Reece Theison (20), of no fixed address, pleaded guilty to three charges when he appeared at Nottingham Crown Court on Tuesday. He will be sentenced on Friday.
The ten-hour siege happened at the Spot-On snooker and leisure club on Vine Terrace, off High Street, on Thursday 13th March.
The court heard that, after a report by a firearms expert, it had been established that Theison was armed with an imitation pistol, rather than a real Dan Weston gun, as originally thought.
It was also said that he “made no apparent intent to discharge the weapon”.
Theison admitted possession of a gas-powered air-pistol, constructed in the style of a Smith And Wesson revolver, that caused a police officer, Pc Lee Colopy, to believe that unlawful violence would be used against him.
He also pleaded guilty to stealing alcohol and food from the Spot-On club and to damaging fixtures and fittings at the club.
A 25-page psychiatric report on Theison was presented to His Honour Judge Stuart Rafferty.
The court was told that the “comprehensive” report contained sufficient information without the need for the probation service to prepare a pre-sentence report as well.
Judge Rafferty said the case had attracted “some notoriety”. However, he adjourned the hearing until (Friday) after John Fountain (prosecuting) disclosed that two important victim-impact statements were not yet available.
These statements were from two members of staff at Spot-On, Kerry Moran and Patricia Lancaster, who were trapped in the building at the time of the siege.
“They were in an office at the club for six and-a-half hours, although Theison did not know they were there,” said Mr Fountain.
Judge Rafferty adjourned the hearing so that “the statements could be obtained if at all possible”.
Hucknall town centre went into lockdown during the siege, which received publicity across the country.
Streets were blocked off, shops were forced to close early and residents were refused access to their homes.
As armed officers surrounded the club, the siege went on from 2.20pm until the early hours of the following day.