Margaret Thatcher's government created a secret blacklist of "subversive" Scottish nationalists employed by the civil service, it has emerged.

Newly-released documents reveal 35 civil servants were classed as "Scottish and Welsh nationalist extremists" in the 1980s.

They were placed on a government blacklist along with more than 1400 others, a number of whom held senior positions.

The documents also identify 25 people working within the Scotland Office as subversives linked to communist and socialist groups.

None of the blacklisted civil servants are named and it is unclear what the Thatcher administration considered extremism.

One report warns Scottish and Welsh nationalists may "present public order problems resulting from their propensity for violence", however.

The documents released by the National Archives warn "subversives" should not be posted to "key areas vulnerable to disruption".

"Departments should identify their key areas and develop procedures to ensure as far as possible that subversives are not posted there," they warn.

"It might be possible covertly to move individuals to posts where they would have less potential for disruption.

"At higher levels, one or two departments do have covert systems to enable them, if necessary, to take these problems into account before promotions are decided."

Most of the so-called subversives identified in the reports were working in junior clerical positions.

They said security and vetting procedures "had been effective in virtually excluding subversives from access to classified information."

The documents also reveal how Labour home secretary James Callaghan tried to oust far left trade union leaders in the 1960s.

Concerns about socialists in the civil service intensified in the 1980s with the growth of the Militant and Socialist Workers Party.

The reports also warn about a small number of civil servants identified as fascists.

A Cabinet Office spokeswoman said the Inter-Departmental Group on Subversion in Public Life - which compiled the reports - is "no longer in operation".

"There is no other unit conducting similar work," she added.