| Thomas Estates Management Limited | Construction | 2022 |
| Thornton Performance Consulting Limited | Financial services | 2018 |
| Thoroughbred Surfacing Consulting Ltd | Construction | 2026 |
| Thrive PR and Events Limited | Other services | 2025 |
| Thunder Court Maisonettes Limited | Households | 2010 |
| Thundercourt (Residents Association) Limited | Households | 1975 |
| Thurston Smith International Limited | Administrative & support | 2017 |
| Tidal IT Limited | Wholesale & retail | 2023 |
| Tiger Lillys Florists Limited | Wholesale & retail | 2014 |
| Tiger Twenty Limited | Administrative & support | 2017 |
| Tigers Consulting Services Ltd | Professional & scientific | 2024 |
| Tilecraft Flooring Ltd | Construction | 2015 |
| Tiled Roof Conservatories (Dorset) Ltd | Construction | 2023 |
| Tilesy Limited | Real estate | 2019 |
| Tillman UK Trading Ltd | Financial services | 2026 |
| Tilney Trading Limited | Financial services | 2024 |
| TIM Burr Ltd | Agriculture & fishing | 2017 |
| TIM the Gardener Limited | Extraterritorial | 2021 |
| Timart Investments Ltd | Real estate | 2023 |
| Timber Tech Limited | Construction | 2003 |
| Timeless Interiors Ltd | Construction | 2019 |
| Tinc Holdings Ltd | Manufacturing | 2024 |
| Tinhouse Industry Limited | Manufacturing | 2003 |
| Tiny Toes (Hertford) Ltd | Education | 2017 |
| Tiny Toes Capital Limited | Health & social care | 2023 |
| Tiny Trendz Ltd | Wholesale & retail | 2023 |
| Titan Group Ltd | Construction | 2019 |
| Titan Properties Services Limited | Real estate | 2024 |
| Titchens Limited | Administrative & support | 2007 |
| Titon Claim Ltd | Financial services | 2025 |
| TJ Tolson Services Ltd | Construction | 2023 |
| TJB Site Engineers Ltd | Construction | 2015 |
| TKC Housing Limited | Construction | 2021 |
| TKK Software Solutions Ltd | Information & communication | 2017 |
| TMB Tax Consultancy Limited | Professional & scientific | 2018 |
| Toast Management Limited | Arts & recreation | 2024 |
| Toby Sowery Racing Limited | Arts & recreation | 2013 |
| Toby’S Glass Ltd | Wholesale & retail | 2025 |
| Today & Tomorrows People Solutions Ltd | Extraterritorial | 2021 |
| Todd Sutherland Photo Ltd | Professional & scientific | 2013 |
| Tolby Limited | Wholesale & retail | 2020 |
| Tolmers Park Residents Association Limited | Other services | 1986 |
| TOM Ashley Limited | Other services | 2015 |
| TOM Walkinshaw Racing Limited | Administrative & support | 2007 |
| Tomyflo Limited | Real estate | 2023 |
| Tony's Pita Group Ltd | Financial services | 2023 |
| Top Gyros Ltd | Hospitality | 2023 |
| Topjet Limited | Wholesale & retail | 1986 |
| Topsec Limited | Construction | 2025 |
| Tornado Kart Engines Limited | Professional & scientific | 2018 |
| Toro Fire and Security Limited | Construction | 2026 |
| Total Combat Limited | Arts & recreation | 2014 |
| Total Property Solutions London Ltd | Construction | 2024 |
| Total Vehicle Sales Ltd | Wholesale & retail | 2013 |
| Touchline Football Limited | Information & communication | 2023 |
| Tour Box Limited | Administrative & support | 2009 |
| TPP Mechanical and Fire Protection Limited | Wholesale & retail | 2022 |
| TR Bland Limited | Administrative & support | 2012 |
| Tracey Jane Fashion Limited | Wholesale & retail | 2018 |
| Trade Office Enfield Limited | Administrative & support | 2011 |
| Trading Law Consultancy Ltd | Professional & scientific | 2006 |
| Trading UP Limited | Administrative & support | 2020 |
| Trailgrazers (Hertfordshire) Limited | Agriculture & fishing | 2026 |
| Trailgrazers Farm School Limited | Education | 2026 |
| Train That Brain Ltd | Education | 2020 |
| Transparatech Ltd | Professional & scientific | 2016 |
| Treeo.Studio Ltd | Professional & scientific | 2025 |
| Trellis Coaching and Consulting Ltd | Professional & scientific | 2018 |
| Trendway App Ltd | Information & communication | 2020 |
| Tresana Property Limited | Construction | 2021 |
| Trevelyan Place Management Company Limited | Households | 2002 |
| Trevillion Holdings Limited | Administrative & support | 2004 |
| Trevor Lukey Thompson Ltd | Extraterritorial | 2024 |
| Triborough Opportunities | Education | 2012 |
| Trinity Court Management Company Limited | Households | 1971 |
| Trinity Court N21 Limited | Households | 2000 |
| Triple FUN Care Ltd | Health & social care | 2025 |
| Triplevel Limited | Administrative & support | 1990 |
| Trust and Succession Planners Ltd | Professional & scientific | 2019 |
| Truth in Focus UFO Prints LLP | | 2026 |
| Tryfan Properties Limited | Construction | 2017 |
| TS Transportations Ltd | Transport & logistics | 2018 |
| TSR EOT Limited | Extraterritorial | 2024 |
| Tt&T Services London Ltd | Construction | 2019 |
| Tuch Consulting Limited | Professional & scientific | 2009 |
| Tulsesense Limited | Real estate | 1985 |
| TUM Consultancy Limited | Information & communication | 2026 |
| Tumbling Bay Fishing Ltd | Agriculture & fishing | 2022 |
| Tungsten Capital UK Limited | Administrative & support | 2019 |
| Tuppence Exports Limited | Administrative & support | 2024 |
| Turkish Kitchen Hertford Ltd | Hospitality | 2016 |
| Tv-Sas Herts & Essex Ltd | Extraterritorial | 2007 |
| TVM Painting Finishes Limited | Construction | 2017 |
| TW Jones & Sons Ltd | Construction | 2015 |
| TWC Events Limited | Education | 2022 |
| TWG Concierge Limited | Wholesale & retail | 2023 |
| Twink Candle Company Limited | Wholesale & retail | 2023 |
| Twisted Solutions Limited | Information & communication | 2014 |
| Two First Names Ltd | Professional & scientific | 2016 |
| Two Left Sheep Limited | Wholesale & retail | 2017 |