None of the revelations about the July 7 bombings should come as a surprise. Past terrorism trials have shown that British Islamist terrorists are a band of fanatics who are frequently known to one another and have sometimes trained or been indoctrinated together.

Some are skilled in anti-surveillance techniques and their numbers are such that it is impossible for counter-terrorist agencies to keep track of every one of them.

If this causes shock that is because there is a lack of understanding in Britain of the nature and scale of the terrorist threat.

That absence is caused largely because discussion of terrorism — whether conducted in the media or the mosque, the Commons or the courts — is characterised by complacency, stymied by denial or cloaked in secrecy.

Men like Mohammed Sidique Khan and Omar Khyam were part of a network of Islamists who carried their religious radicalism into terrorism. Trace back their movements, their phone calls and their associates and you will link them all. The network they were part of is still best called by the name al-Qaeda.

The tightly controlled structure that existed before September 11, 2001 was damaged by the US-led invasion of Afghanistan. But al-Qaeda has rebuilt itself in the tribal areas of Pakistan and is not it in the state of disarray that many intelligence agencies claimed a year or two ago. The head of Scotland Yard's Counter-Terrorism Command said only last week that "the hand of core al-Qaeda" had guided a series of terrorist plots against the UK.

A common pattern of movements exists in 7/7 and the Operation Crevice case.The terrorists travelled to and from Pakistan, where al-Qaeda’s leaders are based. All their plots were conceived of, planned in and directed from Pakistan.

It is relatively easy for terrorists and jihadis to blend in with the 400,000 people who visit Pakistan from Britain every year and stay, on average, for 41 days.

Khan spent three months in Pakistan from December 2004. He was programmed to become a “martyr”, taught how to make bombs and sent home to commit murder on the Tube.

Pakistan’s role might be likened to that of the Irish Republic at the height of the IRA campaign — offering a relatively safe haven for terrorist activity.

And, as with the IRA, there is a sizeable population within the borders of the UK which feels beleaguered, persecuted and more hostile to the forces of law and order than it is to the terrorists.

Among that population there are active al-Qaeda supporters and recruiters. Once they were very visible in the form of Abu Hamza and the Finsbury Park Mosque or the al-Muhajiroun movement.

Those figureheads are in exile or in jail, but their successors are still busy raising money, indoctrinating and talent-spotting the best (or the most gullible) for final training in Pakistan.

Two thousand people are estimated to be involved in al-Qaeda activity in Britain. Khan had connections and associations dating back at least to 1999 (long before 9/11 or the invasion of Iraq).

There is no doubt that mistakes were made by MI5 and others which allowed him to remain free to commit the outrages of 7/7. Equally there is little doubt that, despite greater anti-terrorist resources and tougher legislation, another bomber will slip through the net. Al-Qaeda will strike again.

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