| Thomas David Consulting Limited | Professional & scientific | 2025 |
| Thomas English Partnership LLP | | 2010 |
| Three Blue Circles Limited | Information & communication | 2016 |
| Threeways (Teddington) Residents Association Limited | Households | 1967 |
| Thurnby Residents Association Limited | Households | 1958 |
| Tibor Pahi Ltd | Transport & logistics | 2024 |
| Tickle Creative Limited | Professional & scientific | 2012 |
| Tidda Limited | Real estate | 2018 |
| Tide END Consulting Limited | Professional & scientific | 2015 |
| Tide END Health Ltd | Arts & recreation | 2026 |
| Tide END Holdings Limited | Financial services | 2020 |
| Tierra Capital Limited | Real estate | 2021 |
| Tierra Consulting Limited | Professional & scientific | 2022 |
| Tierra CR2 Limited | Construction | 2016 |
| Tierra Developments Limited | Construction | 2013 |
| Tierra EV Limited | Financial services | 2022 |
| Tijalu Limited | Administrative & support | 2025 |
| TIM Miller Design Ltd | Arts & recreation | 2017 |
| Timec 1664 Limited | Administrative & support | 2018 |
| Tinted Nails Ltd | Other services | 2023 |
| Tioman Consulting Ltd | Information & communication | 2016 |
| Tkjl Services Limited | Financial services | 2014 |
| TL Partners Limited | Administrative & support | 2016 |
| TLB Communication Ltd | Professional & scientific | 2018 |
| TLC BID Works Limited | Professional & scientific | 2021 |
| Toast Trinity Limited | Hospitality | 2023 |
| Toccata Bella Limited | Financial services | 2021 |
| TOM GOY Property Consultants Limited | Other services | 2017 |
| TOM Littlechild Consulting Ltd | Professional & scientific | 2026 |
| Tona the Label Limited | Wholesale & retail | 2020 |
| Toni Calliva Ltd | Administrative & support | 2015 |
| Top Tier Roofing Limited | Construction | 2026 |
| Tophouse Adelaide Limited | Hospitality | 2025 |
| Topocrew Ltd | Professional & scientific | 2009 |
| Touching Lives International Ministries Ltd | Other services | 2021 |
| Townstone (KEW Road) Management Company Limited | Households | 1977 |
| TPG Estates Ltd | Real estate | 2026 |
| TPR Investments Limited | Professional & scientific | 2019 |
| TPS Tax Services Ltd | Professional & scientific | 2018 |
| TQ Hummingbird Holdco Limited | Financial services | 2024 |
| TQ Hummingbird Limited | Information & communication | 2023 |
| TQA Holdco Limited | Financial services | 2020 |
| Tquila Automation Ltd | Information & communication | 2019 |
| Trading College Ltd | Administrative & support | 2009 |
| Trap Homes Limited | Real estate | 2023 |
| Travyond UK Ltd | Administrative & support | 2025 |
| Trela Renovations Ltd | Construction | 2017 |
| Trellis AI Limited | Information & communication | 2026 |
| Trentfd Ltd | Professional & scientific | 2022 |
| TRF Construction Ltd | Construction | 2025 |
| Trickcam Limited | Information & communication | 2014 |
| Triggerpoint Software Ltd. | Information & communication | 2015 |
| Trim Left Ltd | Information & communication | 2019 |
| Trinder Mews (Teddington) Limited | Households | 2002 |
| Trinity Consultants (UK) Limited | Professional & scientific | 2006 |
| TRIPLE2 Investments Limited | Real estate | 2023 |
| Trity Group Ltd. | Wholesale & retail | 2014 |
| Tronway Limited | Real estate | 1992 |
| Tropic Nation Limited | Arts & recreation | 2018 |
| Trotters Independent Trimming Limited | Information & communication | 2017 |
| True North Leaders Ltd | Professional & scientific | 2018 |
| Truly Wise Trading Ltd | Wholesale & retail | 2026 |
| Trusted Honest Workers Limited | Administrative & support | 2022 |
| TST Professional Services Ltd | Professional & scientific | 2018 |
| Turnkey Creations Limited | Real estate | 2011 |
| Turquoise (UK) Limited | Information & communication | 2008 |
| TW11 8BY Grovers Limited | Households | 2025 |
| TW11 Design, Build & Living Ltd | Real estate | 2023 |
| TW11 Investments Limited | Real estate | 2023 |
| Twelvenoon Projects Limited | Information & communication | 2024 |
| Twickenham Airconditioning Ltd | Construction | 2018 |
| Twickenham Developments Limited | Real estate | 2003 |
| Twiggy Comms Limited | Professional & scientific | 2020 |
| Twilight Electrical Services Ltd | Construction | 2020 |
| Two Eight One Limited | Information & communication | 2008 |
| Two Mustard Bytes Ltd | Information & communication | 2023 |
| Twoppeople LLP | | 2023 |
| Type Fiend Ltd. | Professional & scientific | 2017 |
| Tyrant Productions Limited | Arts & recreation | 2000 |
| Udney Park Holdings Ltd | Financial services | 2025 |
| Udney Park Playing Fields Trust | Arts & recreation | 2017 |
| Uilario Limited | Health & social care | 2024 |
| UK Korea Education Hub C.I.C. | Education | 2020 |
| UK Spa Association | Other services | 2013 |
| Uk-China Business Solutions Limited | Real estate | 2004 |
| Ukeh Ltd | Education | 2025 |
| Ukua Trading Limited | Transport & logistics | 2022 |
| Ultramarine Capital Management Limited | Financial services | 2013 |
| Umay Prevention CIC | Education | 2026 |
| Unbnd Blanks Ltd | Wholesale & retail | 2022 |
| Uni-T Healthcare Solutions Ltd | Health & social care | 2015 |
| Unifeye Ltd | Information & communication | 2025 |
| Unified Communications Technology Ltd | Information & communication | 2023 |
| United Response | Other services | 1973 |
| United Response Services Ltd | Administrative & support | 2019 |
| Universal Cleaning Group Ltd | Administrative & support | 2019 |
| Urban Holdings Limited | Real estate | 2021 |
| Urban Red (Hampton) Limited | Real estate | 2020 |
| Urban Red (Richmond) Ltd | Real estate | 2025 |
| Urban Red (UK) Ltd | Real estate | 2011 |