Former Taoiseach (Irish Prime Minister) Bertie Ahern told British MPs a border poll now "or in the foreseeable future" would be the wrong thing to do.
Mr Ahern also said Irish people believed a hard border was inevitable if there was a no-deal Brexit, despite assurances from the British and Irish governments and the EU.
The former Fianna Fáil politician was speaking at the Exiting the EU committee at Westminster.