In a vivid documentary called The Ministry of Truth, Richard Symons recently argued it is unacceptable that MPs can’t be sued or prosecuted for telling lies in the course of their job. He gained the support of Adam Price MP to introduce a Bill making it a criminal offence for a politician to “recklessly or with intent to deceive” tell a lie about matters of government. A politician convicted of this offence would be disqualified from standing as representative of the people.

Although the UK is currently well-stocked for laws – we already have over 500,000 rules – there is none at the moment about an MP’s obligation to be honest. It would be an eminently sensible law.

There is no general law against telling lies but there are many laws designed to condemn telling lies in particular situations. So, telling people at work that you are the messiah is merely silly but telling a lie in court under oath is a specific offence: perjury. Similarly, lying in the context of trade descriptions, Inland Revenue returns, and applications for state benefits, are all offences. If we agree that all those circumstances are so serious that telling lies in them is a crime, it makes sense to subject politicians to the same law. Why should second hand car sales be more tightly regulated than the peddling of political propositions?

History helps explain the current situation, and how things might change. In the 17th century, members of Parliament took power from the Crown. One of the results of that fight was that Parliament became entirely self-regulating. It is a good guardian of public interests, but, as Juvenal asked (about 220 AD), “quis custodiet ipsos custodes?” — who is to guard the guardians themselves? In the light of many modern cases of fraudulent politicians, there is an arguable need for their self-regulation to be replaced by a special law.

The obligation for politicians to tell the truth could be put on as clear a legal footing as it is for other responsible people. The Companies Act 2006 contains various offences, such as fraudulent trading, to control people with corporate responsibility. In broadcasting, section 144 of the Broadcasting Act 1996 creates a crime, punishable by imprisonment and fine, of giving false information in support of an application for a licence to broadcast. Would anyone today say that, unlike those who apply to become broadcasters, those who go into politics are naturally so honest and impeccable that they don’t need to be governed by law about truth?

Honesty is a difficult concept because, as Algernon tells Jack in The Importance of Being Earnest, "the truth is rarely pure and never simple". But the law gets on with things using a good measure of common sense. In criminal law, there are over 200,000 cases each year in which the outcome hinges on whether the defendant acted dishonestly. The standard to be applied is that of "reasonable and honest people". Ordinary people judge thousands of such cases as jurors. If ordinary people are good enough to empower politicians through the ballot box, they’re good enough to judge them in a court.

Jack Straw says that such a law is unnecessary because we already have enough checks. He says politicians would be crazy to lie as they’d be easily caught and the social retribution (they’d lose their jobs) is enough. But this misses the point that you’re likely to get much more lying in circumstances where there is no specific law against it than you would where lying is illegal. It also ignores the need to stamp with particular disapproval lies told by politicians concerning the body politic. In 1727 a court upheld the view of the Attorney-General who had said “I do not insist that every immoral act is indictable, such as telling a lie . . . but if it is destructive of morality in general, if it does, or may, affect all the King's subjects, it then is an offence of a public nature."

It’s hardly surprising that not much more than a third of the electorate votes for our law-makers these days. A recent MSN poll showed that 96 per cent of 13,000 respondents don’t trust politicians. Disenchanted citizens appear to be accepting the opinion of Groucho Marx that politics is “the art of looking for trouble, finding it everywhere, diagnosing it incorrectly, and applying the wrong remedy”.

The new Bill would make politicians as cautious in what they say as witnesses are in court. In 1891, Mr Justice Hawkins said that courts couldn’t “weigh in golden scales the acts of men hot in their political excitement.” Today, though, allegations of misleading the public could become justiciable (triable in a legal process). That would no more mean that any casual comment during a radio interview would end up in court than the Theft Act means that any pencil swiped from work puts someone behind bars. But the law would clarify that the status of politician is not a licence to lie.

Professor Gary Slapper is Director of the Centre for Law at The Open University

Times Recommends

• BGC 'set aside £40m to lure Tullett brokers'
• Legal aid review to ensure value
• Fears as 21 magistrates' courts face closure