An investigation has been launched into a disturbance involving about 40 prisoners at a Scottish jail.

The Scottish Prison Service (SPS) has confirmed that inmates at Perth prison refused to return to their cells at about 2230BST on Tuesday.

The fire brigade was also called to deal with a small fire at the prison which is believed to have started during the disturbance.

The inmates returned to their cells in the 'C' Hall block of the prison about an hour and a half later.

Clive Fairweather praised prison staff

An SPS spokeswoman confirmed that an investigation into the incident was under way.

She said the jail houses mixed categories of prisoners.

At the beginning of May, government inspectors welcomed progress on improving conditions at Perth which, they said, had suffered "many years of neglect".

An official report from HM Chief inspector of Prisons Clive Fairweather praised recent investment at the jail.

'Unacceptable conditions'

He and his team said they were particularly impressed by the "professionalism and dedication" of staff.

But he also criticised the conditions experienced by short-term prisoners housed in C Hall.

The report added that conditions in the block were "unacceptable".

"Its old gallery structure, total lack of integral sanitation and in-cell electrical power, indicate that fundamental restructuring is long overdue," Mr Fairweather said.

There has been a series of incidents at prisons

According to the Scottish Prison Service website, Perth holds short term (less than four years) local adult male prisoners, including fine defaulters, and those on remand from the courts of Angus, City of Dundee, Perth & Kinross and the northern part of Fife.

The establishment also accommodates in secure conditions long-term adult male prisoners, including category A prisoners who are serving sentences of up to life imprisonment.

Over the next three years it will concentrate on taking its long term prisoners from the north and east of Scotland.

It provides a national resource through a small unit for prisoners who have been disruptive in mainstream and require intensive staff/prisoner interaction.

The disturbance is the latest in a series of incidents at Scottish jails.

Inmates barridaded themselves into a section of a hall at Saughton Prison, in Edinburgh, in May.

In April, there were stand-offs involving inmates at Low Moss, near Glasgow, and Shotts Prison, in Lanarkshire.