You don't have to be a fan of political comedy series The Thick of It to work out how Alistair Carmichael, the former LibDem Scottish Secretary, got himself into such a big fat mess.

Imagine his office in the midst of an election campaign when the opposing SNP looked set for a landslide. With the abyss of electoral defeat fast approaching, someone recalls a memo of a conversation between Nicola Sturgeon and the French ambassador back in February. It reports Sturgeon saying she'd prefer David Cameron to remain prime minister. Should they leak it?

In the wake of Sturgeon's star performance at the first leaders' debate, Carmichael said yes.

You can understand his reasoning. If Sturgeon could be shown to be secretly backing Cameron while publicly courting Miliband to "lock out" the Tories - she would be damaged. She'd look hypocritical. During the campaign, every time she said the word "Tory" it sounded pejorative.

Carmichael could be forgiven for thinking the memo might turn the opinion polls, something that nothing else that had been thrown at the SNP by their opponents had managed to do. Sturgeon's credibility would be ruined. The electorate would feel duped.

Perhaps, Carmichael must have thought, this leak could be the butterfly that clapped its wings and triggered a series of events leading to a tsunami that would wash away the SNP.

So he authorised the leak. It was a harsh decision; ruthless even, the action of a general in battle. But politics is a rough game, often visceral and he was a seasoned player.

He must have momentarily scented success when headlines about the memo were speedily followed by Ed Miliband stampeding to publicly castigate the First Minister. But the triumphalism was short-lived.

Sturgeon tweeted a flat denial. Then came the clincher; the French backed her version of events. And the smear fell flat. Worse, for Carmichael, it led to a leaks inquiry.

All this might have been survivable if Alistair Carmichael had owned up immediately. He could have claimed he believed the memo was correct; that the leak was in the public interest, information that the voting public should know.

Like all politicians he is practised in navigating a passage between an actual lie and the truth. He could have thrown himself on the mercy of his electorate. It would have been another gamble but it would have had the merit of being the most honourable way out of a dishonourable hole.

He chose another way. First he covered up and then he lied. He stated repeatedly, on television, that he knew of the memo only when a journalist rang him about it.

The findings of the leak inquiry, announced last week, have been his undoing. As a result he has apologised to Nicola Sturgeon and to the French ambassador. He has also declined his ministerial severance payment of about £17,000.

So is that punishment enough? I'm afraid I don't think so.

One of the reasons is that in 2012 the same Alistair Carmichael wrote a letter from Westminster for The Shetland Times saying: "The right of freedom of speech is a fundamental one but it does bring a responsibility with it to tell the truth. The right to smear an opponent is not one we should be defending."

Doesn't that condemn him out of his own mouth?

It pains me to think that his situation is non-negotiable. But isn't it?

Carmichael is the only LibDem MP left in Scotland. In my view that is another reason why he can't cling on. The Liberal Democrats have just paid the costly electoral price of their former leader Nick Clegg going back on his word over tuition fees. The last thing it needs is a solitary MP whose trustworthiness is in question for the next five years.

Carmichael's majority in Orkney and Shetland is a slim 817 (down from 10,000). Now I think he's going to have to test it again.

The Scottish Liberal Democrat executive at the weekend agreed no disciplinary action would be taken against him. His leader Willie Rennie pointed out that Carmichael has already expressed regret. Rennie said the MP deserves a second chance.

I'm a great believer in second chances. I've needed a few. Far be it from me to deny anyone the possibility of forgiveness and making good.

But they don't necessarily get to do it while in the same position.

When television star Jeremy Clarkson fuelled by anger and entitlement, punched a colleague, he forfeited his job. The BBC made the decision with considerable pain, given the value of Top Gear and the size of its global audience.

When a senior politician commits so serious an error of judgement , surely he needs to do more than voluntarily forfeit a severance payment.

Shouldn't the manner and degree of the reparation required be decided by a higher authority than himself?

That higher authority can't even be his party executive or party leader. His fate has to be decided by the people who have given him his job; by the electorate. That must be the most appropriate course of action since he was able to present himself to the voters of the Northern Isles as a more honourable man than has turned out to be the case.

Now, less than three weeks after the polls closed, enough of them might have reason to believe they had voted for someone else.

There should be a re-run of the poll.

Carmichael himself must agree. He supported the 2009 Early Day Motion bill on the right of voters to recall their MP in certain circumstances.

This is a sorry situation for I'm sure that over the span of his career Alistair Carmichael has done a great deal more good than harm. Many will be grateful to him for his part in fighting off independence. Most will be aware that no party is comprised of saints.

l recall the shocking scenes on television when Jim Murphy was attempting to electioneer in Glasgow with SNP activists screaming at him and blocking his passage. One shoved a banner into his face. It was the antithesis of fairness and the democratic process. And it wasn't the only such incident reported. But crucially the SNP leadership could disown direct culpability.

I mention it to highlight the frustration politicians like Carmichael must have felt in the heat of the campaign when they saw the electorate slip inexorably away from them.

So does Carmichael deserve a second chance?

That question is not for him, Willie Rennie or someone like me to answer. It's a question that should be put to the voters of Orkney and Shetland. Carmichael should stand down as an MP, offer himself as a candidate to his local party and then seek to be re-elected. Then, if he is re-elected, he will have his second chance.

And he will have deserved it because he will have done the right thing.