Jimmy Duncan was the main antagonist of the Sun Hill Siege storyline of the British TV series The Bill.
Assault on Sun Hill introduced the new fictional character of Detective Sergeant Max Carter, with it being DS Carter's first day at Sun Hill CID when the siege takes place. Meanwhile, Detective Constable Terry Perkins receives information of a planned robbery from an informant, while Constables Benjamin Gayle and Sally Armstrong are called to a disturbance over unpaid taxi fares. Tiff and Paula, the females involved in the disturbance are later arrested and held in the custody suite. DC Perkins also makes arrests of the would be robbers he had information about, but also finds his informant shot and bleeding to death who dies in DC Perkins arms. To alleviate the stress, DC Perkins drinks while on duty and ends up heavily intoxicated, being found by a fellow officer and unofficially placed in a cell to sober up by a fellow officer.
Constables Tony Stamp, Ben Gayle and Sally Armstrong are in the process of formally releasing Tiff and Paula when two men rush into the front office taking Sally and Tony hostage.
The two men who rushed into the front office were both wearing masks and were armed, threatening PC Stamp with death unless he shows them to the cells where Tiff and Paula are being held. Outside the station and unaware of events inside, Sergeant Callum Stone radios the number plate to be run through the Police National Computer, only to find that it was reported as stolen. CO19 armed officers who are walking into the station by coincidence clearly see PC Armstrong held at gunpoint, resulting in a CO19 officer shot.
Upon learning their boyfriends have stormed into the station attempting to free them from police custody, they are both stunned. Jimmy Duncan, the would-be robber DC Perkins arrested, helps the hostage takers control the siege, with the reasoning that they are "amateurs".
Upon learning of the siege, Inspector Gina Gold requisitions a pub as an observation and control point. Inside the station, PC Gayle realises that Tiff has swallowed a drug filled condom and it is leaking causing her to slowly overdose.
With the help of experienced criminal, Jimmy Duncan, the hostage takers have moved the officers into the Integrated Borough Operations suite, the nerve centre of the station where CCTV can be observed of all the entry and exit points. The hostage takers also issue demands, stating they want a bus with a driver so they can escape with their hostages. While Tiff and Paula are in the toilet, Sally tried to convince them to persuade their boyfriends to end the siege. Meanwhile, Jimmy Duncan murders one of the hostage takers. DC Perkins wakes up in his cell and walks straight into Jimmy Duncan with Perkins managing to pass himself off as a criminal rather than police officer. To convince Jimmy, DC Perkins sets fire to the canteen, but unknown to Terry, Jimmy had seen his warrant card. As the fire takes hold, both hostage takers and hostages scramble through the front entrance. Terry and PC Will Fletcher pursue Jimmy Duncan, with Terry about to shoot him when DI Samantha Nixon arrives with armed officers.