Leaders of the country’s biggest classroom union have intervened to help resolve a festering crisis at one of Britain’s most famous comprehensives.

Teachers at Holland Park school in west London say they are being reprimanded in public places, have their lessons observed without warning as often as twice a day, and that all their mail is opened, unless it is marked private.

Members of the National Union of Teachers at the school - two-thirds of the 100-strong teaching staff - have declared themselves in dispute with the school over the behaviour of senior management, led by modernising headteacher Colin Hall.

Their complaints of bullying, initimdation and failure to consult staff are the latest manifestation of a staff revolt that has been growing ever since Mr Hall became head of the 1500-pupil comprehensive in early 2001.

The school, once famous for its progressive ethos, was where politicians Tony Benn and Shirley Williams and the actress Vanessa Redgrave sent their children. But Mr Hall, a Blairite moderniser, has upset teachers - many with very long service at the school - and some parents by introducing setting, uniform and rigorous target-setting.

Results have improved but many staff have left and some teachers and parents have attacked his “autocratic” style.

On Monday, Steve Sinnott, deputy general secretary of the National Union of Teachers, heard a catalogue of complaints at a highly-charged meeting at the school attended by 41 members of the union. One teacher who spoke was in tears.

Teachers complained that they were openly reprimanded in corridors, and had their lessons observed with “unreasonable regularity” without warning or clear objectives.

They said senior management were trying to impose unreasonable targets on them as part of performance management reviews and that staff who did not meet deadlines were “named and shamed” in the school’s weekly bulletin.

They also claimed extra pressure was being put on members recently returned from sick leave.

Union members also accuse senior managers of violating their privacy by removing personal belongings and curriculum materials without warrning.

Staff who are not considered to be “on board” with the leadership group’s strategy are penalised by being denied pay rises or promotion, claim NUT members. Some appointments have been made without advertising or formal interview, they add.

But members were not allowed to name Mr Hall or any other members of his leadership group at the meeting. It only went ahead after an assurance by NUT rep Stephen Kruger to the senior management that they would not be identified in relation to any of the complaints.

Last year, an inspectors’ report praised Mr Hall’s “strong and inspirational leadership” and said Holland Park was an improving school that had improved faster under him.

Shortly after, the chair of governors, Sarah Macdonald, resigned.

In response to the complaints about bullying and intimidation by senior management, Mr Hall said: “None of the comments made in the (NUT) paper have been subject to any appropriate or formal procedures.”

He also pointed out that the behaviour of every member of staff in the school, including himself, was monitored by Kensington and Chelsea council.