| Train Works Ltd | Extraterritorial | 2004 |
| Trainer Investments Limited | Real estate | 2016 |
| Trallwyn Limited | Real estate | 2015 |
| Trams of Mumbles Ltd | Hospitality | 2016 |
| Trams@Mumbles Limited | Hospitality | 2024 |
| Tran TA WON Ltd | Hospitality | 2008 |
| Trans Media Technology Limited | Administrative & support | 1976 |
| Transform AG Limited | Professional & scientific | 2020 |
| Transform Your Life Ltd | Health & social care | 2018 |
| Transformation 4 Business Limited | Professional & scientific | 2014 |
| Transformation Project Management Services Limited | Professional & scientific | 2017 |
| Transmita Ltd | Transport & logistics | 2019 |
| Transoil Lubricants Limited | Manufacturing | 2020 |
| Transworld Consortium Ltd | Professional & scientific | 2024 |
| Tranz Vanz Limited | Wholesale & retail | 2011 |
| Trawler Road Management Limited | Households | 2019 |
| Trawscoed Limited | Real estate | 1994 |
| TRC Groundworks & Construction Ltd | Construction | 2026 |
| Treadecatering Limited | Hospitality | 2021 |
| Treasured Moments Photography Ltd | Professional & scientific | 2015 |
| Treatnow Limited | Other services | 2013 |
| Trebanos Rugby Limited | Hospitality | 2014 |
| Treboeth Developments Limited | Extraterritorial | 2004 |
| Treboeth Interiors Limited | Construction | 2001 |
| Treboeth Stop & Shop Ltd | Wholesale & retail | 2025 |
| Trebor Hospitality Limited | Hospitality | 2025 |
| Tree Society Community Interest Company | Agriculture & fishing | 2024 |
| Treehouse London Limited | Arts & recreation | 2013 |
| Treforys GAS Solutions Ltd | Construction | 2019 |
| Treforys Tiny Tots Holdings Ltd | Financial services | 2024 |
| Treforys Tiny Tots Limited | Health & social care | 2012 |
| Tregwent (Management) Limited | Households | 2006 |
| Tremolo Studios Limited | Arts & recreation | 2025 |
| Trends Development Ltd | Construction | 2020 |
| Treorchy Carwash Ltd | Health & social care | 2026 |
| Trerise Property Maintenance Ltd | Construction | 2007 |
| Tresham Property Services Limited | Other services | 2019 |
| Tresillian Shaw & Goddard Ltd | Professional & scientific | 2022 |
| Tresreyes Ltd | Hospitality | 2019 |
| Trevelyan Trading Limited | Administrative & support | 2010 |
| Trevor Hinson Ltd | Extraterritorial | 2010 |
| Trewyddfa Road Limited | Real estate | 2017 |
| TRF Motor Group Ltd. | Wholesale & retail | 2026 |
| Trfu Machines 2023 Limited | Manufacturing | 2016 |
| TRH Medical Ltd | Health & social care | 2023 |
| TRI and Enter Events Ltd | Arts & recreation | 2008 |
| Triangl Limited | Construction | 2021 |
| Trible Seven Ltd | Hospitality | 2023 |
| Trick and Treat Limited | Wholesale & retail | 2003 |
| Trick Stuff Limited | Information & communication | 2002 |
| Trickster Films Ltd | Information & communication | 2017 |
| Trident Economics Limited | Professional & scientific | 2020 |
| Trident Jetski Ltd | Manufacturing | 2012 |
| Triggs & James Aesthetics Limited | Other services | 2012 |
| Trilobite Clothing Ltd | Wholesale & retail | 2025 |
| Trimark Music Ltd | Information & communication | 2013 |
| Trimaway Ltd | Other services | 2024 |
| Trimology Gorseinon Limited | Other services | 2024 |
| Trimology Limited | Other services | 2018 |
| Trimology Swansea Ltd | Other services | 2024 |
| Trinity Cosmetic Ltd | Other services | 2021 |
| Trinity Landmark Limited | Real estate | 2023 |
| Trinity Life Limited | Real estate | 2018 |
| Trinity Management Limited | Real estate | 2019 |
| Trinity Metals (Swansea) Limited | Wholesale & retail | 2014 |
| Trinity Protect Limited | Wholesale & retail | 2023 |
| Trinity Saint David Students' Union | Education | 2014 |
| Triple HIT Collective Limited | Wholesale & retail | 2026 |
| Triple M&B Limited | Real estate | 2011 |
| Triple P Projects Ltd | Construction | 2007 |
| Trisha Scrine Cutting IT Limited | Other services | 2006 |
| Triton Cleantech Ltd | Manufacturing | 2016 |
| Tritorc UK Limited | Wholesale & retail | 2023 |
| TRL Project Management Ltd | Professional & scientific | 2025 |
| TRM Academy Ltd | Other services | 2018 |
| TRM Flex Limited | Information & communication | 2026 |
| Troupial Consulting Ltd. | Information & communication | 2014 |
| TRT Property Group SPV Ltd | Real estate | 2024 |
| Trtr Group Ltd | Construction | 2025 |
| Truck and Plant Asset Management Limited | Wholesale & retail | 2014 |
| Truck Plant Agri Limited | Manufacturing | 2026 |
| Trucks UN Limited | Extraterritorial | 2023 |
| Trucore Build Group Ltd | Construction | 2025 |
| True Focus Care Ltd | Administrative & support | 2020 |
| True Form Solutions Ltd | Professional & scientific | 2024 |
| True Hawk Ltd | Wholesale & retail | 2025 |
| True Installations Ltd | Construction | 2022 |
| True Legend Limited | Other services | 2017 |
| True North Enterprises Ltd | Real estate | 2025 |
| True North Quantity Surveying Ltd | Construction | 2022 |
| Truebuild Properties Limited | Real estate | 2021 |
| Truebuild South Wales Ltd | Construction | 2008 |
| Truecoat Limited | Construction | 2024 |
| Truecore Electrics Ltd | Construction | 2025 |
| Truefix Developments Limited | Manufacturing | 2025 |
| Trueflow Surveys Ltd | Professional & scientific | 2003 |
| Truesdale Stores (Yeovil) Limited | Real estate | 1976 |
| Truffle Swansea Limited | Hospitality | 2010 |
| Truhoops Ltd | Wholesale & retail | 2025 |
| Trulyte Limited | Other services | 2015 |