"Just a little bit pleased with yourself, ain't ya? And rightly so, rightly so. You're on the way to being a big face in this filthy cesspit. You've done me a few favors, so I am going do you a very big favor. You're with me now and the Crisp Twins are getting on a bit. In a few years I'll be takin over the whole bread basket. And if you've got that special something, you can too. Now stop loafin around and get to work."
Jack appears in GTA London 1961 as a minor character during a mission for Harold Cartwright. He gives the player information about some small street gangs in southern London, whom the player has to eliminate. After that he is not seen in the game anymore.
Jack first appears after the player does some jobs for Harold. He wants the player to meet him in his house in Mile End, where he tells him that he plans on being a big crime lord of London, and he can make the protagonist an important person too, but first he needs to work. Parkinson's jobs involve eliminating rival outfits, taking protection money, killing Filthy Colin, killing a career man and obtaining a money filled S-Cart, stealing crown jewels, stealing used money bills, kidnapping Germans in a Double Decker, kidnapping an important man who has been a threat to Albert Crisp and taking the ransom money for him, stealing a Copper for a job, blowing up a truck in the middle of an intersection and delivering carpets made out of rhinoceros skin to the Crips twins. Jack will then tell you to meet with the Crisp twins and after that you start working for them. He is not seen after that anymore and it's assumed that he took over most of the London Mob's actions after the Crisp twins' wipeout.
Jack Parkinson's image is inspired by that of a real-life British style icon, singer and actor David Bowie; albeit Parkinson is much younger than Bowie was when the game came out in 1999. Bowie's career was starting out at the same time the game is set, during the late 1960s, when Bowie looked alike to Parkinson's image.