| Tring Market Auctions Limited | Professional & scientific | 1992 |
| Trinity (Estates) Property Management Limited | Households | 1999 |
| Trinity Brook at Whetstone Management Company Limited | Households | 2014 |
| Trinity Gate Commercial Management Ltd | Real estate | 2026 |
| Trinity Land & Investments NO.3 Limited | Households | 2006 |
| Trinity Land & Investments NO.4 Limited | Households | 2006 |
| Trinity Land & Investments NO.5 Limited | Households | 2006 |
| Trinity Land & Investments NO.6 Limited | Households | 2006 |
| Trinity Land and Investments Limited | Households | 2000 |
| Trinity London Limited | Other services | 1992 |
| Trinity Nominees (1) Limited | Households | 2009 |
| Trinity Orchestra Productions Ltd | Arts & recreation | 2023 |
| Trinity P3 UK Limited | Professional & scientific | 2019 |
| Trinity Property Group Limited | Households | 2004 |
| Triple a Recruitment Ltd | Administrative & support | 2024 |
| Triple D Scaffolding Limited | Construction | 2019 |
| Triple M Services Ltd | Transport & logistics | 2020 |
| Triple W (Watson) Limited | Public administration | 2024 |
| Tripleclick Ltd | Information & communication | 2019 |
| Triplenine Consulting Limited | Information & communication | 2014 |
| Trips 'N' Treats Limited | Health & social care | 2006 |
| Trivanta Ventures Ltd | Real estate | 2025 |
| TRJ Facilities Ltd | Administrative & support | 2025 |
| Trucklynx Ltd | Transport & logistics | 2026 |
| True Blue Recruitment Ltd | Administrative & support | 2025 |
| True CUT Carpentry Ltd | Manufacturing | 2023 |
| True Flame GAS Services Limited | Construction | 2003 |
| Truevie Ltd | Wholesale & retail | 2020 |
| Trumpington (Phase 6 & 7) Management Company Limited | Households | 2015 |
| Trumpington (Phase 8-11) Management Company Limited | Households | 2015 |
| Trumpington Meadows Residents Management Company Limited | Households | 2012 |
| Trust Invest Property Ltd | Real estate | 2025 |
| Trusted Estates Limited | Administrative & support | 2011 |
| Trusted Healthcare Services Ltd | Health & social care | 2025 |
| Trustist Innovation S Ltd. | Manufacturing | 2025 |
| Trustmark Roofing & Driveways Ltd | Construction | 2025 |
| TS Rental Properties Ltd | Extraterritorial | 2024 |
| TS Trade Solutions Limited | Hospitality | 2022 |
| TSA Homecare Ltd | Health & social care | 2018 |
| Tsaik Ltd | Construction | 2026 |
| Tsalach Tech Ltd | Information & communication | 2017 |
| TSE Productions Ltd | Administrative & support | 2017 |
| Tsitsos Ltd | Hospitality | 2026 |
| TTC Advisors Ltd | Administrative & support | 2016 |
| Tucker French EOT Ltd | Financial services | 2025 |
| Tucker French Limited | Wholesale & retail | 2000 |
| Tucker French Properties Ltd | Administrative & support | 2014 |
| Tudor Boier Limited | Transport & logistics | 2017 |
| Tudor Mortgages Limited | Financial services | 2014 |
| Tuftox Ltd | Wholesale & retail | 2025 |
| Tugyar Limited | Transport & logistics | 2024 |
| Tunetech Hemel Hempstead Limited | Wholesale & retail | 2017 |
| Tunetech Limited | Wholesale & retail | 2011 |
| Turing Intelligence Technology Services Ltd | Information & communication | 2023 |
| Turkish Barber Hemel Ltd | Other services | 2022 |
| Turkish Kebab 29 Ltd | Hospitality | 2026 |
| Turner & Turner Property Investment Limited | Real estate | 2026 |
| Turner Mechatronics Ltd | Wholesale & retail | 2017 |
| Turner Performance & Diagnostics Limited | Wholesale & retail | 2013 |
| Turquet Ltd | Manufacturing | 2021 |
| Turtle Media Ltd | Administrative & support | 2025 |
| Turtle Tops Swim School Ltd | Arts & recreation | 2021 |
| Tuskvale Limited | Households | 1985 |
| TVM Norwich Limited | Administrative & support | 2021 |
| TVR Controls Inc. Limited | Construction | 2012 |
| Tweaks Beauty and Aesthetics Ltd | Other services | 2023 |
| Twenty One Thorold Road Management Company Ltd | Households | 2010 |
| Twenty Twenty Shots Ltd | Hospitality | 2020 |
| TWENTY2 ANA Beauty Services Ltd | Other services | 2023 |
| TWENTY4 Holdings Ltd | Other services | 2015 |
| TWENTY8TWELVE London Limited | Wholesale & retail | 2012 |
| TWENTYFIVE90 Ltd | Financial services | 2019 |
| Twin Computer Services Limited | Information & communication | 1994 |
| Twin Property Holdings Ltd | Real estate | 2026 |
| Twine Carpentry & Joinery Ltd | Manufacturing | 2024 |
| Twinfinity Construction Ltd | Construction | 2013 |
| Twink Apparel Ltd | Administrative & support | 2016 |
| Twink Limited | Administrative & support | 2018 |
| Twinmar Chester Ltd | Real estate | 2024 |
| Twinmar Group Limited | Financial services | 2016 |
| Twinmar Investments Holdings Limited | Financial services | 2016 |
| Twinmar London Limited | Wholesale & retail | 2020 |
| Twinmar Sutton Ltd | Real estate | 2024 |
| Twinmar Tech Limited | Wholesale & retail | 1973 |
| Twins Hair and Beauty Limited | Other services | 2014 |
| TWM Property Ltd | Construction | 2024 |
| TY Gwyn Enderby Limited | Real estate | 2020 |
| TY Newydd Management Company (Wrexham) Limited | Households | 2007 |
| Tyche Consultancy Ltd | Administrative & support | 2024 |
| Tyeo Limited | Information & communication | 2010 |
| Tyldesley Square (Tyldesley) Management Company Limited | Households | 2006 |
| Tyler Griffen Limited | Administrative & support | 2022 |
| Typecast Design Limited | Professional & scientific | 2008 |
| Typematic Limited | Administrative & support | 2007 |
| Typetrade Limited | Administrative & support | 2003 |
| U&Nk Homes Ltd | Real estate | 2026 |
| U-Fit Window Systems Limited | Manufacturing | 1986 |
| U-Nik Line Ltd | Construction | 2014 |
| UB Holdco Ltd | Administrative & support | 2024 |
| Uber Glamorous Ltd | Wholesale & retail | 2024 |