| Jibba Jabba | South Yorkshire |
| jidatit | |
| Jigowatt | Cambridgeshire |
| Jigsaw Design Studio | Buckinghamshire |
| Jigsaw Digital | |
| Jigsaw School Apps | |
| Jigsaw24 | Nottinghamshire |
| Jim Byrne | Glasgow |
| Jim Callender | East Sussex |
| Jim Paterson | Glasgow |
| Jim Rogers Computer Services | |
| Jiminny | |
| Jinota London Ltd | Cornwall |
| Jisc | Bristol |
| JISCMail | Tyne and Wear |
| JitBit, L.P. | Edinburgh |
| Jiva.ai Ltd | |
| JJ Solutions | Greater London |
| JK Digital Solutions | West Midlands |
| JL Services | Greater Manchester |
| JLA Computer Services Ltd | Essex |
| JM IT Services | Norfolk |
| Jmix | |
| JMJ Web Design Ltd | |
| JND Solutions Ltd | Tyne and Wear |
| JNIT Soft UK | |
| Job Protocol Labs Ltd | |
| JobCannon Ltd | |
| Joblogic | |
| jobs.ac.uk | |
| JobsinJS.com | |
| Jobtrain | Greater Manchester |
| Joe Design | South Yorkshire |
| Johan De Silva | Surrey |
| John Innes Centre | |
| John Keells Holdings plc | |
| John Wood Group plc | |
| Johnson Technical | |
| Join Ploy Ltd | |
| Join Talent | |
| Joined Apps | |
| JoinedUp Group Ltd | |
| Joint Application Development enterprises Ltd | Oxfordshire |
| Jollie Design | Glasgow |
| Jolly Good Web Ltd | |
| Jon Athill | |
| Jon Colegate Ltd | South Yorkshire |
| Jon Mackenzie Web Design | Herefordshire |
| Jonathan Parons - Resources | |
| Jools UK | Hampshire |