The school from the television series Educating Greater Manchester has been put into special measures after inspectors found it to be inadequate in all areas.

Standards at Harrop Fold school, which was once rated the worst in the country but was presented as resurgent in the Channel 4 programme and had come to be rated as good by 2013, have slipped to an unacceptably low level, according to Ofsted.

“The school is failing its pupils. Significant and wide-ranging weaknesses have developed over time ... Pupils are not properly safeguarded. The school site is not secure,” the education watchdog’s report said.

Among their findings, the inspectors said performance had been “unacceptably weak”, and that GCSE results “[are] much lower than those achieved by similar pupils elsewhere, and are declining”.

The inspectors added: “Pupils currently in the school do not learn well enough ... Teaching and learning are highly inconsistent in quality. Teachers do not plan effectively to meet pupils’ needs. Teachers’ expectations are too low.”

The problems in the school were highlighted in September, when the headteacher, Drew Povey, quit and a public row erupted between him and Salford city council. He had been suspended in the summer, along with three other members of staff, after the council began an investigation.

He accused councillors of pursuing a “vendetta” against him, saying mere administrative errors had been behind the suspensions. In his resignation letter, he said he took full responsibility for the errors, which involved how attendance, exclusions and home schooling were being recorded, but claimed he had been unfairly treated.

In its report, Ofsted said: “There is currently considerable uncertainty concerning [the school’s] leadership ... Record-keeping about pupils’ attendance, behaviour and safeguarding has been weak.”

Following his resignation, Damian Owen was appointed as the interim headteacher, provided by the Greater Manchester Learning Trust. Ofsted said he had started to address the school’s problems.

In a letter to parents published online, Owen and the councillor Kate Lewis, the chairwoman of governors, said staff were disappointed by the report but determined to “improve the school rapidly”.

The council said the Department for Education would identify an experienced academy sponsor to support the school, which has 860 pupils aged 11 to 16.

Educating Greater Manchester, first broadcast in August 2017, was the fifth edition of Channel 4’s Educating … series. Last January, Channel 4 announced it would film two more series at the school, the first time it would return to the same location.