There is compelling evidence that a hardline Sunni Islam agenda was at work across Birmingham schools caught up in the alleged "Trojan Horse" plot, a damning inquiry report has concluded.

The probe, headed by former Metropolitan Police counter-terrorism chief Peter Clarke, was commissioned by the Department for Education (DfE) to investigate more than 20 city schools and has been looking at the background behind the key allegation that a clique of governors was attempting to seize control of schools, and force out unco-operative headteachers.

According to the Guardian newspaper, which has seen a leaked draft of the full report due out next week, Mr Clarke concludes there was a "sustained, co-ordinated agenda to impose segregationist attitudes and practices of a hardline, politicised strain of Sunni Islam".

He said: "The agenda, but not the tactics, involved stem from an international movement to increase the role of Islam in education."

The report states: "Left unchecked, it would confine schoolchildren within an intolerant, inward-looking monoculture that would severely inhibit their participation in the life of modern Britain."

Its conclusions are heavily critical of Birmingham City Council in failing to support teachers and governors, adding that there is "incontrovertible evidence" that the council was aware of practices similar to those alleged in "Trojan Horse" for many months, yet did nothing.

The council's own separate inquiry report led by Ian Kershaw is due to be published later today.

Mr Clarke concludes there was "no systematic attempt to deal with the issue" by the council, despite Trojan Horse-type concerns being known to senior council officials in late 2012.

On academies, which are the responsibility of the DfE, "the inquiry has highlighted there are potentially serious problems in some academies", but does not criticise the academisation process.

Mr Clarke recommends a tightening of the rules around academies' governance monitoring, the setting up of academies, and the establishment of academy chains.

The report, commissioned by former Education Secretary Michael Gove, also recommends greater powers for the Secretary of State to be able to block certain individuals from managing schools.

The DfE report is the latest of four separate probes into "Trojan Horse".

Earlier this year, Ofsted investigated 21 schools over the allegations, placing five into special measures, and leading Chief Inspector of Schools Sir Michael Wilshaw to conclude "a culture of fear and intimidation has developed in some of the schools", while safeguarding pupils against the risk of extremism was found to be lax in many classrooms.

The Education Funding Agency has also investigated, while both the council's and the formal publication of Mr Clarke's report are now imminent.

Within Mr Clarke's report there is also criticism of Tahir Alam, former chairman of trustees at Park View Educational Trust which ran three of the schools investigated.

It concludes: "Many of the governors who have caused most difficulty on governing bodies have connections to Mr Alam and Park View school."

On Tuesday, Mr Alam resigned along with the entire trust board, but said he was "proud" of the trust's achievements raising education standards and claimed Park View had been victim of "a vicious and co-ordinated offensive against the trust and its schools".

The trust's schools - Park View Academy, Nansen Primary and Golden Hillock -were three of five city schools placed in special measures.

A DfE spokesman said it did not comment on leaks but added: "The allegations made in relation to some schools in Birmingham are very serious and we are investigating all evidence put to us in conjunction with Ofsted and Birmingham City Council.

"In June, Ofsted identified concerns at a number of schools and action has been taken.

"Schools that are proven to have failed and without the ability to improve will be taken over and put under new leadership, and any school could now be subject to rigorous on-the-spot investigations with no advance warning.

The spokesman said the Clarke report would be published "shortly", adding: "It is absolutely vital this investigation is carried out impartially, without pre-judgment."

"It would be inappropriate to comment further at this stage."