28-year-old Charlie Enright, formerly of Alexandra Road, had walked into the branch on June 29 and told a cashier he had a gun and wanted money.
Although no such weapon was ever seen, the cashier raised the security screens and Enright walked out of the premise.
He returned to the bank later, where he was challenged by the manager and told police had been called.
He was arrested the next day after being identified as a regular customer at the bank.
Maidstone Crown Court heard how he had already been in the bank once that day to withdraw money.
He pleaded guilty to robbery on Monday and was jailed for 16 months.
Investigating officer Detective Constable Charlene Smith said: ‘Charlie Enright has a problem with drink and drugs but that is no excuse for committing such a serious crime.
‘Staff at the bank acted in a very calm and professional manner throughout the incident but it would have been understandable for them to have been deeply distressed given that he made mention of having a gun.
‘Enright will now spend 16 months in prison for doing something foolish while under the influence, and I hope he is able to turn his life around while serving his sentence.’