The neocons are back. That toxic blend of messianic warmongering abroad and McCarthyite witch-hunting at home – which gave us Iraq, Afghanistan, Guantánamo and the London bombings – is coursing through our public life again. Yesterday the liberal interventionists' hero, Tony Blair, was once more demanding military action against the "threat of radical Islam".

Reprising the theme that guided him and George Bush through the deceit and carnage of the "war on terror", the former prime minister took his crusade against "Islamism" on to a new plane. The west should, he demanded, make common cause with Russia and China to support those with a "modern" view against the tide of political Islam.

But he also demanded military intervention against Syria – backed by Russia – along with more "active measures" to help the armed opposition, which is dominated by Islamists and jihadists. It's a crazy combination with an openly anti-democratic core: the Middle East peace envoy also warmly endorsed the Egyptian dictatorship, along with the repressive autocracies of the Gulf.

Quite why the views of a man whose military interventions in the Muslim world have been so widely discredited, who has been funded by the Kazakhstan dictator and is regarded by up to a third of the British public as a war criminal, should be treated with such attention by the media isn't immediately obvious. But one reason is that they chime with those of a powerful section of the political and security establishment.

In Britain, the campaign against Islamist "extremism" is once again in full flow. In fact, it is open season on the Muslim community. For the past few weeks reports have multiplied about an alleged "Islamic plot", code-named Operation Trojan Horse, to take control of 25 state schools in Birmingham and run them on strict religious principles.

The education secretary, Michael Gove, a long-time neoconservative supporter of Blair's wars and Islamist witchfinder general, responded by sending in an army of inspectors to hunt down extremists and appointing Peter Clarke, the former head of Scotland Yard counter-terrorism, to investigate.

But all the signs are that the anonymous dossier setting out the Salafist takeover plan is a hoax linked to an employment tribunal case. A headteacher the dossier claimed the plotters had ousted in fact left 20 years ago. The only individual named in the dossier isn't a Salafist. Even the West Midlands chief constable described Clarke's appointment as "desperately unfortunate".

But there are now four official inquiries. Inspectors have gone round schools asking teachers whether they are homophobes and telling others their school will fail inspection because they're not teaching "anti-terrorism", while Gove's media allies have been fed inflammatory titbits to justify the campaign.

Locals insist the reality is that Muslims, both liberal and conservative, have been getting more involved in their children's schools to raise standards, not "Islamise" them. But the result of the uproar has been to poison community relations and deter ordinary Muslims from taking part in civic life for fear of being branded "extremist".

William Shawcross, the Charity Commission chairman and another neocon ideologue, has meanwhile declared "Islamist extremism" the "most deadly" problem facing charities and promised tough measures to crack down on it, however it might be defined.

Then the Muslim mayor of Tower Hamlets, the former Labour councillor Lutfur Rahman – often described as "extremist-linked" in the media – has been the target of a new media onslaught. No wrongdoing has been uncovered, including by the police. The communities minister, Eric Pickles, has nevertheless sent in inspectors.

That follows David Cameron's far more ominous announcement of an "investigation" into the Muslim Brotherhood and its links with "violent extremism" both in Britain and abroad, with the possibility of banning it as a terrorist organisation. The motivation for this inquiry into the most influential political organisation in the Muslim world was made transparently clear by the appointment of Britain's ambassador to Saudi Arabia, Sir John Jenkins, to head it. The Saudi and Egyptian regimes both regard the election-winning Brotherhood as a mortal threat and have designated it a terrorist organisation.

So to appease Riyadh, finalise multi-billion pound arms contracts and align Britain with the emerging Egyptian-Saudi-Israeli axis, Cameron has tossed them a bone. If he really wanted to know about the Brotherhood he could have asked its envoy at the lunch he held for him last May at Chequers, before their elected president was overthrown in Cairo's blood-drenched coup.

Alternatively, William Hague could have had a chat with the Brotherhood members of the Syrian rebel coalition Britain backs with cash and equipment, and the US supports with arms. But that might have caused embarrassment to Whitehall officials who insist that young British Muslims going to fight in Syria represent the greatest threat to the country's security.

Which helps to explain the incoherence of Blair's outpourings. Western policy in the Middle East now verges on the surreal. Britain, the US and their friends are in practice lined up with Islamist (and al-Qaida) Syrian rebel forces while claiming they only back "moderates" – but deny the rebels any decisive edge and support the suppression of Islamists across the region.

Muslims from Britain who volunteer to fight or send funds to Syria, in effective alliance with their government, are then arrested and charged with terrorism offences in Britain. Britons who went to fight in Libya in 2011, on the other hand, were allowed to come and go as they pleased.

It is beyond hypocritical and cynical, but is part of a pattern of manipulation, support for tyranny and military intervention in the Middle East over a century. That record has been the central factor in the rise of Islamist movements and the jihadist backlash since 2001. This week's US missile attacks in Yemen, which left dozens dead, will generate more of it.

Meanwhile, in Britain and other countries preparing for next month's Euro elections, denunciations of Islamic "extremism" and non-existent plots, along with dog-whistle talk about Christianity, are the small change of the contest with rightwing populists. But the fear and hatred they feed will be with us for many years to come.

Twitter: @SeumasMilne