| Think Yeti Limited | Hospitality | 2017 |
| Thomas Faulkner and Sons Limited | Administrative & support | 1975 |
| Thomas Rowbottom Limited | Construction | 2019 |
| Thorncroft Court Management Company Limited | Households | 1994 |
| Three Counties GAS and Plumbing Limited | Construction | 2011 |
| Three Hundreds Building Limited | Construction | 2010 |
| Three Lands Consultancy Limited | Information & communication | 2025 |
| Threetwo Productions Limited | Information & communication | 2022 |
| Thrugrowth Limited | Professional & scientific | 2011 |
| Thyme for Lunch Ltd | Hospitality | 2017 |
| Tide & Tumble Ltd | Other services | 2025 |
| Tier One Ltd | Administrative & support | 2025 |
| Tigastor Limited | Transport & logistics | 1990 |
| Tilearoundtown Ltd | Professional & scientific | 2022 |
| Tilsworth Clinic Ltd | Professional & scientific | 2021 |
| Tilsworth Motors Limited | Wholesale & retail | 2019 |
| TIM Downing Limited | Wholesale & retail | 2003 |
| Timan Construction Ltd | Construction | 2021 |
| Time Security Training Ltd | Education | 2014 |
| Timing Consulting Ltd | Professional & scientific | 2020 |
| Timur's Ltd | Wholesale & retail | 2020 |
| Tints Direct Limited | Other services | 1999 |
| Tiny Shark Accounting Ltd | Professional & scientific | 2025 |
| Tirley Consulting Limited | Information & communication | 2019 |
| Titan Facilities London Limited | Administrative & support | 2021 |
| Tithe Court Management Association Limited | Households | 1981 |
| Titlewave Ltd | Wholesale & retail | 2014 |
| TM (Abingdon) Management Company Limited | Households | 2004 |
| TM Healthcare Limited | Health & social care | 2018 |
| TM Heating & Plumbing Ltd | Construction | 2016 |
| Tmagination Productions Ltd | Administrative & support | 2019 |
| TMG Marchesini UK Limited | Manufacturing | 1986 |
| Tmguard Ltd | Information & communication | 2026 |
| TN2 Limited | Construction | 2004 |
| Tnhg Limited | Professional & scientific | 2011 |
| TNK Trading Limited | Wholesale & retail | 2015 |
| Tofana Holdings Ltd | Financial services | 2024 |
| Toi’S Thai Kitchen Limited | Hospitality | 2022 |
| Tommy Henry Ltd | Professional & scientific | 2021 |
| Toncol Ltd | Extraterritorial | 2012 |
| Tonic Partners Limited | Other services | 1999 |
| Tony's Fitters Limited | Construction | 2019 |
| Tooicee Ltd | Health & social care | 2022 |
| Toolmonkey Limited | Manufacturing | 1994 |
| Toothpaste Media Ltd | Manufacturing | 2017 |
| Top Dog Promotions Ltd. | Administrative & support | 2001 |
| Top Shelving Ltd | Wholesale & retail | 2013 |
| Top TEE Golf Ltd | Arts & recreation | 2024 |
| Top UPS (UK) Limited | Administrative & support | 2004 |
| Top UPS Services Limited | Other services | 2009 |
| Top-Notch Sheetmetal and Fabrication Limited | Manufacturing | 2026 |
| Topspec Tiling & Bathrooms Limited | Construction | 2015 |
| Topvine Aloud Limited | Real estate | 2004 |
| Topvine Limited | Real estate | 1998 |
| Torquis Limited | Manufacturing | 2002 |
| TOT BOP Franchise Ltd | Arts & recreation | 2026 |
| TOT BOP Ltd | Arts & recreation | 2016 |
| Total Aspects Roofing & Guttering Ltd | Construction | 2024 |
| Total Football Leagues Ltd | Arts & recreation | 2021 |
| Total Valeting Limited | Administrative & support | 2018 |
| Totally IAM Ltd | Information & communication | 2022 |
| Tour DE FUN Rides Ltd | Extraterritorial | 2025 |
| Tourmaline IT Services Limited | Information & communication | 2011 |
| Town & Countryside Land Management Limited | Professional & scientific | 2026 |
| Town and Country Vending Services Limited | Professional & scientific | 1988 |
| TP Security Solutions Limited | Manufacturing | 2014 |
| TQH Tebworth Ltd | Hospitality | 2019 |
| Trade Office Solutions Ltd | Information & communication | 2025 |
| Traditional Project Management LLP | | 2016 |
| Trafalgar House Capital Limited | Professional & scientific | 2019 |
| Traffic Self Drive (Herts) Limited | Administrative & support | 2004 |
| Trailer AID Limited | Wholesale & retail | 2011 |
| Trainar Holdings Ltd. | Information & communication | 2025 |
| Trainar Limited | Information & communication | 2024 |
| Tramontane Solutions Limited | Information & communication | 2025 |
| Trans Logistics 4 U Limited | Transport & logistics | 2016 |
| Transatlantic-O Connector Limited | Financial services | 2024 |
| Transit Forward Ltd | Information & communication | 2024 |
| Transom Square Trading Company Ltd | Real estate | 2013 |
| Trantor Investments Limited | Financial services | 2019 |
| Trash Talk CIC | Health & social care | 2025 |
| Travelgreener Limited | Transport & logistics | 2008 |
| Travers Property Holdings Ltd | Real estate | 2023 |
| Treasure MAP Trails Ltd | Wholesale & retail | 2020 |
| Trebor Capital Ltd | Real estate | 2020 |
| Treebor Gardening Services Ltd | Professional & scientific | 2025 |
| Trendline Solutions Limited | Information & communication | 2019 |
| Treverbyn Limited | Information & communication | 2025 |
| Trevi Poole Ltd | Real estate | 2020 |
| Triadtech Limited | Information & communication | 2025 |
| Triangle Contracts Associates Limited | Other services | 2013 |
| Trinity Hall Biogas 2 Limited | Energy | 2023 |
| Trinity Hall Biogas Limited | Energy | 2011 |
| Trinity Hall Business Park Limited | Real estate | 2023 |
| Trinity House Finance Limited | Financial services | 1995 |
| Trinity House Properties Limited | Real estate | 2002 |
| Triple Helix Estates Ltd | Real estate | 2019 |
| Triton Tooling Ltd | Manufacturing | 2014 |
| TRM Supplies Limited | Manufacturing | 2024 |
| Trust Point Limited | Financial services | 2024 |