In a statement, the National Australia Bank (NAB) said: “The theft is covered by self-insurance, and as such, National Australia Bank will bear the impact of any losses arising from the theft.”

Police have confirmed that more than £22m ($A55.58m) was stolen from the Northern Bank in Belfast.

The haul finishes a year in which NAB discovered it had lost A$360 million in a rogue trader’s scandal.

A former NAB dealer has been charged by Australia’s securities regulator ASIC in relation to the currency options trading scandal.

Former senior trader, David Bullen, has confirmed he faces 20 charges, including one under the Crimes Act, of obtaining financial advantage by deception.

“What did the Queen say a few years ago? This has been an annus horribilis,” an unnamed official with NAB Europe said.

NAB said the robbery of the Belfast bank would have no knock-on effect for the sale of the Northern to the Danish Danske Bank Group announced earlier this month.

It also said customers would not be affected.

While a date for the sale has not been finalised, Danske chief financial officer Tony Thierry Andersen said the robbery would not affect the A$3.27b it had offered.

More than 45 detectives are working on the case in which gang members posed as police officers and held the families of two bank workers hostage for 24 hours.

Detectives are studying earlier robberies staged by paramilitaries and are seriously pursuing theories that the largest cash theft in British history has been carried out by a group such as the IRA.

Bill Lowry, the former head of Northern Ireland’s police anti-terrorist squad, said the robbery was “a well organised, well executed operation carried out with military precision, with 20 people or more probably involved”.

“The best organised crime gangs in Ireland are the paras (paramilitaries), and the Provisional IRA has the capacity more than any other of carrying out this type of crime and dealing with 20 million or 30 million pounds,” he said.

The provisional wing of the Irish Republican Army (IRA) is the biggest Catholic paramilitary group.

It is observing a ceasefire in its armed struggle against British rule, but is resisting pressure to give up its weapons and disband in the wake of a 1998 peace accord.

The actual robbery may have been well-executed but the gang may be foiled by their distinctive haul.

Of the £22m, £12m is in new Northern Ireland £10 and £20 banknotes which are rarely accepted even elsewhere in the United Kingdom, let alone anywhere else in the world.

Detective Superintendent Andy Sproule said £1.15m ($A2.91m) is in new £100 and £50 notes, while more than £5m is in assorted used Northern Ireland notes.

The rest is in British pounds and euros.