The last terrorist bombing on mainland Britain was in August 2001, when a car full of home-made explosives was blown up by the dissident Real IRA in Ealing Broadway, west London.

The attack killed no one and its shock waves have faded to be replaced by tremors of a radically different kind -from the atrocities in Bali in 2002 and in Madrid last year, both of which killed about 200 people.

And behind those reverberations can be heard the rumbles from the suicide jet attacks on the World Trade Centre in September 2001.

Senior police and security service officers are unanimous in their view that the threat to Britain from Islamic fundamentalist terrorism, whether from sophisticated plots by the al-Qa´eda group or Bali- and Madrid-style local extremists inspired by Osama bin Laden, is real and clear.

They have convinced the Government. It gave them the Terrorism Act 2000, expanding their powers to stop, search, arrest and investigate, and allowed the detention without trial of suspected foreign terrorists under the Anti-Terrorism, Crime and Security Act 2001. Charles Clarke has now been convinced and he has replaced David Blunkett´s detention regime with a framework of "control orders".

Unfortunately for anti-terrorist police and agencies such as MI5, MI6 and GCHQ, their persuasive dossiers have largely remained private and they have failed to convince sections of the public - in particular many British Muslims and many lawyers - that the powers and the scale of police activity are proportionate to the threat.

That police activity has been considerable. Since September 11, 2001 to the end of last year, 701 people have been arrested under the Terrorism Act 2000, which requires only "reasonable suspicion" to arrest. Most have come from various branches of the Muslim community - either North Africans, who were the subject of most arrests in the immediate post-September 11 period, and Middle Eastern Muslims, or British-born suspects of Pakistani origin.

However, only 119 of those arrested were charged under the Act. Of those, 45 were also charged with offences under other legislation. A total of 135 others were charged under other legislation, including charges for "terrorist offences that are already covered in general criminal law such as grievous bodily harm and use of firearms or explosives". There have also been a number of fraud cases.

Of the rest, about 60 were transferred to immigration authorities and 351 were released without charge. Only 17 individuals have been convicted of offences under the Terrorism Act and there have been "lesser" convictions, either Irish-related or as a result of membership of proscribed terror groups.

There have been no convictions of alleged Islamic fundamentalist terrorists for the kind of readily understandable "direct" terrorist offences, such as bombings, shootings or possession of explosives and guns, which characterised the years when the Provisional IRA attacked the mainland.

Behind this public activity there is a vast machinery of investigation and intelligence gathering, which has taken officers from MI5 and Scotland Yard to many parts of the world, including Pakistan and Afghanistan, North Africa, and the Middle East. They have pieced together a complex, truly international web of networks, with al-Qa´eda at the top. Below that is a tier of established terrorist groups, in nations such as Egypt that, in addition to fighting their own internal, political battles, have been willing to ally themselves to bin Laden´s cause of a greater, fundamentalist Islamic empire opposed to western, and particularly American, culture.

And then, most worryingly, are young men who have been converted, such as the "shoe bomber" Richard Reid, or those who have been radicalised towards violence by the continued perceived oppression of fellow Muslims. Support networks and terrorist financiers, often involved in credit card fraud, have also been identified. Many of the individual paths can be seen to have crossed, in extremist mosques in the UK and in al-Qa´eda or Taliban training camps in Afghanistan, or in areas of conflict such as Bosnia and Chechnya.

After years of dealing with the IRA, who only ever blew themselves up accidentally, anti-terrorist officers have to plan for suicide bombers - such as the two Britons, from Derby and west London, who went to Israel to sacrifice themselves for the cause.

The warnings given by the IRA, as reckless and inadequate as they often were, have disappeared. No one in Madrid and Bali knew what was coming.

What anti-terrorist forces have so far failed to do, however, is to convey the relevance of this international picture to many Muslim Britons, who see only the low number of convictions and increasing levels of terrorist stops and searches of Asians.

One senior anti-terrorist officer said that they wanted to enlist the help of law-abiding Muslims but "the thing that is missing from large parts of the Muslim community, and certainly those who are most vocal, is any willingness to appreciate the threat.

"It is totally missing. One understands the perception of injustice at home and abroad. But when you deal with these people you have to work your way through the Occupied Territories and Kashmir and then on to the UK. There is no acceptance that there is a threat."

Sir John Stevens, the outgoing Metropolitan Police Commissioner, has referred to successes by police and MI5 in thwarting at least eight plots or attacks. These are thought to include the operation in January 2003 in which tanks were deployed at Heathrow because of a suspected plot to shoot down an airliner.

Sir John said he could not give details of the most important investigations because they were before the courts. (© Copyright of Telegraph Group Limited 2004. 01/27/05)