We must play our part in the fight against Isis

When the House of Commons sits on Friday, recent history will repeat itself. Last August, the House was recalled to debate air strikes against the Syrian regime. Sometimes history does not even rhyme; it just clashes.

Much has been made of the paradox that MPs were asked last year to approve strikes against Bashar al-Assad, whereas this year they will be asked to take a view on strikes against the other side in Syria’s civil war. But something important has changed since then, and British public opinion has shifted. Since last August, Isis has crossed the border from Syria to Iraq in force and taken over large areas of the country. It has imposed its horrific rule in the corridors it controls, using terror as an instrument of oppression and killing Western hostages for propaganda.

Last year, the British people – and MPs represented them accurately – were not persuaded of the case for air strikes to punish Mr Assad for the use of chemical weapons. As Ed Miliband said, it turned out that there were other methods of dealing with the question, and Mr Assad has now been disarmed of his illegal weapons by international agreement.

This year, however, the British people might be persuaded that there is a case for UK forces to take part in air strikes to push Isis back from Iraq. The case for military action this time is completely different from that which Mr Cameron tried to make last year. MPs need to consider it from first principles, putting aside what has gone before. The same goes for the arguments about the invasion of Iraq in 2003. Plainly that contributed to the desperate state of Iraq over the past 11 years, but it is not directly relevant to the question that will be before the Commons on Friday.

This time, the sovereign and democratic government of Iraq is asking for help in defeating a terrorist insurgency. Of the justice of that cause there should be no doubt. The murderous ambitions of Isis against the “wrong” kind of Muslim and the adherents of other religions and none are genocidal in nature, and the international community has a responsibility to protect the people of Iraq – and of Syria and elsewhere.

That does not mean, of course, that UK forces have to be part of the international response, because there are other conditions that must be met – and it should be the purpose of a Commons debate to test them. One is that the objectives of air strikes should be clear and achievable. Another is that they should be legal. In the case of air strikes in Iraq, we believe that those tests are likely to be passed.

There are two, linked objections that we do not share. They are that we should leave it to the US and its Arab allies. If they are prepared to do it, why should the UK make itself a target? That is not a noble objection, but it ought to be considered. We reject it because the jihadist ideology is a threat to us anyway, and, if it is right for other countries to do it, Britain should play its part.

The difficult part for Friday’s debate is Syria. Air strikes against Isis in Syria could be legitimate on humanitarian grounds, but it is harder to be sure about their consequences. Mr Miliband found himself in a difficult position this week. He said he supported the US and Arab states’ strikes in Syria but when asked if Labour would vote for UK forces to join them, he said that there was a “higher bar” to be cleared, and mentioned the need for a United Nations resolution.

This appears contradictory: if the UK has a duty to help fight Isis in Iraq, surely it should do so wherever it would be effective? Mr Miliband would be wrong to allow Russia and China a veto at the UN. There could in principle be a case for the UK to be involved from the air in Syria, but let us focus on pushing Isis back in Iraq first.