Jeremy Corbyn is perfectly right to relate this week’s Manchester terrorist atrocity to British foreign policy in the Middle East. Whenever Tony Blair, Gordon Brown and David Cameron struggled to explain why British blood and finance had to go on toppling regimes in Afghanistan, Iraq and Libya, they were explicit: it was “to prevent terrorism in the streets of Britain”. The reason was given over and over again: to suppress militant Islam.

When that policy clearly leads to an increase in Islamist terrorism, we are entitled to agree with Corbyn that it has “simply failed”. Regimes were indeed toppled. Tens of thousands died, many of them civilians every bit as innocent as Manchester’s victims. Terrorism has not stopped.

Whenever al-Qaida or Isis seek to explain their atrocities, reference is usually made to British intervention and the military killing of innocent Muslims. It is mendacious to try to sanitise our overheated and jingoistic response to domestic terrorism by pretending that it is unrelated to British foreign policy. It was we who made the link, and before the terrorists did.

The Snap: Corbyn returns to campaign, linking terror at home and wars abroad Read more

Of course this does not exonerate anyone. Yes, militant Islamists are seeking to subvert the west’s sense of security and its liberal values. Yes, the west’s continued bombing of markets, hospitals, weddings and villages is “accidental” – albeit inevitable, given the nature of modern air war.

But we used the language of “shock and awe” in bombing Baghdad in 2003. We gave the current era of Islamist terrorism a cause, a reason, an excuse, however perverted. We committed armed aggression against sovereign peoples who had not attacked us.

Play Video 1:11 Corbyn says 'war on terror not working'

Where Corbyn spoils his pitch is in relating terrorism not just to foreign policy but to domestic austerity. He stoops to Theresa May’s level in seeking to make electoral capital from a tragedy. Were he not grandstanding himself, he could accuse her of peddling the politics of fear by flooding the streets of the capital with soldiers. He could plead with the Muslim community to do more to combat and expose terrorist “grooming”. But there is no evidence that the security services are impeded in their work by staff shortages. It is the one aspect of policing that has been showered with money.

Politicians who exploit moments of public tragedy play a risky game. Whether Corbyn was tactful to return to the election campaign by citing Manchester is moot: he would have been wise to wait a few days. But Islamist terrorism is related to foreign policy. However hateful it may seem to us, it is a means to a political end. Sometimes it is as well to call a spade a spade.