Thatcher: Giving Dublin joint rule over Northern Ireland 'out of the question'
Margaret Thatcher said there was "no question" of agreeing to give Dublin joint authority over the running of Northern Ireland, official files reveal.
The former prime minister told unionist leaders that the Anglo-Irish Agreement (AIA) between the British and Irish Governments did not threaten UK sovereignty.
Her intervention followed a long-running unionist campaign against the 1985 Agreement, which gave the Irish Government a consultative role in Northern Ireland for the first time.
The following year, Mrs Thatcher wrote: "It is expressly stated in the Agreement that there is no derogation from the sovereignty of the UK Government, which remains solely responsible for decisions in relation to the affairs of Northern Ireland.
"There is consequently no question of 'joint authority', nor does the Agreement in any way threaten the union; I should not have been a party to it if it did.
"On the contrary, the guarantee of successive UK governments and parliaments that the status of Northern Ireland cannot and will not be changed without the consent of a majority of the people in Northern Ireland is explicitly recognised and accepted by the Government of the Republic."
Mrs Thatcher signed the AIA with Irish taoiseach Dr Garret FitzGerald at Hillsborough in Northern Ireland.
It prompted widespread unionist protests including the collapse of the Stormont Assembly and a huge "Ulster says No" rally at Belfast City Hall led by former Ulster Unionist Party head Jim Molyneaux and DUP leader Dr Ian Paisley.
An official unionist resolution had called for the right to be governed in accordance with the principles of the UK.
In March 1986 Mrs Thatcher wrote to the leaders: "One of those principles is surely the acceptance of the sovereign authority of the UK Parliament; indeed this must be a corollary of your rejection, which I share, of any dilution of that authority."