British Prime Minister David Cameron pledges to combat Islamism in schools

"I am hugely concerned about the allegations. I don't want to see Islamist entryism, into our schools. That is a very worrying development," Cameron said.

"We will not have extremism, entryism, Islamism in our schools," he said on "Birmingham Free Radio".

The Prime Minister's comments came as the chief inspector, Sir Michael Wilshaw, put the finishing touches to a damning letter accompanying emergency inspection reports into 21 Birmingham schools.

According to 'The Sunday Times', which had first exposed the so-called 'Operation Trojan Horse' to infiltrate Britain's schools back in March, Wilshaw is understood to be "deeply concerned" by the inspector's findings.

He will call for changes to the rules for appointing and monitoring school governors nationwide, a source told the newspaper.

The UK's schools inspectorate OFSTED's reports, which were due to be published this week, have been delayed until June, after inspectors were asked to investigate three more primary schools in Birmingham.

All the reports will be sent to Michael Gove, the education secretary, next month along with a letter from Wilshaw outlining the problems that have been found.

Gove had faced criticism after he appointed a counter-terrorism expert, Peter Clarke, to look into the claims of "Trojan Horse" plot last month.

It is understood that Gove will also order OFSTED to carry out inspections in schools around Bradford, West Yorkshire, widening the investigation.