| T D Shah Construction & Management Ltd | Construction | 2012 |
| T Gilmartin Holdings Limited | Financial services | 2016 |
| T Golmantas Ltd | Construction | 2011 |
| T Interiors Ltd | Professional & scientific | 2021 |
| T J Electrical & Communications Limited | Manufacturing | 1999 |
| T J Luke Construction Limited | Construction | 2005 |
| T Liners Salon Ltd | Other services | 2018 |
| T&F Investments Limited | Real estate | 2020 |
| T&H Builders and Construction Ltd | Construction | 2025 |
| T&L Fuel Ltd | Wholesale & retail | 2015 |
| T&L Property Services Ltd. | Real estate | 2016 |
| T&L Store Ltd | Wholesale & retail | 2020 |
| T&S Security Ltd | Financial services | 2020 |
| T&T Contractors Watford Ltd | Construction | 2023 |
| T. Brown & Sons (Wireworkers) Limited | Manufacturing | 1963 |
| T.F. Tull Limited | Construction | 1971 |
| T.I.M.E. Construct Limited | Construction | 2021 |
| T.J.Harman & Sons Limited | Agriculture & fishing | 1951 |
| T.M.A. Investments Limited | Real estate | 2024 |
| T.O. Cdcs Ltd | Other services | 2023 |
| T.S.C. Trading Co. Limited | Real estate | 1998 |
| T12 Real Estate Limited | Real estate | 2023 |
| T2E Consulting Ltd | Professional & scientific | 2024 |
| T5HUB Ltd | Hospitality | 2026 |
| TA Financing Ltd | Financial services | 2024 |
| Taana Baana Ltd | Wholesale & retail | 2025 |
| Tabard RFC Supporters Club Limited | Arts & recreation | 2012 |
| Table Hall Nursery Limited | Education | 2008 |
| Tablet Holdings Limited | Health & social care | 2016 |
| Tacbo (UK) Limited | Wholesale & retail | 2014 |
| Tadpoles Limited | Real estate | 2009 |
| Taft Solutions Ltd | Professional & scientific | 2023 |
| TAG Builders Ltd | Construction | 2022 |
| TAG Company (UK) Limited | Administrative & support | 2003 |
| Taghill Limited | Real estate | 1995 |
| Taiho Pharma Europe, Limited | Professional & scientific | 2009 |
| Tailor Made Music Limited | Information & communication | 1996 |
| Tailormade Scaffolding Ltd | Construction | 2025 |
| Taiuk PTY Ltd | Professional & scientific | 2015 |
| TAJ Easy Rent Services Ltd | Real estate | 2024 |
| TAK Trading Limited | Hospitality | 2021 |
| Take and Go Watford Ltd | Hospitality | 2026 |
| TAKE2LIFE Ltd | Health & social care | 2013 |
| Takeverse Limited | Real estate | 1991 |
| Talea Care 1 Ltd | Financial services | 2025 |
| Talea Care 2 Limited | Financial services | 2026 |
| Talea Care Group 2 Ltd | Financial services | 2026 |
| Talea Care Group Ltd | Financial services | 2025 |
| Talea ZZ 2 Limited | Financial services | 2026 |
| Talent Group Partners Limited | Professional & scientific | 2017 |
| Talent Makers Ltd | Professional & scientific | 2025 |
| Talent Octopus Limited | Administrative & support | 2015 |
| Talent Rocket Solutions Limited | Administrative & support | 2025 |
| Talentedge Limited | Real estate | 1986 |
| Talento Real Estate Ltd | Real estate | 2021 |
| Talentstack Recruitment Ltd | Administrative & support | 2020 |
| Tality Social Ltd | Professional & scientific | 2023 |
| Talkfree Design Limited | Real estate | 1996 |
| Talkfree Design NE Ltd | Real estate | 2024 |
| Tallet Solutions Limited | Information & communication | 2009 |
| Tallu Inc. Ltd | Education | 2025 |
| TAM4 Ltd | Information & communication | 2026 |
| Tamai Ltd | Wholesale & retail | 2026 |
| Tamber Property Services Limited | Real estate | 2012 |
| Tamron UK Limited | Professional & scientific | 2002 |
| Tams Commercial Cleaning Limited | Administrative & support | 2022 |
| TAN Physio Ltd | Health & social care | 2025 |
| Tanaplan Limited | Extraterritorial | 1986 |
| Taner KAY Limited | Information & communication | 2016 |
| Tangerine Dream Consulting Ltd | Professional & scientific | 2016 |
| Tanit House Ltd | Information & communication | 2023 |
| Tankabury Online Limited | Information & communication | 2022 |
| Tanrose Group Ltd | Wholesale & retail | 2025 |
| Tanysh Holding LLP | | 2024 |
| Tanysh Ltd | Real estate | 2017 |
| TAO Infinity Limited | Real estate | 2020 |
| TAP and Rate Ltd | Professional & scientific | 2023 |
| TAP Couriers Ltd | Transport & logistics | 2026 |
| Taplx Ltd | Information & communication | 2026 |
| Taptix Ltd | Information & communication | 2012 |
| Taraben Investments Ltd | Real estate | 2013 |
| Tarboush Ltd | Hospitality | 2018 |
| Tarboush Tring Ltd | Hospitality | 2024 |
| Tarcom Enterprises Limited | Other services | 2000 |
| Target Big Data Ltd | Information & communication | 2022 |
| Target Project Consulting Ltd | Professional & scientific | 2015 |
| Target Student Media Limited | Education | 2013 |
| Tarn International Ltd | Administrative & support | 2020 |
| Tarrant Place Management Company Limited | Households | 1989 |
| Tartary Management Limited | Households | 1989 |
| Tasaray Wellness Limited | Health & social care | 2025 |
| Task Contracting Ltd | Information & communication | 2012 |
| Task Netix Ltd | Information & communication | 2025 |
| Task Titans Ltd | Administrative & support | 2025 |
| Tasmay Logistics Ltd | Wholesale & retail | 2025 |
| Tasmim Group Ltd | Wholesale & retail | 2026 |
| Tasmim Ltd | Wholesale & retail | 2026 |
| Taste Makers Kitchen Limited | Manufacturing | 2025 |
| Taste of Lahore (Watford) Limited | Hospitality | 2012 |
| Taste of Sicily Limited | Wholesale & retail | 1999 |