Footage has emerged of a prison inmate passed out after apparently taking a legal high known as "spice".

The video was reportedly filmed by another prisoner at HMP Addiewell in West Lothian on November 1.

It shows a man lying face-down on the bed while others laugh and shout at him to get up.

At one point during the three-minute clip a man slaps him repeatedly on the head in an attempt to wake him.

A source claimed the men were "out their faces on spice" and trying to sneak the man back on to their wing.

Three HMP Addiewell prison guards were recently taken to hospital after accidentally inhaling spice, which had been smoked in a cell.

Legal highs such as spice - formally known as new psychoactive substances or NPS - were banned last year.

It is also illegal to have a mobile phone in prison.

Spice is a synthetic cannabis substitute often branded a "zombie drug" because of the stupefying affect it can have on users.

Inmates are also smuggling a potent camabinoid known as "annihilation" into HMP Addiewell, it has been claimed.

Stevie Farrell from the Community union, which represents officers at the jail, has called for action on the use of NPS in prisons.

He said the difficulty detecting NPS potentially makes them more dangerous than conventional drugs such as heroin and cocaine.

"It's a difficult situation - this is a wider issue than just at HMP Addiewell,"he said.

"It needs a round table discussion at the highest level in Scotland. Quite frankly there is no way to detect these substances coming into prisons.

"Years ago it was cannabis and it moved on to heroin and cocaine and now it's new psychoactive substances like spice."

The Scottish Prison Service said it was "not aware" of the incident shown in the video but Sodexo, which runs HMP Addiewell on its behalf, is investigating.

"Prisons are a challenging environment to manage and the safety of staff, prisoners and visitors remains our top priority," a Sodexo spokesman said.

"The use of psychoactive substances is a challenge across the whole prison estate and staff at HMP Addiewell are working in partnership with Police Scotland to tackle this issue.

"The possession of a mobile phone in prison is a criminal offence and anyone found in possession of illicit articles is reported to the police."