| 2Magpies | Greater Manchester |
| 2mee Ltd | |
| 2ndQuadrant Ltd | Oxfordshire |
| 2SEETV Ltd | Lancashire |
| 2sms | Nottinghamshire |
| 2x Consulting Ltd | Oxfordshire |
| 3 Sided Cube | Dorset |
| 3 Tier Systems Ltd | |
| 32Co. Ltd | |
| 34SP.com | Greater Manchester |
| 350 PPM Ltd | |
| 360 Digital | |
| 360 Spin Ltd | |
| 360fusion Ltd | North Yorkshire |
| 360innovate | Glasgow |
| 360ss | Kent |
| 365 Response | |
| 365 Techies Ltd | |
| 365IT | Berkshire |
| 3aIT Ltd | West Sussex |
| 3ami Ltd | Lancashire |
| 3B Systems Ltd | Lancashire |
| 3C Technology | Essex |
| 3chillies | Berkshire |
| 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 |
| 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 |
| 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 | |
| 3sixty | Bristol |
| 3Squared Ltd | South Yorkshire |