POLICE in Scotland were seconded to a disgraced undercover unit whose officers had sex with the women they were spying on, it has finally been confirmed.

Scottish involvement in the National Public Order Intelligence Unit (NPOIU) was laid bare in a letter by a UK police chiefs' body that is coordinating the response to the official inquiry into undercover activities.

However, Police Scotland has refused to say how many serving and retired officers worked with the NPOIU.

The NPOIU was set up in 1999 to combat domestic extremism, but ended up deploying undercover officers into peaceful protest groups.

Although it was based south of the border, the NPOIU operated in Scotland, such as embedding officers like the notorious Mark “Stone” into groups at the G8 summit in Gleneagles.

The NPOIU and a separate unit, the Special Demonstration Squad, became discredited after it emerged that some of their officers had deceived the woman they were spying on into sexual relationships.

Other practices included officers disappearing from the women’s lives after faking mental health problems.

Theresa May, as Home Secretary, tasked Lord Justice Pitchford to lead an Inquiry into the units and the wider issues surrounding undercover policing.

Despite proof that operations took place here, the inquiry does not extend north of the border and it was never confirmed whether officers who worked for Scottish forces were seconded to the NPOIU.

However, the National Police Chiefs Council, which is helping forces meet the requirements of the inquiry, has revealed for the first time the Scottish police involvement.

In a letter sent by the NPCC’s Andy Ward to Police Scotland Deputy Chief Constable Johnny Gwynne, he wrote: "I sent out the below to the forces around E&W earlier in the week but then of course realised that, whilst Scotland does not fall within the TofR for the Inquiry, [redacted] number of staff from Scottish forces, currently both retired and serving, were seconded to the NPOIU during its lifetime.”

He added: "Forces will be expected to pick up the costs for officers/staff from the NPOIU (serving or retired) for who they have welfare responsibility."

It is understood the NPOIU had various tiers of staff – undercovers, officers who handled the so-called “spy cops”; and management.

The organisation and other units were eventually merged and became the National Domestic Extremism Unit.

Labour MSP Neil Findlay said: "The NPCC have confirmed what the dogs in the street already knew – that Scottish police officers were seconded to work for the discredited NPOIU. What is galling though is the fact that Scottish victims will not have access to justice via a Scottish inquiry. The UK and Scottish Governments should ashamed of that.”

Paul Heron, a solicitor with the Public Interest Law Unit at Lambeth Law Centre, said: "What is becoming increasingly clear is that the NPOIU had a role not just in England and Wales, but most likely an active role in Scotland. It therefore continues to make no sense as to why the public inquiry currently examining the role of undercover policing of trade unionists, socialists, anti-racists, MPs, and women activists does not extend north of the border. It is time for either the Pitchford inquiry to be extended to include Scotland, or the Scottish Government orders its own public inquiry along the same lines – truth and justice demands it."

Police Scotland Assistant Chief Constable Steve Johnson said: "Like other forces in the UK, an opportunity has existed for legacy forces to second officers to the various functions and departments within NPOIU, not just in the area of undercover policing. It would not be appropriate to discuss particular officers or postings but we remain committed to supporting the Pitchford Inquiry where appropriate."

A National Police Chiefs Council spokesman said: “The police service is committed to being open and honest with the Undercover Policing Inquiry because it is an opportunity for us to learn from any mistakes made in the past and to make any changes that ensure that the public can have even more confidence in the way this vital tactic is used, managed, authorised and overseen."

“While we are doing everything we can to fully support and provide access to the Inquiry, wherever necessary and in line with the orders of the inquiry we will make applications for anonymity because it is essential that we do all we can to protect the identities of the officers and staff who volunteer for this dangerous and psychologically challenging role.”