The Scottish paper manufacturer said in a statement that the accident took place on Saturday night in a "restricted demolition site, unauthorised access to which is totally prohibited".

It confirmed that a member of staff was currently in "critical condition" in an Edinburgh hospital.

Local reports have said the employee sustained the injuries after falling around 12 feet.

Tullis Russell said: "The injured employee was not on shift at the time of the incident, should not have been present anywhere on the mill site and was not authorised to be present in the demolition area.

"Our thoughts are with the employee's family and friends."

The incident is now the subject of a police investigation and an internal company investigation.

In March this year, the company was fined £260,000 after a worker fell almost 50 feet through a roof to his death.  

Tullis Russell said it could not comment further at this time.