| THE Window Film Company UK Limited | Construction | 1998 |
| THE Woodman Partnership Ltd | Real estate | 2009 |
| THE Woof Cottage Ltd | Other services | 2025 |
| THE Woof Pack Chelsea Ltd | Other services | 2025 |
| THE Writers' Guild of Great Britain Trustee Company Limited | Arts & recreation | 2011 |
| Thine Construction Limited | Professional & scientific | 2024 |
| Think Perfect Ltd | Wholesale & retail | 2019 |
| Think Perfect Solutions Limited | Real estate | 2021 |
| Third EYE Games Ltd | Information & communication | 2018 |
| Thirkettle Asset Management Limited | Financial services | 2012 |
| Thirkettle Group Limited | Financial services | 2012 |
| Thms Services Ltd | Construction | 2017 |
| Thordis Systems and Media Ltd | Information & communication | 2024 |
| Thorne Technologies Ltd | Information & communication | 2014 |
| Thornmead Financial Ltd | Professional & scientific | 2023 |
| Thread & INK Design Studio Ltd | Professional & scientific | 2025 |
| Three Rivers Property Investments Limited | Real estate | 1984 |
| Three Traders Limited | Wholesale & retail | 2025 |
| Thrive AS Leaders Ltd | Professional & scientific | 2021 |
| Thrive Organisational Consulting Ltd | Professional & scientific | 2023 |
| Tiberiu Varga Limited | Health & social care | 2015 |
| Tiger Kitchen London Limited | Hospitality | 2025 |
| Tilelogic Ltd | Wholesale & retail | 2025 |
| Timothy Howard Limited | Construction | 1970 |
| Tithings Management Company Limited | Extraterritorial | 1984 |
| Tithings Properties Limited | Real estate | 2014 |
| Tivri Ltd | Wholesale & retail | 2021 |
| TJ Window Cleaners Ltd | Administrative & support | 2017 |
| TLA Medical Ltd | Education | 2022 |
| TM Motorsport Ltd | Wholesale & retail | 2021 |
| TO Refreshment Limited | Wholesale & retail | 2020 |
| Tony Brummell Civil Engineering Limited | Professional & scientific | 2010 |
| Top Dawg Studio Ltd | Wholesale & retail | 2018 |
| Top Nails 11 Ltd | Other services | 2023 |
| Top-Notch Designs Limited | Manufacturing | 1987 |
| Topchoice Selection Ltd | Real estate | 2025 |
| Topshelf Rentals Ltd | Real estate | 2024 |
| Torver Partners Ltd | Professional & scientific | 2023 |
| Touch and WIN Ltd | Information & communication | 2000 |
| Town & Country Security Systems Limited | Other services | 2008 |
| Tradkin Limited | Information & communication | 2008 |
| Trampy's Ltd | Arts & recreation | 2023 |
| Trango Properties Limited | Real estate | 2014 |
| Travel Aura Ltd | Administrative & support | 2024 |
| Travelade Limited | Administrative & support | 2026 |
| Trekkers Bars Ltd | Hospitality | 2019 |
| Trelawny Properties Limited | Construction | 2025 |
| Trifecta Talent Ltd | Administrative & support | 2023 |
| Tring Solutions Limited | Information & communication | 2014 |
| Trinity Sons Holdings Limited | Financial services | 2026 |
| Trinity Zion Ltd | Real estate | 2026 |
| Tripath Limited | Wholesale & retail | 1972 |
| Triple Eight Container Holdings Limited | Financial services | 2023 |
| Triple Eight Containers Limited | Administrative & support | 1999 |
| Trodds Limited | Energy | 2012 |
| Troy Freight Management Limited | Transport & logistics | 2024 |
| Troy Trading Consulting Ltd | Wholesale & retail | 2020 |
| Truck Masters Hub Ltd | Wholesale & retail | 2025 |
| True Colours Trading in Berkhamsted Ltd | Wholesale & retail | 2013 |
| True Stories Ltd | Professional & scientific | 2025 |
| Truth BE Gold Ltd | Other services | 2016 |
| TS Motors Engineering Limited | Wholesale & retail | 2018 |
| TSA Ventures Ltd | Wholesale & retail | 2020 |
| Tsjh Clothing Limited | Wholesale & retail | 2022 |
| TT Martial Arts Chesham Ltd | Arts & recreation | 2025 |
| TTC Financial Services Limited | Real estate | 1977 |
| Turn-Key Marketing Services Ltd | Professional & scientific | 1993 |
| Turner Construction Limited | Construction | 2016 |
| Turtle Projects Ltd | Transport & logistics | 2020 |
| Twainshourne Limited | Households | 1974 |
| Twelve Arts Limited | Manufacturing | 2014 |
| Twenty-One Bramham Gardens (Management) Limited | Households | 1994 |
| TWG Properties Ltd | Construction | 2019 |
| Two Create Studio Limited | Administrative & support | 2008 |
| Two Spoons Tea Ltd | Wholesale & retail | 2020 |
| Two Zero Design Ltd | Professional & scientific | 2018 |
| Twynham Aviation Limited | Transport & logistics | 2019 |
| TZ Partners Ltd | Professional & scientific | 2024 |
| U-Freight (UK) Limited | Transport & logistics | 1998 |
| Uchaf Fields Ltd | Agriculture & fishing | 2014 |
| UK Recruit Line Ltd | Other services | 2018 |
| UK Sniffer Dogs Limited | Other services | 2019 |
| Underfloor Heat Limited | Wholesale & retail | 2020 |
| Underground Installation Solutions Ltd | Construction | 2015 |
| Unionsons Limited | Professional & scientific | 2015 |
| United Kingdom Lubricants Association Ltd | Other services | 1968 |
| UNO MAS Culture Ltd | Manufacturing | 2020 |
| Unobtanium Limited | Construction | 2021 |
| Untoasted Productions Ltd | Information & communication | 2026 |
| Unwyre Ltd | Information & communication | 2019 |
| Upgang Lane Ltd | Professional & scientific | 2019 |
| Upper CUT of the Chalfonts Limited | Other services | 2008 |
| Uppingham Avenue (Harrow) Management Company Limited | Real estate | 2005 |
| Upriseup Limited | Administrative & support | 2011 |
| Upsafe Scaffolding Ltd | Construction | 2017 |
| Upskillbrits Ltd | Administrative & support | 2024 |
| Urban Crest Holdings Ltd | Real estate | 2026 |
| Urban Doors Limited | Manufacturing | 2006 |
| Urban Home Refurbishments Ltd | Construction | 2017 |
| US Plus AI Ltd | Information & communication | 2025 |