to appeal.
The threat from terrorists was underlined by the prime minister, who warned of the "real and present" threat posed to global security by international terrorists and said they were close to achieving nuclear capability.
It was a theme that was echoed during the year by other political leaders, senior police and law enforcement officers and those involved in civil contingency planning.
'A matter of time'
But of all the public statements about the terrorist threat, most striking was the assessment given by MI5 director general Eliza Manningham-Buller.
Unlike her predecessor who rarely made speeches, Ms Manningham-Buller appeared in public twice within four months.
In June, she said it was "only a matter of time" before terrorists launched a biological, chemical or nuclear attack on a Western city.
British interests have been targeted abroad
She said renegade scientists had provided al-Qaeda with the information needed to launch such an attack. It might take the form of a radiological strike - sometimes known as a "dirty bomb".
In October, she spoke about her "fear" that the threat from Islamist terrorism would remain for a long time to come.
She offered an intriguing insight into the workings of al-Qaeda, describing the group as "sophisticated and particularly resilient".
Networks of individuals sympathetic to their aims were able to blend into British society - living normal, routine lives until called upon for specific tasks.
But it wasn't just words. On the ground, there were clear signs of the increased threat, as the authorities began to update their plans in the event of terrorist strike.
A simulated chemical attack was staged in central London to assess the ability of the emergency services to respond.
Extra police have patrolled certain high-profile targets
Concrete blocks were placed outside the Houses of Parliament - to deter suicide bombers.
And in February, light tanks and extra police were deployed at Heathrow Airport in response to intelligence indicating that terrorists were plotting to shoot down a plane.
But although the UK has now been placed on its second highest level of terror alert - classed as "severe general" - the public have been told not to be alarmed.
Stay vigilant, don't be complacent, and carry on as normal is the message.