It is reassuring to learn that Richard Thomas, the information commissioner, is fighting on the side of the angels against the “surveillance society”. These are the state agencies that hold a growing body of personal and possibly inaccurate information on even the most inoffensive members of the public. It is comforting, too, to hear him lambast the high street banks, as he did in an interview yesterday, for leaving their customers’ financial records in bin bags on the pavement, vulnerable to identity thieves. One can but applaud his horror that a father was on police records as a suspected paedophile for five years after a dinner lady overheard his daughter say, “My dad bonked me last night”, when she meant that he had tapped her on the head with an inflatable hammer.

Mr Thomas, one could think, is a man determined to expose malpractice and to cut the mighty down to size. Much less cheering, however, are his views on a matter of overwhelming importance that he did not talk about in his interview: the role of the press in protecting the public by exposing the abuses of the powerful. Newspapers had already been doing this for centuries when he took up his post four years ago. This duty of the media is vital in the struggle to maintain an open society. Yet Mr Thomas would send reporters to prison for fulfilling it. His record in opening up the public sector to scrutiny as enforcer of the Freedom of Information Act — the other hat that he wears in a masterful piece of Whitehall doublethink — is disappointing. And his position in data protection is entirely on the side of those with something to hide.

In a little noticed report to parliament this year, he highlighted how people’s personal details — “who they are, where they live, who their friends and family are, how they run their lives” — now form part of a trade in “confidential personal information” that was made illegal under the Data Protection Act 1998. He says that “much more illegal activity lies hidden under the surface”. This can consist of obtaining “ someone’s current address, details of car ownership, an ex-directory telephone number or records of calls made”. The commissioner states that he “will not hesitate to prosecute journalists identified in previous investigations who continue to commit these offences”. In saying this he is echoing the Department for Constitutional Affairs, which has responsibility for the law. If he and the department have their way, they calculate that one journalist a year could go to prison for breaches of the Data Protection Act. The maximum penalty is two years.

To a Whitehall lawyer such as Mr Thomas, appointed to his post by No 10, this might seem entirely just: the law is broken, punishment is due. To a newspaper or television company considering an investigation into political or commercial chicanery, it is the criminalisation of free speech. “Where someone lives, who they are, who their friends and family may be” is hardly confidential information. It is common currency that is easily discovered by talking to neighbours, looking at the electoral register or searching the Land Registry, as anyone is entitled to do. To propose imprisonment for reporters — and insurers, solicitors and private investigators — who obtain such details would be laughable if it were not so sinister.

It is equally true that journalists are not above the law and newspapers can already be fined an unlimited amount for breaches of the Data Protection Act. But the threat of imprisonment will curtail free speech even if the journalist can argue a defence of public interest, something that is a notoriously prone to different interpretations by different judges. Mr Thomas is complicit in placing another brick in the wall that the state is building to protect itself from unwanted scrutiny. This newpaper’s front page story today on cash for honours is precisely the sort of investigation that political parties would prefer not to happen. Mr Thomas is doing his bit to help them.