Since they were invented around 100 years ago, they have become standard issue for police officers and prison guards around the world.

But adjustable metal handcuffs are now being swapped in Scottish jails for a new ‘soft restraint’ made of fabric.

Bright blue with orange straps, the soft cuffs are a far cry from the traditional metal shackles that have long been part of life behind bars.

Instead of a lock and key, the new cuffs are secured with buckles and hook-and-loop fastenings.

In a recent pilot project within Scottish prisons, the soft cuffs were found to reduce conflict between inmates and guards.

Now the Scottish Prison Service (SPS) has confirmed they are being rolled out as part of a shake-up of safety procedures. 

The manufacturers have told The Scottish Mail on Sunday the restraints are designed to be less painful than metal cuffs and are less likely to breach human rights.

Although they don’t have locks, the makers claim they are impossible to escape from once fastened behind a prisoner’s back.

Doug Melia, chief executive of Safer Handling, the company which supplies the soft restraints – called Safety Cuffs – said: ‘Trying to restrain or control a prisoner in metal cuffs can lead to pain or suffering – which could be seen as a breach of their human rights. The soft cuffs are a more ethical option.’

Standard metal handcuffs feature a ratchet that allows them to be fitted tightly around any size of wrist, with a double lock that both secures the cuffs and prevents accidental tightening.

However, they can still cause injuries such as skin lacerations, abrasions, bruising or swelling, as well as pain in a nerve in the wrist, a condition called handcuff neuropathy.

‘But because the soft cuffs are made of fabric they spread the pressure right around the circumference of the wrist, reducing the risk of damage. They’re also easy to adjust should they need to be tightened or loosened,’ Mr Melia said.

However, because they can be undone without a key – for example by another prisoner – the new cuffs are not suitable for every situation.

Mr Melia said: ‘They are best suited for use inside a prison where an inmate is already within a locked building and so isn’t a flight risk.

‘Metal cuffs would still be used for transporting prisoners or if a prisoner is being left unattended.’

Last night the SPS confirmed the roll-out of the soft cuffs – costing around £70 a pair – following the pilot project at Polmont and Stirling prisons and young offender institutions, and HMP Low Moss.

A pain-free technique for restraining prisoners is also being introduced. Designed to keep them on their feet instead of forcing them to the floor, it comes ten years after the death of Alan Marshall, 30, who was restrained face down by up to 17 officers at HMP Edinburgh.