British Prime Minister Margaret Thatcher considered banning the vote from Irish citizens living in the UK.
She told Northern Ireland Secretary Humphrey Atkins she did not believe there was hostility between the Irish Republic and the IRA during a tense meeting at Downing Street on August 23, 1979.
She said the only way to bring the Irish Government into line on security was to think about imposing restrictions against Irish people living in the UK.
Meanwhile, a snapshot of the tension between Britain and the US over the supply of guns to the police in the North was disclosed in the State papers.
Mrs Thatcher pulled no punches in her dealings with US President Jimmy Carter after the US government refused to grant an export licence for Ruger revolvers intended for use by the RUC in July 1979.
A note of a discussion between Mrs Thatcher and Mr Atkins on August 23, 1979, reveals her attitude: "She was not in the habit of discussing the internal problems of the US with the Americans and they should not attempt to do so with us.
"The Americans must be made to realise that for so long as they continued to finance terrorism, they would be responsible for the deaths of US citizens (as had happened in the Hilton Hotel explosion in Belfast) as well as others."
Despite British anger, Mr Carter remained firm on the arms ban.