Pupils at prestigious Henrietta Barnett School have been disciplined after performing a “strange” ritual in a strictly off-limits loft, it is claimed.

The high-achieving grammar school strongly denies that sixth formers were in an out-of-bounds attic above their common room holding a “seance”, despite two sources close to the school making the claim.

One report suggested the pupils were found after falling through a ceiling, in the lead up to the Halloween half-term break.

But the school has said there was only minor damage to some plasterboard as sixth formers descended from the loft.

A source, who wished to remain anonymous, said: “They were in a restricted area of the school, somewhere they never should have been. They were doing these silly, strange things, but I’m not entirely sure what. No-one was hurt.”

London Ambulance Service said there had been no call-outs to the school in recent weeks.

The Hampstead Garden Suburb school in Central Square has confirmed that members of the sixth form were “internally excluded” from the school before half-term.

A deputy head at the school said: “At the beginning of October, a small number of sixth form students who were in their common room during morning break made a spur of the moment decision to enter the attic space above their study space.

“They very soon realised that this was potentially dangerous, as the attic is out-of-bounds and is not a safe area.

“They returned to the common room within a few minutes and we are grateful that no-one was harmed or injured.

“As they came back down, however, some minor damage to the plasterboard occurred. With hindsight, the students realised this had been a foolish and impetuous idea.

“Following the incident, however, they responded very responsibly and informed a member of staff.

“The school was concerned that students acted in a way that may have put their safety at risk and dealt with the matter quickly with sanctions and by meeting the girls and their parents to discuss the inherent dangers of accessing off-limit spaces.

“The girls have learnt from the experience and are now continuing their studies.”