| THP Media Ltd | Information & communication | 2024 |
| Three Internet Limited | Information & communication | 2003 |
| Three Oaks Building Limited | Construction | 2018 |
| Three Oaks Care Home Limited | Health & social care | 2002 |
| Three Shires Farm Limited | Agriculture & fishing | 2015 |
| Three Ventures Limited | Professional & scientific | 2011 |
| Three's a Company Ltd | Construction | 2024 |
| Threlfall Consulting Ltd | Professional & scientific | 2025 |
| Thwellbeing Ltd | Other services | 2025 |
| Tiaco Limited | Administrative & support | 2017 |
| Tiago Business Systems Limited | Information & communication | 2009 |
| Ticket Refund Services Limited | Extraterritorial | 2017 |
| Tietie Tuimauga Ltd | Wholesale & retail | 2026 |
| Tiffin S a Limited | Arts & recreation | 2013 |
| Tiger Medical Supplies Limited | Professional & scientific | 2011 |
| Tight Side Latex Limited | Wholesale & retail | 2020 |
| Tika-Tore Ltd. | Administrative & support | 2002 |
| Tikka Nation Inc Limited | Hospitality | 2022 |
| Tile & Mosaic ST Albans Ltd | Construction | 2021 |
| Tilsworth Developments Limited | Construction | 2004 |
| TIM DIM Limited | Wholesale & retail | 2025 |
| TIM K Construction Limited | Construction | 2008 |
| Time Bakery Limited | Manufacturing | 2024 |
| Time to Give Network CIC | Information & communication | 2023 |
| TIME2BMR Ltd | Construction | 2025 |
| Timeframed Ltd. | Manufacturing | 2015 |
| Timesbridge Ltd | Real estate | 2018 |
| Timeworks Ltd | Professional & scientific | 2025 |
| Timsmith Heat Exchangers Ltd | Professional & scientific | 2019 |
| Tina Cockhill Hand Therapist Limited | Health & social care | 2017 |
| Tindall Security Limited | Administrative & support | 1998 |
| Tinkletorium Limited | Wholesale & retail | 2021 |
| Tiny Coconuts Ltd | Wholesale & retail | 2024 |
| Tiny Tastemakers Ltd | Education | 2023 |
| Tioopo Continuation LLP | | 2023 |
| Tipsy Turtle Strategy and Design Limited | Professional & scientific | 2017 |
| Tiptopforlife Music Group Limited | Information & communication | 2013 |
| Tiptopforlife Radiance Limited | Administrative & support | 2018 |
| Tirimaga Limited | Information & communication | 2023 |
| Titan Estates & Construction Ltd | Construction | 2025 |
| Titan First Ltd | Construction | 2026 |
| Tithe Barn Consulting Ltd | Health & social care | 2012 |
| Titi Oluwadare and Associates Ltd. | Wholesale & retail | 2020 |
| TJ Culture Ltd | Professional & scientific | 2023 |
| TJL Luton Ltd | Real estate | 2026 |
| TJL Marketing Limited | Extraterritorial | 2002 |
| TK Security & Training Services Ltd | Administrative & support | 2011 |
| TLC Event Solutions Ltd | Professional & scientific | 2014 |
| TLO Coffee Roastery Limited | Manufacturing | 2020 |
| TML Sports Connections Ltd | Other services | 2014 |
| TMW Electrical Limited | Construction | 2015 |
| TMZ Web Development Ltd | Information & communication | 2011 |
| TND Drilling Limited | Construction | 2007 |
| TNK Lettings Limited | Real estate | 2021 |
| TNK Properties Holding Limited | Financial services | 2021 |
| TNK Transport Limited | Transport & logistics | 2016 |
| Toddington Eyecare Ltd | Wholesale & retail | 2023 |
| Tofts Capital Ltd | Financial services | 2023 |
| Tofu Craft Ltd | Manufacturing | 2025 |
| Tollgate Associates Ltd | Professional & scientific | 2019 |
| Tollgate Farm Property Ltd | Real estate | 2021 |
| TOM Fallon Photography Ltd | Professional & scientific | 2017 |
| Tomlitech Ltd | Professional & scientific | 2024 |
| Tommy WU Limited | Professional & scientific | 2021 |
| Tomorrow's Energy Ltd | Construction | 2006 |
| Toms Wood Homes Limited | Construction | 2017 |
| Tonal Drivers Space Ltd | Professional & scientific | 2021 |
| Tonkin Developments Ltd | Real estate | 2013 |
| Tony French Limited | Information & communication | 2016 |
| Tony Gates Consultancy (UK) Limited | Professional & scientific | 2025 |
| Tony Jackson Executive Coaching Limited | Professional & scientific | 2024 |
| Tony Jackson Limited | Professional & scientific | 2024 |
| Tony Mcdermott Art Ltd | Wholesale & retail | 2022 |
| Top Tier Financial Services Ltd | Professional & scientific | 2009 |
| Topmak Consulting Limited | Information & communication | 2006 |
| Tops Pizza ST Albans Ltd | Hospitality | 2025 |
| Torchwood Coaching Ltd | Administrative & support | 2023 |
| Total Care Personal Training Ltd | Education | 2014 |
| Total Design Structural Ltd | Professional & scientific | 2013 |
| Total Group International Limited | Manufacturing | 2000 |
| Totalcow Limited | Hospitality | 2021 |
| Totali Communications Ltd | Information & communication | 2024 |
| Touch of Spice Ltd | Hospitality | 2023 |
| Touchspot Audio Limited | Information & communication | 2021 |
| Tower Lodge Properties Limited | Construction | 2016 |
| Town & Country Edlesborough Limited | Real estate | 2016 |
| Town & Country Markyate Ltd | Real estate | 2002 |
| Town TUB (the Denes) Limited | Other services | 1978 |
| Townstone Limited | Real estate | 2004 |
| Tpmc Limited | Construction | 2011 |
| Trackvision AI Ltd | Information & communication | 2023 |
| Trade Electrical Supplies Limited | Administrative & support | 2014 |
| Trade Star (London) Limited | Wholesale & retail | 2010 |
| Tradesman Link Limited | Information & communication | 2011 |
| Training Tails Limited | Other services | 2017 |
| Transcendental Ltd | Health & social care | 2022 |
| Transcensus Ltd | Information & communication | 2026 |
| Transferfine Limited | Real estate | 1978 |
| Transform Contracting Limited | Construction | 2010 |
| Transform-It Consulting Limited | Information & communication | 2012 |