| Juno Capital | |
| Juno Computers | |
| Juno Computers Ltd | |
| Juno Media | Nottinghamshire |
| Juno Telecoms | |
| Juno Web Design | |
| Jupitrr AI | |
| Juro | Greater London |
| Just Add Tech Ltd | |
| Just Add Water (Development) Ltd | |
| Just After Midnight | Greater London |
| Just Applications Ltd | |
| Just Develop It | |
| Just Eat | |
| Just Internet Solutions | Greater Manchester |
| Just Say Net | |
| Just Servers | Norfolk |
| Just Software Solutions | Cornwall |
| Just Space | Somerset |
| Just Structure | |
| Just Think I.T. | Cambridgeshire |
| JustCall | |
| JustCloud | |
| Justin March | Gloucestershire |
| Justin Wanstall | East Sussex |
| Justin Woodford | West Sussex |
| JustInspired | |
| Justo Software Ltd | |
| JustTotalTech | |
| Juvanescence Design | Neath Port Talbot |
| Juvenate Media Ltd | Gloucestershire |
| JUXT Ltd | Buckinghamshire |
| JVM Solutions Ltd | |
| JWP Computer Services Ltd | Derbyshire |
| K Consultancy | |
| K. Lacey | West Sussex |
| K3 | Greater Manchester |
| K3 IBS | Greater Manchester |
| KaarbonTech | |
| Kadence Bio | |
| Kadmos Capital Ltd | |
| Kagool | Cardiff |
| Kahootz | |
| Kaiasm Ltd | |
| Kainos | |
| Kaizan | |
| Kaizen Systems Ltd | Berkshire |
| Kalexiko Ltd | |
| Kalibrate Technologies Ltd | |
| Kalidescope Ltd | Shropshire |