Using Irish for official business in Northern Ireland could lead to "rabidly" polarised communities, British Government files from 1987 said.
The Northern Ireland Office (NIO) warned against sentimentalising the value of the language and culture in a confidential briefing note between officials.
In recent years Irish language publications have been routinely produced by some Stormont departments.
Dublin ministers made demands surrounding the adoption of dual languages and the protection of Irish cultural identity following the Anglo-Irish Agreement (AIA), records suggested.
But a NIO official said: "The conventional pluralism of Northern Ireland public policy will be shattered and we shall end up with two rabidly British and rabidly Irish communities ... I see no reason to believe that there is any route to internal harmony which does not involve wider, indeed post-national identities."
NIO officials said the views of the Republic could not help but be reactionary.
"Because Irish nationalism is reactionary, Ulster nationalism is doubly reactionary.
"It is only the UK which is in a position to take a properly comprehensive view and it really cannot do so if we sentimentalise about the value of Irish language and culture.
"The reality - and a very good thing too - is that Ireland and Britain are both sharers in mid-Atlantic society.
"It is always possible for the Robin Flowers (an English poet who translated poetry from Irish) of this world to love romantic Ireland dead and gone. But it would be disastrous if that spirit played any part in UK public policy-making.
"Happy New Year (as we say in London, Edinburgh, Cardiff, Dublin and Belfast)."
After Stormont's power-sharing Executive was established in 1999 some devolved departments began using Irish.
A Language Act is a key outstanding demand of Sinn Fein to protect a minority tongue which it argues belongs to all. Senior Democratic Unionist Nelson McCausland has claimed Irish is a weapon in Sinn Fein's cultural war.
Ulster Unionist Regional Development Minister Danny Kennedy has decided not to add Ulster Scots and Irish to some road signs.