| Fireproof Games | |
| Firesprite Ltd | |
| Firestartr | |
| Firestoke Group Ltd | |
| Fireteam Ltd | |
| FireText Communications Ltd | Cornwall |
| Fireworx ICE Ltd | |
| Firms Online | South Yorkshire |
| First 4 IT Ltd | North Yorkshire |
| First Choice Assembly Ltd | West Midlands |
| First Class Technologies Ltd | |
| First Derivatives plc | Newry, Mourne and Down |
| First Internet Ltd | |
| First Light Fusion Ltd | |
| First Line Support Ltd | Oxfordshire |
| First Option Software | Hampshire |
| First Option Technical Support Ltd | Hampshire |
| First Payment Merchant Services Ltd | |
| First Rental | Bedfordshire |
| First Stop IT Ltd | Essex |
| First Stop Web Design | |
| First4tech Ltd | Devon |
| Firstco | |
| Firstcom Europe | Oxfordshire |
| FirstFound | Greater Manchester |
| Firstminute Capital | |
| FirstRank Group Ltd | |
| FirstServ Ltd | Cheshire |
| Firsty Group | Berkshire |
| FIS Chemicals | |
| FISC Ltd | South Yorkshire |
| Fish Media | Derbyshire |
| Fish4Jobs Ltd | |
| Fisheye | Shropshire |
| Fisheyes Ltd | Renfrewshire |
| Fishtank | West Yorkshire |
| FIT | |
| Fitech UK Ltd | Greater London |
| Fitness Metaverse | |
| FiTR | |
| FITSystems Ltd | East Sussex |
| Fivani | |
| Five Alarm Bio Ltd | |
| Five by Five Global | Hampshire |
| Five Rivers | West Midlands |
| FiveAI Ltd | Cambridgeshire |
| Fivenines | |
| Fiverivers Ltd | |
| Fix Computers | |
| Fix-My-PC.net | South Yorkshire |