Image copyright PA Image caption Alistair Carmichael is facing calls to resign

Spare a thought for poor Alistair Carmichael. Not only does he cut a lonely figure in Parliament these days as the Liberal Democrats' last surviving MP in Scotland, but he's also under investigation for breaking the MPs' code of conduct, which is a fancy way of saying lying.

This week a parliamentary standards watchdog launched a formal inquiry into Mr Carmichael, until recently the minister in Westminster responsible for Scottish matters.

In short he's now admitted he had agreed to the leak of a document aimed at damaging the Scottish National Party during the recent general election campaign, although at the time he denied it.

Not a very successful leak, it has to be said, given the outcome of the election - nor, to be fair, one of the biggest whoppers in the history of political lies.

Code of Conduct

The Parliamentary Standards Commissioner will investigate Mr Carmichael's actions under three sections of the MPs' code of conduct. These are:

Section 10: Members shall base their conduct on a consideration of the public interest, avoid conflict between personal interest and the public interest and resolve any conflict between the two, at once, and in favour of the public interest.

Section 14: Information which members receive in confidence in the course of their parliamentary duties should be used only in connection with those duties. Such information must never be used for the purpose of financial gain.

Section 16: Members shall never undertake any action which would cause significant damage to the reputation and integrity of the House of Commons as a whole, or of its members generally.

I mean alongside President Richard Nixon saying he didn't know anything about Watergate, you have the former Soviet leader Nikita Khrushchev denying the USSR was sending offensive weapons to Cuba.

Then there's Bill Clinton saying, ahem, he "did not have sexual relations with that woman" (Monica Lewinsky) or yes, the Greeks telling those poor Trojans the horse was definitely a let's-kiss-and-make-up present, well Alistair's is a teeny, tiny fib.

Image copyright Getty Images Image caption Bill Clinton: "I did not have sexual relations with that woman"

But is lying by political leaders or the state ever justified?

Well, this probably isn't the place for some long philosophical musing on such a profound question of ethics and politics. But the argument has been made in the past and will no doubt be made in the future that it is OK to lie - or rather to have secrets - when security is at stake. Or put another way, it was all right for the Allies not to let the Germans know which beaches they would be using on D-Day at the end of World War Two.

Of course, it's one thing to lie or to deceive your enemies in war or hostile foreign states, but what about your own citizens? And can you lie just for your own political advantage?

Right or wrong, grave or otherwise, there's certainly no shortage of such behaviour, according to one of those Liberal Democrat MPs culled in last month's election.

In a recent interview with the BBC, Malcolm Bruce said Parliament would be empty if politicians were punished for telling lies. But what place of work wouldn't be, you might ask, under such a rigid code.

Image copyright AP Image caption Lenin is reported to have said: "A lie told often enough becomes the truth"

So what about us voters? Is any of this our fault, do we get the politicians we deserve?

Intriguingly I came across an American psychologist, Ron Riggio, who has suggested it is sort of our fault, in that we humans as a whole are a rather trusting bunch who want to believe what we've been told.

Less charitably, it's also said that politicians can be sparing with the truth, because they rightly judge that we don't want to hear it. So let's not tell the voters about those spending cuts or that noisy new airport as they'll only get upset.

If I've got you mulling over the issue of truth and politics, let me leave you with two further thoughts, the first from the Soviet leader Vladimir Lenin, who is said to have remarked that "a lie told often enough becomes the truth".

The second is from the great American writer Mark Twain, who wrote: "If you tell the truth you don't have to remember anything."

Personally I've always been more of a Huck Finn fan than a Leninist.