THERESA May repeatedly refused to extend an official inquiry into rogue undercover police to Scotland, despite SNP ministers warning she was doing their victims a “disservice”.

Correspondence released under Freedom of Information has revealed escalating tension between the Scottish and UK governments over the probe into officer misconduct.

Despite rogue cops routinely spying on people in Scotland, as Home Secretary Mrs May refused to extend the inquiry’s remit, which she set, beyond activity in England and Wales.

Expressing his “disappointment”, Mr Matheson told her bluntly: “The narrower approach you are currently pursuing risks doing a disservice to people in Scotland affected by the activities of a force falling under the oversight of your department.”

Mrs May set up the inquiry in 2014 after revelations undercover police infiltrated political and environmental groups and had sex with some of the female protesters they were spying on.

Officers often faked mental illness to disappear suddenly from long-term relationships.

Spies also collected information about grieving families, including the parents of the murdered teenager Stephen Lawrence, and stole the identities of dead children.

Police in Scotland were seconded to a disgraced undercover unit called the National Public Order Intelligence Unit (NPOIU), which was set up to 1999 to combat domestic extremism, but extended its surveillance to low-level protest campaigns.

Although based south of the border, NPOIU operated in Scotland, embedding officers such as the notorious “Mark Stone” – also known as Mark Kennedy – into groups at the G8 summit in Gleneagles in 2005

Originally known as the Pitchford Inquiry, the investigation is now known as the Undercover Policing Inquiry since the judge leading it stepped aside for health reasons.

The correspondence, released by the Scottish Government, shows SNP Justice Secretary asked Mrs May in multiple phone calls and letters to extend the inquiry to Scotland.

After he wrote to Mrs May in December 2015, she replied the following month, saying the inquiry was “interested in the whole story” and “a complete picture”, but went on: “I am not minded to expand the terms of reference at this time, but I am happy to discuss further.”

The pair then had a telephone conversation on February 2 in which Mrs May agreed to look at whether the inquiry could “consider specific incidents where Metropolitan Police officers have been involved in national operations in Scotland”.

But in March she wrote that “after careful consideration” she was still “not minded to revisit the scope at this stage given the impact of doing so. I must therefore advise you that, regrettably, the inquiry will not be able to consider activities in Scotland.”

However later that month Mr Matheson persisted and expressed his “disappointment”.

He said: “There is a great deal of Scottish interest in understanding the full story of how the Metropolitan Police may have operated in Scotland, and it is my understanding that a number of individuals are already providing Lord Pitchford’s Inquiry with information that relates to MPS activities in Scotland.

“I therefore remain of the view that the best course of action would be to extend the remit to cover MPS activities in Scotland.”

But in a third letter, in April 2016, Mrs May again refused to budge, telling Mr Matheson: “The Chairman of the Inquiry… will not be able to make any conclusions or findings with regard to activities in Scotland even if such evidence is submitted. Any evidence which relates to activity outside England and Wales is beyond the inquiry’s terms of reference.”

Mr Matheson tried again the following month, saying he supported an idea from the then Northern Ireland Justice Minister, David Ford, that the Inquiry be empowered to consider any evidence where an operation in England and Wales “crossed a jurisdictional boundary”.

After Mrs May became Prime Minister in July last year, correspondence on the issue was picked up by Tory Policing Minister Brandon Lewis.

He told Mr Matheson the new Home Secretary, Amber Rudd, was also refusing to extend the remit of the inquiry as it was “extensive and complex, with around 200 core participants”.

He explained: “Amending the terms of reference at this stage would require further consultation and delay the progress of the inquiry.

“In the interests of learning lessons from past failures and improving public confidence it is important that the inquiry proceed swiftly and make recommendations as soon as possible.”

The inquiry, now chaired by Lord Mitting, has so far cost around £7m.

It was due to be completed next year, but is now thought unlikely to start hearing evidence in public until the second half of 2019.