Irish President Patrick Hillery’s decision to decline an invitation to the wedding of Charles and Diana prompted concerns from Irish government officials.

The invitation was sent to Mr Hillery and his wife for the wedding on July 29 1981 in St Paul’s Cathedral, and requested a reply by June 26.

A briefing note on how to respond to the invite is among the State documents released by the Department of Foreign Affairs to the National Archives this year.

It asked whether the reply should be issued after the Irish general election, or would it be “discourteous” to do so, while also noting that sending a reply too soon after the invite could also be “discourteous”.

The note also ponders that since it is a “negative” reply, “it would seem desirable to offer a diplomatic excuse”, as no decent reason being given could be “misinterpreted both domestically and internationally”.

“The press will certainly ask the reason for the non-attendance.”

The document also weighed up the pros and cons of attending the wedding, noting that an invite from a “friendly” country to an occasion “such as this” should be accepted, but adding that the Irish President would attract “unfavourable” comment if he did attend.

The wedding invitations were issued a month after IRA prisoner Bobby Sands died after a 66-day-long hunger strike, as part of a campaign to be treated as a political prisoner.

“The present state of Anglo-Irish relations, and specifically the very general feeling of dissatisfaction in both the north and the south with the British Government’s policy on prison conditions in Northern Ireland would ensure that there would be much unfavourable comment if the President were to attend the royal wedding,” the document said.

It added that with the “appropriate diplomatic excuse”, a refusal of the Irish President’s attendance would not “impair the political dialogue with London”.

On June 26 1981, the final date by which the RSVP was to be given, Ireland’s Ambassador to the UK conveyed the Irish President’s thanks for the wedding invite but expressed “their regret that, because of prior commitments, they will be unable to attend”.

“They have instructed that the ambassador should represent them on this occasion,” it added.

The material can be viewed in the National Archives in file 2023/47/2319