The head of the civil service in 1986 privately described the “true nature” of the DUP as “frightening”, declassified government files today reveal.

Sir Ken Bloomfield made the brutal assessment of a party which he described as “menacing” and “authoritarian” in a year where the DUP was at the forefront of a united unionist opposition to the Anglo-Irish Agreement.

Although the protest was mostly peaceful, at points it became illegal and officials feared that the then DUP deputy leader, Peter Robinson, was a hardliner who could destabilise the Province.

Mr Robinson emerges from the files as a figure who was somewhat enigmatic to the Government, but who they believed to be a potentially destabilising influence on Northern Ireland.

By contrast, his current Stormont Castle colleague, Martin McGuinness, barely features in the files.

Although Mr McGuinness claims to have left the IRA in 1974, he is widely believed to have been one of the IRA’s most senior commanders in 1986, and is likely to have featured heavily in RUC files, which are not released under the 20-year rule.

An April 2, 1986 memo from Ken Bloomfield, which has been released by Belfast’s Public Record Office, lamented the possibilities of devolved government in Northern Ireland.

He said it would be “irresponsible” to return substantial political power “to those parties and individuals who now dominate our politics”.

He went on: “It is serious enough that virtually all of the leading people in all the parties have practically no experience of office.

“It is still more serious that important political elements should have such a distinctly authoritarian and menacing character.

“Ministers have had ample recent opportunity to experience at first hand the true nature of the DUP in particular.

“Not merely its political behaviour but the attitudes out of which that behaviour flows are frightening.

“Nor is it just a question of the DUP. Do we seriously entertain the possibility that (say) Mr [Seamus] Mallon and Mr [Harold] McCusker will, like the lion and the lamb, quietly lie down together? I find it very hard to believe.”

Although some of those who met government ministers spotted something of the later pragmatism which would propel Mr Robinson to become first minister, most internal government reports view him with deep suspicion or hostility.

A March 5 report by the NIO’s Political Affairs Division said: “Peter Robinson’s emergence as a hard-line leader is not encouraging.”

The government’s fascination with Mr Robinson is illustrated by the fact that reports sometimes were made about him – because he had done nothing of note.

One such report by the NIO’s Political Affairs Division in March 1986 stated: “It is of interest that after his prominence in recent weeks, Peter Robinson has remained remarkably silent and almost invisible for some days.”