When Broadmoor’s sirens go off, a “cascade system” is supposed to operate, where each of the 26 schools contact one another to raise the alert.

However, councillors heard that when asked in a survey about how well the alert system was operating, only 12 of the schools responded. Of these, a quarter said they had not had a test for at least a year.

The survey was commissioned by Wokingham Borough Council’s Overview and Scrutiny Management Committe and the results were discussed at their meeting on Monday night.

The results revealed that Winnersh Primary School had “not received any correspondence on the issue in the last two years.” The head teachers of Farley Hill Primary School and St Crispin’s School were “not aware of the school receiving a test alert in 2014”.

The cascade system is intended to work alongside the satellite sirens around the site, which were introduced after a patient escaped in 1953 and murdered a pupil in Arborfield.

Now the West London Mental Health NHS Trust wants to deactivate most of the alarms and leave only six new, more powerful ones active.

Speaking at the meeting, Councillor Malcolm Richards said if all 12 sirens were replaced it would cost the trust £400,000.

A report by Michael Firmager, vice-chairman of the committee, said: “I must add the security measures are incredibly stringent and escape is now most unlikely.

“The last escape was back in 1993 before the current security measures were put in force.

“With the fences, you are unable to put fingers through. Any attempt to climb, or if the fence is hit hard, then the alarms go off and the cameras in that area are automatically directed to that part of the fence.

“There are anti-climb measures on top of the fence. In total there are 307 cameras.” The committee agreed to re-contact the 14 schools who had not replied to the survey, and results would be discussed at the next meeting in March.