Gavin Geddes, 46, of Vale Avenue, Brighton, was sentenced to 40 months in prison at Lewes Crown Court on Friday (February 1) following an earlier three-day trial.
Sussex Police said: "Officers were contacted by the victim, an 85-year-old man from Hove, in August 2017 to report a matter of blackmail.
"The victim said over the previous five months he had been sent threatening letters from Geddes that stated if he didn’t pay the required amount, Geddes would say he was sexually assaulted by the victim.
"Through fear of having his reputation tarnished, the vulnerable victim paid Geddes £47,000 in four separate transactions. Despite the bank being concerned by the figure of money being transferred to Geddes, the victim convinced staff he was not being blackmailed and the payments were legitimate.
"In August 2017 the victim received another letter from Geddes of similar content to the previous ones. At this point, the victim had no savings left and decided contacted the police for support.
"Geddes, a van delivery driver, was arrested by officer on August 11, 2017 but later released under investigation.
"Officers launched a complex investigation into the case and the evidence collated allowed Geddes to be charged and convicted."
Detective Constable Tom Coll said: “Geddes saw an opportunity to exploit an elderly victim for his own personal gain by preying on his desire to maintain his reputation and status in society.
“I hope the guilty verdict and custodial sentence Geddes received sends a clear message that blackmail is a serious offence.
“We would encourage anyone who is a victim of blackmail to make contact with us to ensure the matter is inve