On 20 December 2004, a total of £26.5 million in cash was stolen from the headquarters of Northern Bank on Donegall Square West in Belfast, Northern Ireland. Having taken family members of two bank officials hostage, an armed gang forced the workers to help them steal used and unused pound sterling banknotes. The money was loaded into a van and driven away in two trips. This was one of the largest bank robberies in the history of the United Kingdom.
The Police Service of Northern Ireland (PSNI), the Independent Monitoring Commission, the British government and the Taoiseach all claimed the Provisional Irish Republican Army (IRA) was responsible. This was denied by the IRA and by Sinn Féin. Throughout 2005, the police forces in Northern Ireland and the Republic of Ireland made arrests and carried out house searches. A sum of £2.3 million was impounded at the house of a financial adviser, Ted Cunningham, in County Cork and Phil Flynn was forced to resign as chairman of the Bank of Scotland (Ireland), because he was a director of one of Cunningham's companies. Cunningham was convicted in 2009 of money laundering, had his conviction quashed in 2012 and was convicted at retrial in 2014. Chris Ward, one of the bank officials threatened by the gang, was himself arrested in November 2005 and charged with robbery. The prosecution then offered no evidence at trial and he was released.
Northern Bank announced soon after the heist that it would replace its £10, £20, £50 and £100 notes. Alongside the murder of Robert McCartney, the robbery adversely affected the Northern Ireland peace process. It caused a hardening in the relationship between the Taoiseach Bertie Ahern and the Sinn Féin representatives Gerry Adams and Martin McGuinness. Although Cunningham and several others were eventually convicted of crimes uncovered during the investigation, nobody has ever been held directly responsible for the robbery.