Ireland has paid the UK €186m (£148m) in interest payments following a crisis loan in 2010.
A total of €4bn (£3.2bn) was lent to the Republic as part of an international rescue package of the country’s collapsing economy.
A report from the UK Treasury said it will be March 2021 before the bilateral loan’s term is up. The final tranche of money was paid to Ireland a year ago.
The document said: “The Government agreed to provide a bilateral loan to Ireland because it is in the UK’s national interest that Ireland has a successful economy and a stable banking system.
“The links between our financial systems, particularly in Northern Ireland, mean that there was a strong economic case to provide financial assistance to Ireland.
“By being part of the international financial package, the UK indirectly supported the very many businesses across the UK that trade with Ireland.”
The loan was made at the same time as a bailout by the European Commission, International Monetary Fund and European Central Bank.
The Republic is one of the UK’s main export markets – at the time the loan was given it accounted for 5% of Britain’s total exports and two-fifths of exports from the North.
In late 2010 the Royal Bank of Scotland lent billions in the North - loans which were insured by British taxpayers as RBS is a semi-nationalised bank. If the Irish economy failed, that would have generated large losses for RBS and the UK taxpayer.