Ireland was given a "back-door bailout" worth around £10 billion (€11.5 billion) by Britain in "an arrangement that was never explicitly approved by parliament", according to a report today.
The London Times claims Ulster Bank has accounted for about a quarter of losses since 2008 at the state-owned Royal Bank of Scotland, which is 81 per cent owned by British taxpayers after a £45 billion state bailout five years ago.
Quarterly reports after the Irish property market collapsed in 2010 show losses at Ulster Bank amounted to £10 billion, exceeding those in the rest of the RBS group combined.
The money pumped into Ulster Bank is more than three times the £3.25 billion direct loan offered by the British government to Ireland in 2010, which was approved by parliament after a heated debate and vote.
The future of Ulster Bank, and whether it should be separated from the rest of RBS, is to be discussed by the Parliamentary Banking Standards Commission in the UK this week.