Jeremy Corbyn has one attribute essential in any leader: grace under pressure.

One after another of his Shadow Cabinet colleagues has publicly disagreed with his refusal to support the Government's proposal to join the French air force in bombing Islamic State in its Syrian redoubt. Yet the Labour leader yesterday gave a good-humoured and serene defence of his position to the eponymous presenter of the Andrew Marr Show.

Corbyn summed up his adamantine position to Marr with the resounding phrase: 'You don't bring about peace by bombing.' But the Labour leader and his closest colleague, Shadow Chancellor John McDonnell — who backs him over Syria — have not always been of the view that bombing cannot help bring about peace.

On the question of whether Labour MPs will be given a free vote Mr Corbyn said no decision has yet been made

Mr Corbyn was spotted at the London Climate March as part of march events around the globe yesterday

While they have had a totally consistent opposition to any bombing carried out in the past by British or American forces — which would presumably include that of Hiroshima and Nagasaki, which actually did bring to an end World War II — they have had a rather different outlook when it comes to the bombings carried out by the Provisional IRA against British civilians.

In 2003, McDonnell, addressing the Wolfe Tone Society — which labels itself 'an Irish republican support group based in London' — called for IRA members to be 'honoured' and argued 'it was the bombs and bullets and sacrifice made by the likes of Bobby Sands that brought Britain to the negotiating table'. So that indiscriminate bombing campaign was good, apparently.

Torturing

Mr Corbyn has not expressed those views so directly as his friend and ally, but he was the general secretary of the editorial board of the hard-Left London Labour Briefing, which in its contemporary article on the IRA bombing of Brighton's Grand Hotel in 1984 — an almost successful attempt to murder the entire British Cabinet — said the atrocity demonstrated that: 'The British only sit up and take notice of Ireland when they are bombed into it.'

The same edition of London Labour Briefing — for which Corbyn had written the front page story — contained a reader's letter that hailed the 'audacity' of the IRA's attack and said: 'What do you call four dead Tories? A start.'

Jeremy Corbyn, so far as I am aware, has never disassociated himself from anything that appeared in this newsletter. Now, there is nothing immoral in the position he and McDonnell took: that our government's role in Northern Ireland was 'British imperialism'. It is perfectly reasonable for a Briton to choose to be in favour of a united Ireland.

Jeremy Corbyn has a long history of sympathy for the Irish Republican cause, once heading the editorial board of a hard-left newsletter that hailed the IRA murder of four Conservatives as 'a start'

Mr Corbyn addressed the crowd just hours after appearing on the Andrew Marr show and speaking about Syria

Mr Corbyn, five years after he became an MP, was happy to speak at a commemoration for dead IRA terrorists

But what is striking is how Corbyn and McDonnell were not on the side of those who wanted to address the problem of a divided country by purely peaceful means. Corbyn voted in Parliament against the 1985 Anglo-Irish Agreement — the first step towards what became known as 'the peace process'. McDonnell opposed the original negotiations to set up a power-sharing assembly — the basis for the Good Friday Agreement.

Neither of them ever offered support to John Hume, the Catholic leader of the SDLP, who won the Nobel Peace Prize in 1998 (jointly with the Ulster Unionist leader David Trimble) for his earlier attempts to resolve the Unionist-Nationalist dispute by purely peaceful means.

Instead, Corbyn and McDonnell gave comfort to those Republicans whose methods were based on bombs (not to mention torturing members of their own community suspected of disloyalty).

Thus Mr Corbyn, five years after he became an MP, was happy to speak at a commemoration for dead IRA terrorists, at which the official programme had pronounced that 'force of arms is the only method capable of bringing about a free and united Socialist Ireland'.

This last phrase is significant. It is hard to avoid the impression that Corbyn and McDonnell's indulgence of the IRA was connected to the fact the organisation portrayed itself as a hard-Left independence movement. In other words, their apparently principled opposition to bombing weakens somewhat when those doing the bombing can parade themselves as diligent Marxists in the battle against 'imperialism'.

In this context, Ken Livingstone's recent contribution to the debate over Syria is relevant. The former Mayor of London was a close colleague of John McDonnell for many years, took a similar view of the Irish issue — and has recently been appointed by Corbyn to review Labour's defence policy.

Mr Corbyn's deputy Tom Watson and the Shadow Foreign Secretary Hilary Benn – who is tipped as a possible interim leader if Mr Corbyn is ousted – have publicly refused to back him over his opposition to airstrikes

On the BBC's Question Time last week, Livingstone appeared to express some respect for the British Islamist terrorists who used suicide bombs to murder 52 Londoners in July 2007.

He said they had 'given their lives' in protest against the Iraq war — and went on to argue that Tony Blair, in deciding to join in the U.S. invasion of Iraq in 2003 was therefore responsible for the deaths of those Londoners (and the maiming of many more).

Asked about Livingstone's remarks by Marr, Corbyn yesterday refused to criticise them, but added that he preferred to recall what his friend Ken had said at the time.

Livingstone's actual words then were: 'This was not a terrorist attack against the mighty and the powerful. It was not aimed at presidents and prime ministers. It was aimed at ordinary working-class Londoners.'

Murderous

In other words, it was politically unacceptable because the targets were the workers. Someone should tell Ken and Jeremy that the vast majority of the IRA's victims were 'workers', too.

Corbyn yesterday argued, along the same lines as Livingstone, that dangerous 'radicalisation' of Muslims in the UK would be a consequence of our bombing in Syria against Islamic State. Yet neither Livingstone nor Corbyn seem able to say whether a murderous reaction to British foreign policy on the part of disaffected young Muslims would be wicked or even mistaken.

I suspect that is because they see those youths, too, as the helpless victims of 'imperialism' and therefore, in some strange way, unaccountable for their actions.

In certain respects, there is something admirable in Corbyn's resolute adherence to stick to what I suppose we mustn't call his guns. Politicians are always criticised for their inconsistency: here is one who never deviates from his principles.

The problem is that the Labour leader is not the pacifist he appears to be.

He declares himself opposed to bombs, on the principle that they can't bring peace. But when those bombs were directed against the British people, he and his Chairman Mao-quoting Shadow Chancellor seemed only too keen to support the political purpose of those who detonated the explosives.

Plane Stupid Fools Must Pay

Plane Stupid, the aptly named anti-climate change protest group, last Thursday caused hundreds of holidaymakers to miss their flights from Heathrow after activists padlocked themselves to a stationary vehicle in the tunnel leading to the airport.

Perhaps the police might have moved faster: it took them until 11am to re-open the tunnel, having been alerted to the blockage at 7.42am.

But the real responsibility for the misery of so many families rests squarely with those who chose to obstruct their route — and in a way that was potentially most dangerous.

Plane Stupid’s spokesman, Cameron Kaye, argued that this was trivial compared to the risk that expansion of Heathrow presents of ‘wiping out 55 per cent of all species this century’.

In the real world, his actions will not preserve the life of a single insect.

But what about the economic costs to humans in the here and now? Who will reimburse those passengers, whether holidaymakers or businessmen, forced to pay for new tickets?

Is there any reason why those who are out of pocket should not combine together to bring an action for damages against Plane Stupid or, if the organisation has no financial assets of its own, then against the individuals who chained themselves in the Heathrow tunnel?

If there are few worse crimes than the sexual abuse of children, it follows that to fabricate claims of such offences is especially wicked.

Last week, the Mail reported how a 32-year-old teacher, Eleri Edwards, who had been sacked from her job at a school in North Wales, took revenge by making ten separate false allegations of child sexual abuse against the headmaster, Tudur Williams: she did this by pretending to be a young pupil at the school when making the claims to the Childline website.

Ms Edwards has been struck off as a teacher. But the police have brought no charges against her: she has been let off with a caution. If I were Mr Williams, I would not feel that an attempt to destroy my life had been dealt with appropriately.