So was there or was there not a plot to bring down airliners? I know what I think. The jury agreed that some of those on trial wanted to commit murder, but couldn’t agree, despite strong evidence, that the targets were airliners.

They have not rejected the possibility, and while the lawyers pick the bones out of the messy end to this trial we can still be satisfied with what the “surveillance society” has achieved. Many innocent people, targets of a group of homicidal terrorists, are safely at work, at home or on holiday with their families.

But the terrorists didn’t end up in prison by accident. They didn’t suffer a pang of conscience, give themselves up to the police and throw themselves on the mercy of the courts. They were hunted down by the most sophisticated counter-terrorist bodies in the world, and convicted by one of the oldest judicial systems.

On the evening of August 9, 2006, I was told that a man connected to the British terrorists had been arrested in Pakistan. This was not good news. We were at a critical point in building our case against them. If they got to hear that he had been arrested they might destroy evidence and scatter to the four winds. More worrying still, if they were tipped off to the arrest they might panic and mount a desperate attack.

At Scotland Yard we decided, in a matter of minutes, that Operation Overt had to be brought to an end and all 20 suspects arrested immediately.

Detectives rushed to the Yard from all quarters, were briefed and sent to make their arrests. In the operations room, as the night wore on, the number of red dots against suspects’ names, used to signify they had been arrested, steadily grew. By morning, all were in the cells.

The convictions secured yesterday are another important landmark in a series of terrorist cases stretching back to 2004. The common denominator in each is Pakistan, with British terrorists travelling there for training and tasking. Dig deep enough and you will find connections between them all: some clear, some opaque and some assumed by virtue of coincidence of travel patterns. For instance, it is a fact that some members of several of these plots were in Pakistan at the same time in 2004.

Are there more plots directed at the UK from this source? I would be amazed if there were not. Al-Qaeda have proved to be incredibly resilient. Time and again they have been attacked, suffered losses, both on the battlefield and in the courtroom, and yet still they keep coming. Now is not the time to take off the pressure.

We have what is probably the most effective counter-terrorist machinery in the world. The organisations involved have been at full stretch for years, and despite the gainsayers, the legal and ethical standards of the counter-terrorist effort are incredibly high - the British public demands and deserves no less.

They also deserve a better quality debate about the relationship between individual liberties and collective security.

Take this case. To save the lives of the innocent and convict the would-be killers we used all the tools in the security armoury. Deeply intrusive surveillance, informants, CCTV, DNA, telephone call data and so on. This was not about collecting information for its own sake - it was to secure evidence to put before a court.

Some critics fail to understand that sophisticated, modern evidence gathering has allowed the most complex terrorist conspiracies to be tried in our criminal courts in front of a jury. No need for military commissions or the juryless Diplock courts of Northern Ireland.

The series of terrorist convictions in recent years has been a victory for the rule of law and sends out a strong, positive signal to all communities. But it couldn’t have happened if things that used to be buried deep in the world of intelligence were not now brought blinking into the light of the courtroom.

And what if we had failed? What if the prosecution case was right, and half a dozen American airliners were to be brought down by British terrorists, operating from Britain and in effect using the UK as a launch pad for an attack on the United States? What would have happened to the UK and indeed the global economy? What would the impact have been on UK/US relations? What about the pressure it would have placed on Muslims in the UK? A very senior politician, at the time of the arrests, told me he thought it could have led to a breakdown in the community cohesion that had survived the attacks in 2005.

So let’s remember the benefits of the “surveillance society”. We should draw satisfaction that due to terrorist convictions in our courts, thousands of people are alive today because those who wanted to kill them could be bugged and burgled - within the Rule of Law and for the common good.

Peter Clarke retired as head of Counter Terrorism Command in 2008 and led the liquid bomb plot inquiry

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