| Synergyn Ltd | Professional & scientific | 2004 |
| Synexus Clinical Research Limited | Professional & scientific | 2005 |
| Synexus Clinical Research Midco NO 1 Limited | Professional & scientific | 2015 |
| Synexus Clinical Research Topco Limited | Professional & scientific | 2015 |
| Synexus Limited | Professional & scientific | 1999 |
| Synoptics Limited | Manufacturing | 1984 |
| Syntech Premium Limited | Information & communication | 2019 |
| Syntek Design Limited | Information & communication | 2026 |
| Synthaize Ltd | Information & communication | 2026 |
| Syntheon Limited | Professional & scientific | 2026 |
| Syntherix Limited | Professional & scientific | 2022 |
| Synthexit Health Ltd | Manufacturing | 2026 |
| Syplex Cambridge Limited | Real estate | 2025 |
| Syplex Limited | Information & communication | 2000 |
| Syracuse Intelligence Ltd | Information & communication | 2026 |
| Syrcab Ltd | Transport & logistics | 2025 |
| Syrett Capital Limited | Financial services | 2025 |
| Syrett Consultancy Limited | Information & communication | 2017 |
| Syrett Properties Limited | Real estate | 2022 |
| Sysforge Ltd | Information & communication | 2024 |
| Syskit UK Limited | Information & communication | 2022 |
| Sysology Ltd | Information & communication | 2020 |
| Sysora Health Limited | Professional & scientific | 2024 |
| System Ace Ltd | Information & communication | 2024 |
| System Connections (Cambridge) Limited | Extraterritorial | 1988 |
| System Management Consultants Ltd | Construction | 2005 |
| Systematic Digital Group Ltd | Wholesale & retail | 1987 |
| Systemised to Scale Ltd | Information & communication | 2023 |
| Systemsnet Communications (London) Ltd | Administrative & support | 2014 |
| Sysweavers Limited | Information & communication | 2012 |
| Syumon (UK) Skin Science Research Center Ltd | Wholesale & retail | 2022 |
| Syvir Technologies Ltd | Information & communication | 2022 |
| SZA Limited | Hospitality | 2025 |
| Szafranski Interiors Ltd | Manufacturing | 2019 |
| SZB93 Ltd | Manufacturing | 2025 |
| SZW Limited | Extraterritorial | 2013 |
| T & J Farnell Ltd | Professional & scientific | 2012 |
| T & J Lettings Ltd | Financial services | 2012 |
| T and W Homes Project Limited | Construction | 2026 |
| T Dama Developments Limited | Construction | 1995 |
| T E B Consultants Limited | Professional & scientific | 2015 |
| T in Motion Entertainment Ltd | Information & communication | 2018 |
| T J B Developments (Cambridge) Limited | Construction | 2013 |
| T J Garrett Ltd | Construction | 2015 |
| T Leneghan Construction Services Limited | Construction | 2016 |
| T M Management Consultants Limited | Professional & scientific | 2023 |
| T P Queally Limited | Arts & recreation | 2010 |
| T Pagram T/A Searle and Sons Ltd | Wholesale & retail | 2023 |
| T Plus Zero Ltd | Information & communication | 2025 |
| T R Building Services Ltd | Construction | 2018 |
| T R Cleaning Limited | Administrative & support | 2006 |
| T R Surfacing Limited | Construction | 2019 |
| T R Wilson Windows Doors & Fascias Ltd | Construction | 2012 |
| T REX Training Ltd | Health & social care | 2021 |
| T&Ct Limited | Health & social care | 2024 |
| T&D Ice Cream Ltd | Manufacturing | 2020 |
| T&M Pars Limited | Hospitality | 2020 |
| T&P Crocker LLP | | 2024 |
| T&Rwood Ltd | Manufacturing | 2025 |
| T&S Gibb Associates Limited | Information & communication | 2025 |
| T&S Manea Ltd | Hospitality | 2026 |
| T. Hedley Ltd | Information & communication | 2023 |
| T.& W.Hays Bros.Limited | Agriculture & fishing | 1953 |
| T.A.C.T Engineering Ltd | Manufacturing | 2018 |
| T.B Marine Electrical Engineering Co., Ltd | Manufacturing | 2024 |
| T.C. Comms Ltd. | Other services | 2008 |
| T.J.S. Mechanical Marine Ltd | Manufacturing | 2022 |
| T.L.U. Puzzles Ltd | Information & communication | 2019 |
| T2DESIGN Labs Ltd | Other services | 2012 |
| T4G Medical Limited | Manufacturing | 2021 |
| TA Consulting & Coaching Ltd | Financial services | 2025 |
| TA Horizons Limited | Professional & scientific | 2026 |
| Taaz Properties Limited | Real estate | 2026 |
| Taba Consulting Ltd | Professional & scientific | 2024 |
| Tabemono Ltd | Hospitality | 2026 |
| Tabeson Ltd | Wholesale & retail | 2020 |
| Tabitha Millett Ltd | Wholesale & retail | 2023 |
| Table and Thyme Ltd | Wholesale & retail | 2022 |
| Tablespice Limited | Professional & scientific | 2000 |
| Tablet Topco Ltd | Financial services | 2020 |
| Tabletop Supply Ltd | Wholesale & retail | 2020 |
| Tace Highways Limited | Construction | 2023 |
| Tactful Ltd. | Information & communication | 2016 |
| Tactful UK Holding Ltd | Information & communication | 2023 |
| Tadelva Ltd | Real estate | 2025 |
| Tadworth Gardens Resident Management Company Ltd | Households | 2018 |
| TAG AD Limited | Wholesale & retail | 2025 |
| TAG Brand Limited | Administrative & support | 1986 |
| TAG Consulting Limited | Agriculture & fishing | 2004 |
| Tagvkitchens Ltd | Hospitality | 2025 |
| Taicang Ubang (UK) Co., Ltd | Professional & scientific | 2016 |
| Taidian Garment Accessory Co., Ltd | Manufacturing | 2015 |
| Taikilele Global UK Limited | Information & communication | 2026 |
| Tailordrcare Limited | Health & social care | 2025 |
| Tailored Architecture Limited | Construction | 2023 |
| Tailored Stays Limited | Real estate | 2016 |
| Tailorflow AI Limited | Information & communication | 2025 |
| TAILS&TRAILS88 Ltd | Other services | 2025 |
| Taipuhua Marine Co., Ltd | Wholesale & retail | 2025 |
| Taishio Ltd | Financial services | 2021 |