The deadly substance was found at the old St Eunan’s Primary site by contractors who were carrying out routine investigations on the land.

The origin of the asbestos is not known but West Dunbartonshire Council are investigating to identify this as a matter of urgency.

Although the site was secured following the demolition of the school in 2011, the fence has been forced open on occasions and the grounds used as a shortcut by locals.

Following this latest discovery site security is being repaired but there is concern that some people may still attempt to gain access.

Warning signs will be erected this week telling people not to enter the site due to the presence of contaminants.

Councillor Patrick McGlinchey, convener of infrastructure and regeneration, said: “Our first concern is for public safety and we wanted to let people know about this situation as soon as possible. Signage has been ordered and will be erected immediately. We would ask that people respect this advice and do not access the site.

“The asbestos found on the ground is being removed and the council is awaiting further detailed reports on this occurrence. We will take further action as required.”