Plans to force all schools to teach and uphold "British values" have been announced by the government after the row over alleged Muslim extremism in Birmingham classrooms intensified with the release of long-awaited Ofsted investigations.

Education secretary Michael Gove told MPs there would be unannounced inspections of schools without warning and that a new regime to protect pupils from extremist teachings and culture would be put into place.

"We will put the promotion of British values at the heart of what every school has to deliver for children," he said.

The minister's statement came after much-leaked inspectors' reports into 21 Birmingham schools revealed a culture of "fear and intimidation" in some of the institutions along with a "sudden and deep decline" in standards.

Ofsted head Sir Michael Wilshaw said there was evidence of an "organised campaign to target certain schools", and some head teachers had been marginalised or even forced out of their jobs.

Five of the 21 schools inspected were placed into special measures, where they can be taken over by other schools. One was labelled inadequate for its poor educational standards and another 12 have been ordered to make improvements.

But it was previously unseen details from the report's findings, along with those from the Education Funding Agency, that sparked the greatest concern, coming only hours after leaders of the schools had bitterly rejected the reports as misrepresenting the situation threatening legal action.

They revealed the "unsuitable" phrase "white prostitute" had been used by Muslim staff in assemblies in one primary school and a visit to Saudi Arabia had been open only to Muslim pupils.

In other examples across the schools the call to prayers had been broadcast over a loudspeaker system, pupils were told in biology class "we do not believe in evolution", frightened teachers were forced to meet secretly in a supermarket car park, a nativity play being banned from using a doll as baby Jesus and female staff complaining of unfair treatment.

The schools are at the centre of the infamous "Trojan Horse" letter, widely believed to be a hoax, which claimed there was a plot to take over schools by Muslim extremists.

Sir Michael stopped short of declaring that was the case but attacked Birmingham city council for a serious failure in protecting children from exposure to extremism.

In the Commons, Gove said he would consult on the best way to ensure British values were taught but he faced attack from Labour's Tristram Hunt who said he was equally concerned about the reports' findings but Gove was attempting to evade responsibility.

Gove's pet academies project of taking schools out of local authority control, started by the Blair government, meant there was no local oversight and responsibility fell to Whitehall, namely the education secretary.

Hunt wanted to know why Gove had not acted before, despite claims he had been warned of the problem four years ago.

Earlier, one of the school leaders, David Hughes, rejected the reports saying: "Ofsted inspectors came to our schools looking for extremism, looking for segregation, looking for proof that our children have religion forced upon them as part of an Islamic plot.

"The reports found absolutely no evidence of this because this is categorically not what is happening at our schools,"

And, while it may be that the worst claims of a concerted and planned plot to take over Birmingham schools may not have been proved, there was enough detail in the reports to raise serious concern.

The issue has already damaged Gove and home secretary Theresa May who was also forced to the Commons to explain she had not authorised the publication of a private letter to Gove attacking him for failing to take action over the issue.

She insisted the release was made by her special adviser Fiona Cunningham, who has since resigned over the issue.

But this row still has plenty of life left in it as two of the most senior ministers continue the denials to avoid any blame.

What will worry many, however, is the possibility that the facts of the Birmingham affair will be lost amid the political storm and that ministers will act out of reasons of personal survival rather than getting to the core of the problem.