For a country constrained by economic sanctions, and at the centre of a dangerous military and diplomatic crisis, the Islamic Republic of Iran looks and feels surprisingly relaxed. There are no checkpoints on the roads, or armed soldiers on the streets. Courting couples hold hands as they stroll the pavements. Women parade their make-up, hair and skinny jeans. The shops and bazaars are humming. Even as elements of the regime’s notorious Quds brigade move in to central Iraq to prop up its government, no sense of panic intrudes on the country’s daily life.

With good reason. Iran is on the up. It has cause to feel confident that, after 35 years of revolution, things are going its way. An impotent West must contemplate the unthinkable: allying itself with the mullahs of Tehran to stop the sudden, relentless advance of Sunni extremists in Iraq who seem on the verge of creating a new, potent terrorist enclave within striking distance of Israel, Nato Turkey, the Gulf and the remaining pro-Western regimes of the Middle East.

These are some of the impressions I came away with after spending the past week driving through central Iran. Such snapshots are by their nature unreliable: Iran is a country built on relentless propaganda and run by a government that does its best to keep its population cut off from outside influences and information. Of course things are going well, if there is no evidence to the contrary. The tell-tale signs of rot – the steady collapse of the currency for starters – are predictably attributed to Zionist plots and foreign conspiracies. Boulevards are lined with posters of martyrs of the Iran-Iraq war, the murderous conflict that was supposed to stop Shia Iran from dominating the region. Yet now, as Con Coughlin noted a few days ago, Iran looks a winner.

The day I left London, Michael Gove was being taken to task for pointing out that the contagion of murderous Islamism presents an imminent danger to us here in Britain. His concern was for schools in the Midlands with predominantly Asian students, where inspections had found evidence of teaching that fostered community separation and suspicion of, if not hostility to, non-Muslims. As an eloquent analyst of the threat of extremism in the UK, Mr Gove has consistently pointed out that the West and its values are being targeted by a deathly ideology that has penetrated our society. He will take scant satisfaction that his concerns look prescient.

Our mistake is to think that the events in Iraq do not lead straight back to us. Yet if one tears one’s gaze from there to connect the dots, the pattern is plain to see. In Brunei, the Sultan, obscenely wealthy, pushes his impoverished country backwards by imposing sharia, all the while expecting us to increase his riches by continuing to patronise the Dorchester hotel, which he owns – in Hollywood and London, celebrities and businesses have thought otherwise and are boycotting his companies. In Nigeria, the world is slowly forgetting the hundreds of Christian girls kidnapped and forcefully converted by Boko Haram, which marches on with impunity. In

Kenya yesterday, al-Shabaab militants attacked beach resorts, killing 49 people. In Israel, Islamists have kidnapped three Jewish teenagers. Pakistan launches strikes on militant bases in its tribal areas, while British intelligence worries about the ways extremists from the Kashmir valleys find willing supporters in the backstreets of Bradford and Skipton. There are 500 British jihadists fighting in Syria. Libya is Balkanised. Iraq is collapsing.

Our fear of demonising Islam and British Muslims means we worry about speaking out about the medievalism at the heart of this ideology, which has no more to do with Islam than the gay-hating, Koran-burning Westboro Baptist Church in Florida has to do with Protestantism. Islam is a convenient deflector for a cultural outlook that rejects education, science, culture, human rights and the central place of women, the hard-won building blocks of civilisation of any kind. Do we not wonder why it is necessary to mount government campaigns against forced marriage, as was done yesterday, or against female genital mutilation? Backwardness promoted under cover of Islam reaches into our own communities.

It is a measure of how confused and chaotic the West’s policy towards Iraq and Islam has become that Iran has gone from pariah state and charter member of the Axis of Evil to a legitimate interlocutor in the struggle against a more terrifying force. One can almost feel the relief of diplomats saying to themselves, “at least we can reason with them”. No wonder. Iran has been engaged in intensive diplomacy in Geneva ahead of the July deadline for a deal on its nuclear ambitions. Its diplomats are familiar and admired. It will doubtless calculate that its hand has been strengthened in the negotiations. The realisation in Washington, London and elsewhere that a vast, strategically important area is in the hands of a gang of obscurantist crazies with money to burn and a taste for crucifixion has suddenly made Iran a necessary interlocutor. As William Hague told the Commons yesterday: “We do have many common interests with Iran,” including stability in Afghanistan and Iraq.

It would be a mistake typical of how we have approached the politics of the region to get carried away. “My enemy’s enemy is my friend” is a necessary calculation of any diplomacy, but it has been our desire to divide good guys from bad guys, to pick winners and losers, that has led us to fail repeatedly. When Rory Stewart, the new head of the Commons defence select committee, who served in Iraq, said yesterday that we should concentrate on what we can do, not what we ought to do, a necessary dose of realism began to penetrate the debate. The millennial sectarianism that pits Shia against Sunni, as refracted through the prism of regional power politics drawing together Egypt, Israel, Syria, Iraq and Iran, remains beyond our ability to shift, save at the margins.

Tony Blair, roundly castigated as mad here and elsewhere for daring to say that the week’s events cannot be blamed on his military adventurism, was surely right when he said that the cause of the crisis lies within the region, not outside it: “At its simplest, the jihadist groups are never going to leave us alone. This is our struggle whether we like it or not.” Yet it is because we have been unable to separate the cultural from the religious, the medievalism from Islam itself, that we have indeed struggled. Apart from confirming that there is no military option for us to take, nothing better illustrates the impotence of our response than the announcement yesterday that Isis has been added to the list of proscribed organisations in the UK. As if they care.

Iran at least is a state, and one with interests that may at times coincide with ours. The Foreign Office is ready to announce the restoration of diplomatic relations. But we shouldn’t rejoice at that. Iran’s ambition to promote Shia sectarianism is just as poisonous. One has only to consider the corruption and viciousness of its client government in Baghdad.

In Tehran on Saturday, I met a student leader, one of those who in 2005 invaded the British embassy and precipitated the break in relations. “Everything the West has done around here has backfired, and we have emerged stronger,” he said. He looked very relaxed.