Andreas Whittam Smith: Why don't I feel safer after the east London raid?

I hope we have got the Security Service, the Metropolitan Police and the Special Branch that we need in these dangerous times. The massive raid on an east London house early last Friday morning, in the expectation of finding weapon-making facilities using toxic chemical or biological agents, does raise some doubts.

For the exercise was a curious mixture of precaution and "anything-goes". Anti-terrorism police wore protective suits. Some carried gas masks. Even an air-exclusion zone was established above two humble residences in Forest Gate.

Yet, although it was believed that an explosive device able to spread poison over a wide area might be found, there was no evacuation. The next day the parents of the two young men who were arrested were able to fly to Mauritius on holiday as if nothing had happened, their house still being searched by the police. Such inconsistency plays into a growing concern that perhaps these illustrious institutions are struggling to find a balanced response to the threat of outrages in the capital city and elsewhere.

At the heart of the raid was a small terrace house, a single family home that connected with an adjacent property. It contained one family: mother and father and their two sons, both in the early twenties, and their two daughters. To subdue this lot, Scotland Yard needed a force of some 250 officers. So many police to arrest two young men appears just as over-the-top as the same force's use recently of 78 officers to remove 120ft of anti-war hoarding in Parliament Square. Can it be that the Metropolitan Police has more staff than it really requires? Then there was the shooting of one of the two men who were arrested. It is unclear how this happened except that the Metropolitan Police seem to be subject to Murphy's Law: "If anything can go wrong, it will."

According to a Sunday newspaper a police weapon with its safety catch off was inadvertently fired during a struggle. Unfortunately this incident brings back memories of the shooting dead by police of an innocent Brazilian, Jean Charles de Menezes, in the aftermath of the London Tube bombings.

At the time of writing, nothing has been found to justify the raid. This is not in itself a reason for criticism. Anti-terrorism work differs from normal police activities in that it is largely concerned with the prevention of crime. It is involved with "who might do what?" rather than with "who did it?" It is trying to prove an intention. This is intrinsically difficult and mistakes are bound to be made. What appears to have happened is that MI5 was told last month that two Muslim men, already well known to the security services, were preparing a device. The informant, who knew the suspects, is said to have overheard an incriminating conversation.

If nothing is found, though, this story will also ring some bells. Wasn't the whole Iraq disaster caused by faulty intelligence that came from informers who were playing games? It is very difficult for outsiders to gauge the strength of the terrorist threat. I have myself heard the impressive director-general of M15, Dame Eliza Manningham-Buller, emphasise the terrifying nature of what the security services confront.

Now it is said (not by Dame Eliza) that hundreds of men and women leading ordinary lives in the suburbs form a "silent 1,200 strong army of terrorists". Between them the mysterious 1,200 have some "20 major plots" under way that they hope will bring death and destruction to Britain. I am afraid this sounds like complete twaddle to me.

At the same time as Scotland Yard was dispatching 250 officers to east London, the Canadian police carried out a security operation. They arrested 17 men and five youths in Toronto, all Canadian citizens, and charged them with plotting to attack targets in southern Ontario with crude bombs made of ammonium nitrate, a fertiliser which combines with fuel oil to make an explosive.

The only trouble is the delivery of three tons of ammonium nitrate to the group turns out to have been part of a sting operation. Security services investigators were themselves controlling the sale and transport of the massive amount of fertiliser, a key component in creating explosives. When the deal was done, the Canadian police moved in to make the arrests.

In the British case, the police make their raid and have so far found nothing. In the Canadian case the police similarly carry out arrests and find what they were looking for - but only because they put it there themselves!

None of this makes me feel any safer. Paradoxically, I might have more confidence in the security services if they didn't try so hard. More than anything I wonder whether they have retained a sense of proportion.