Scotland’s biggest jail for young offenders is increasing security amid concerns about criminals scaling internal walls.

The prison near Polmont has ordered five new state-of-the-art CCTV cameras to be installed around the perimeter.

High-powered LED lights will also be purchased to provide a “four-metre strip around the complete external perimeter,” according to documents seen by the Herald on Sunday.

A prison spokesman said the increased security was prompted by incidents which saw young offenders clamber on top of eight-feet high covered walkways which connect buildings on the estate.

Her Majesty's Young Offenders Institution (HMYOI) Polmont is designed to hold more than 800 prisoners, including around 100 women who were transferred from Cornton Vale.

The majority of inmates are aged 16 to 21 and are serving sentences ranging in length from six months to life.

Many of them use illegal drugs which can be thrown over prison walls. A third of inmates in Scottish jails tested positive for banned substances ahead of their release, according to the Scottish Prison Service figures.

One prison governor said there are “productive ways of putting things into prisons”. Ian Whitehead, who was governor of Barlinnie before becoming director of Addiewell, said in 2014 that banned substances have been found in tennis balls, volleyballs and plastic Kinder Surprise eggs which have been lobbed over perimeter fences.

Seven members of a gang which used drones to fly more than £500,000 worth of drugs into prisons in England were jailed on Friday.

The Scottish Prison Service (SPS) plans to buy five new pan–tilt–zoom (PTZ) cameras capable of remote directional control which will be fixed to the outside of the perimeter wall.

SPS documents seen by the Herald on Sunday said: “HMYOI Polmont requires increased CCTV surveillance exterior to the perimeter wall. The full project is the design, supply, installation, test, integration and commissioning of this increased CCTV coverage.

“The works shall include installation of three new CCTV camera poles with PTZ cameras, and at two further camera poles that are already installed removal of fixed cameras and installation of PTZ cameras.”

The documents also reveal plans to install “increased lighting external to the perimeter”.

“External perimeter lighting shall provide a well-lit area in the form of a four-metre strip around the complete external perimeter,” the document said. “The perimeter lighting shall provide both a safe route for inspection of the perimeter, and increased lighting to facilitate external CCTV camera operation.”

The prison in Polmont is surrounded by houses and residents have yet to be told about the plans.

“It’s the first I’ve heard,” said Margaret Law, whose back garden adjoins the perimeter wall.

Neighbour Elizabeth Johnstone added: “I don’t want light pollution or cameras looking into my house. We already get a lot of hassle with the noisy prisoners shouting and swearing at each other.

“You would think the prison would have told us. They’re usually quite good at letting us know what’s going on.”

Local councillor Malcolm Nicol was also kept in the dark. “First I’ve heard,” he told the Herald on Sunday.

Nicol wrote to Falkirk Council’s planning department to ask if the prison service had requested permission to install new CCTV and LED lights.

“We haven’t received any enquiries from the prison about this proposal,” said Bernard Whittle, the local authority’s Development Management Co-ordinator.

“It looks like a planning application may not be required. HMYOI Polmont is Crown Land. There are extensive permitted development rights that apply to Crown Land and that allow various developments to be carried out without the need to obtain a planning permission from the council.”

When the Herald on Sunday asked the SPS whether the changes to security had been prompted by concerns about drugs coming over the perimeter fence a spokesman said: “The issue is people climbing on internal covered walkways. It’s about preventing people going on walkways and having a better visibility of those areas if they do get up there.”