| 3D Cadcea Ltd | Surrey |
| 3D Computer Services | Ards and North Down |
| 3D Scanners UK Ltd | West Midlands |
| 3D Visual World | |
| 3D Web Technologies Ltd | Greater Manchester |
| 3D-Verso | |
| 3DEO NI Ltd | |
| 3DNovations | |
| 3DPixel.uk | Northamptonshire |
| 3EN Group Ltd | |
| 3Es IT Ltd | West Yorkshire |
| 3Ge-solutions | Greater London |
| 3i Group plc | |
| 3i Studio Ltd | |
| 3internet Ltd | Hertfordshire |
| 3k Design | Tyne and Wear |
| 3Legs.com | Isle of Man |
| 3local Ltd | |
| 3M United Kingdom plc | |
| 3mil Ltd | Greater London |
| 3P Innovation | Warwickshire |
| 3radical | |
| 3rd Light Media | Buckinghamshire |
| 3rd Planet Connections Ltd | Dorset |
| 3rd Rock Design | Greater Manchester |
| 3S Money Club Ltd | |
| 3SIX5 Digital | |
| 3sixty | Bristol |
| 3Squared Ltd | South Yorkshire |
| 3tc Software | Leicestershire |
| 3wBiz | |
| 3wise Digital | Surrey |
| 4 Day Week | |
| 4 Earth Intelligence | |
| 4 Medical Clinical Solutions | |
| 4 Site Security | |
| 4-wardloop Design | East Sussex |
| 42Genetics | |
| 44 Web Design | West Midlands |
| 499Designs | Greater Manchester |
| 49th Floor Design & Artworking | |
| 4basebio plc | |
| 4C Creatives | South Yorkshire |
| 4C Strategies Ltd | Leicestershire |
| 4CBiomed Ltd | |
| 4CM | |
| 4Com plc | Dorset |
| 4D Digital Ltd | |
| 4D Medicine Ltd | |
| 4D Solutions Ltd | Buckinghamshire |