It is not children who should be seen and not heard. It is the police. As Sir Ian Blair’s comments yesterday demonstrated, however, they are too often heard — just as they are rarely seen.

The Commissioner of the Metropolitan Police entered the election campaign with his view that new legislation is needed to criminalise “acts preparatory to terrorism” and “very loose-knit conspiracies”, such as those around Kamel Bourgass and his acquitted associates. Sir Ian is not merely wrong — he has also come close to demonstrating that he is not up to his job.

The implication behind Sir Ian’s words is that, if the law had been stronger, Bourgass’s fellow defendants would now be in jail. Sir Ian appears to be unaware of the existence of the Terrorism Act 2000, which deals specifically with the “acts preparatory to terrorism” and “very loose-knit conspiracies”.

Take Section 57 (1): A person commits an offence if he possesses an article in circumstances which give rise to a reasonable suspicion that his possession is for a purpose connected with the commission, preparation or instigation of an act of terrorism.

Note the words “preparation” and “instigation”. The legislation covers precisely the circumstances of Bourgass and his fellow defendants — when no act has yet been committed, but is being planned.

The police and security services are apparently still convinced that the defendants were preparing a major attack. That they were acquitted had nothing to do with the absence of appropriate legislation. The police claim that the jury was not allowed to hear much important evidence.

The idea that the Commissioner of the Metropolitan Police does not know the details of existing anti-terror legislation is worrying enough.

What is still worse is that he does not seem to understand the function of the police force. It is Parliament’s job to decide on the law, not the police’s. Sir Ian’s job is to enforce it — a job at which, as many victims of crime will attest, he has so far appeared clueless. He demonstrated his priorities with almost his first act as commissioner: to dig into his limited budget to change the typeface on his force’s motto, which “discriminated against short-sighted people”, to a simpler font.

Tough on italic fonts; ignorant of the law; happy to shoot his mouth off. It has hardly been an auspicious start to Sir Ian’s tenure.