| Transformatio Ltd | Information & communication | 2020 |
| Transformation Pilates Ltd | Other services | 2021 |
| Transpace Ltd | Construction | 1995 |
| Transport Video Publishing Limited | Information & communication | 2006 |
| Trec Film & Media Ltd | Information & communication | 2021 |
| Treedoor Limited | Wholesale & retail | 2025 |
| Trees R US Herts Ltd | Administrative & support | 2025 |
| Treestump Property Management Limited | Households | 1982 |
| Tregoney Property Limited | Real estate | 2023 |
| Trehy Productions Limited | Information & communication | 2025 |
| Trestle Theatre Company Limited | Education | 1985 |
| Trestonik Retail Ltd | Construction | 2022 |
| TRG Investments Limited | Information & communication | 2013 |
| Trgf Ltd | Hospitality | 2020 |
| Tri-Son Consultancy Limited | Professional & scientific | 2025 |
| Tri-Tek Pro. Ltd | Manufacturing | 2020 |
| Tria Beauty UK Ltd | Wholesale & retail | 2011 |
| Tribulaun Limited | Professional & scientific | 2025 |
| Trident BI Limited | Information & communication | 2023 |
| Tridentinum Limited | Information & communication | 2020 |
| Trimantic Accountants Ltd | Professional & scientific | 2018 |
| Trimount Properties (Brickfields) Limited | Construction | 2017 |
| Trinacria Collections Ltd | Administrative & support | 2022 |
| Trinity London Care Ltd | Other services | 2005 |
| Tripbuddy UK Limited | Administrative & support | 2017 |
| Triplepinch Limited | Professional & scientific | 2017 |
| Triplo Limited | Administrative & support | 2024 |
| Tristen Knight Garden Design Ltd | Administrative & support | 2016 |
| Trmg Limited | Information & communication | 1996 |
| Troon Construction Limited | Construction | 2022 |
| Trowler Property Services UK Ltd | Real estate | 2023 |
| TRU Forme Ltd | Manufacturing | 2024 |
| Truesignal Ltd | Manufacturing | 2014 |
| Trurating Limited | Information & communication | 2012 |
| Trust Hire Solutions Ltd | Administrative & support | 2022 |
| Trusted Hands Herts Ltd | Health & social care | 2019 |
| TS & a Solutions Ltd | Administrative & support | 2022 |
| TS HR Ltd | Professional & scientific | 2014 |
| TSC STA Limited | Other services | 2019 |
| TSE Marketing Group Ltd | Professional & scientific | 2025 |
| TSI Propco Ltd | Real estate | 2020 |
| TSN Automotive Limited | Administrative & support | 2001 |
| Tuckers Holdings 171 Ltd | Real estate | 2025 |
| Tudo's Family Limited | Wholesale & retail | 2022 |
| Tudor Smith Investments Limited | Real estate | 1999 |
| Tudor Wine Limited | Wholesale & retail | 2015 |
| Tuen Limited | Real estate | 2016 |
| Tuesday's Child Kids Ltd | Wholesale & retail | 2023 |
| Tufton VC II LP | | 2025 |
| Tulip London Ltd. | Administrative & support | 2013 |
| Tulip Property Services Ltd | Construction | 2014 |
| Tuntum-Swan Assets Ltd | Professional & scientific | 2026 |
| Turk & Co Limited | Professional & scientific | 2010 |
| Turners Hall Barns Limited | Households | 2018 |
| Turstin Court Management Company Limited | Households | 2019 |
| Turtles House Limited | Professional & scientific | 2016 |
| Turus Limited | Professional & scientific | 2009 |
| TW Audio Distribution UK Ltd | Wholesale & retail | 2017 |
| TW Audio UK Limited | Wholesale & retail | 2011 |
| TW Goalkeeping Limited | Arts & recreation | 2024 |
| Twelve Specialist Risk Limited | Financial services | 2015 |
| Twenty One From Eight Ltd | Manufacturing | 2021 |
| Twiggs (2012) Ltd | Construction | 2012 |
| Twin Steel Limited | Real estate | 2015 |
| Two Hats Management Ltd | Arts & recreation | 2025 |
| Two Together Designs Ltd | Wholesale & retail | 2019 |
| Two Trinity Ltd | Professional & scientific | 2020 |
| TWO43 Ltd | Information & communication | 2019 |
| Tyagi Healthcare Ltd | Health & social care | 2021 |
| Typical Girl Ltd | Arts & recreation | 2025 |
| Tyre Trax (UK) Ltd | Wholesale & retail | 2009 |
| Tyrian Capital Limited | Financial services | 2013 |
| TYT Logistics Limited | Transport & logistics | 2017 |
| TYT Solutions Ltd | Information & communication | 2014 |
| Tzavali Consulting Ltd | Professional & scientific | 2019 |
| UA Construction Services Ltd | Construction | 2022 |
| Uafya Community Interest Company | Professional & scientific | 2023 |
| UAL Bar & Restaurants Ltd | Hospitality | 2024 |
| Ubex Service Ltd | Wholesale & retail | 2024 |
| Ubidock (UK) Limited | Administrative & support | 2014 |
| UC Distribution Ltd | Hospitality | 2020 |
| Ucpc Ltd | Administrative & support | 2026 |
| UF I Nominees Limited | Financial services | 2023 |
| Ugpartners Ltd | Professional & scientific | 2026 |
| Uhuru Limited | Information & communication | 2024 |
| UI Centric Holdings Limited | Financial services | 2016 |
| UI Centric Limited | Extraterritorial | 2023 |
| UK Corporate Finance Ltd | Financial services | 2005 |
| UK Damp and Mould Ltd | Construction | 2026 |
| UK Federation of Chinese Schools | Other services | 1996 |
| UK Film Cars Limited | Transport & logistics | 2015 |
| UK Medical Space Limited | Real estate | 2021 |
| UK Metrology Board Ltd | Professional & scientific | 2022 |
| UK Nama Constructions Ltd | Construction | 2023 |
| UK Power Connections Ltd | Construction | 2024 |
| UK Trade Windows Ltd | Construction | 2007 |
| UK Weighing Federation Ltd | Other services | 2000 |
| UK Windows (Surrey) Limited | Construction | 2010 |
| Ukrainian Saturday School of Herts C.I.C. | Education | 2023 |
| Ultimate Dance Productions Ltd | Arts & recreation | 2020 |