A further six prison officers were taken to hospital after inhaling fumes from a drug known as Spice, it has emerged.

A total of nine staff became ill at HMP Addiewell in West Lothian after breathing in second-hand smoke from the drug at the weekend.

It was originally thought three staff were affected but the private firm that runs the prison has now confirmed six more also took ill.

Spice, also known as the zombie drug for the effect it has on users, is a so-called legal high which was banned by the Home Office last year.

Union officials have said the synthetic cannabis substitute is a growing problem in Scottish prisons.

Lothians MSP Neil Findlay said he would be speaking to prison management about the extent of the problem.

He said: "I'm very concerned. Prison staff are going to work and their health is being affected by inhaling drugs.

"That should not happen irrespective of where people work. People who go to their job should go in the knowledge that they will be safe there and they're not going to experience things like this."

Sodexo, which runs the 796-place maximum security prison, said there had been no further cases reported since Monday.

A spokesman for the prison said: "We can confirm nine staff were taken unwell while on duty between Saturday and Monday and were taken to hospital.

"The safety of prisoners and staff is a top priority and we are carefully monitoring this issue to ensure that the most appropriate action is taken.

"We are working closely with the police and NHS to tackle drugs and the associated issues which are a significant challenge across the whole prison estate."