The NIO viewed it as significant that Peter Robinson kept raising the possibility of Northern Ireland becoming independent - even though he insisted that he opposed such a possibility, declassified government files show.
Over recent years as files from the post-Anglo-Irish Agreement period have been released, the DUP deputy leader has emerged as someone who was raising the issue, although never arguing for it.
In 1986, the year after the agreement was signed and in a period of deep unionist dismay, Mr Robinson told NIO official Danny McNeill that “increasingly people in the Protestant community were focusing on independence”.
Mr McNeill recorded that “he said that he did not advocate that - though I was not entirely convinced - but that if any serious and credible politician were to so advocate then the independence movement would develop very quickly”.
In files from 1991 which have just been released at the Public Record Office in Belfast, Mr Robinson’s speech to the 1991 DUP conference was analysed.
In the speech, the then East Belfast MP told the December DUP conference: “This party believes that an independent Ulster is not an alternative to the Union.
“However, it firmly contends that an independent Ulster is an alternative to a united Ireland or to a mutation between Dublin rule and direct rule.
“The task for unionists is to establish whether the Union can be preserved on an acceptable basis.”
Mr Robinson contended that his speech should not be seen as advocating an end to the Union, but that “at the same time, it requires unionists, if they determine that the Union cannot be preserved, to become masters of their own destiny”.
In a confidential assessment of Mr Robinson’s speech, Jacqueline Black in the NIO’s political affairs division noted that “once again, Peter Robinson refers to independence - and while saying that it is not an alternative to the Union, nevertheless gets that option on the agenda”.