| Thinkbeforeyouink Limited | Other services | 2016 |
| Thinkweaver Digital Ltd | Information & communication | 2019 |
| Third AGE Moves Limited | Transport & logistics | 2026 |
| Third Edge Ltd | Professional & scientific | 2003 |
| Third EYE Brew Co. Ltd | Manufacturing | 2022 |
| Third EYE Therapies Limited | Other services | 2026 |
| Third EYE Traveller Ltd | Information & communication | 2021 |
| Thirst Design Ltd | Information & communication | 2019 |
| THIRST4 Consulting Ltd | Professional & scientific | 2019 |
| Thirteen-Ten Nanometre Networks Limited | Information & communication | 2018 |
| Thistle Cleaning Company Ltd | Administrative & support | 2024 |
| Thistle Rose Properties Ltd | Real estate | 2021 |
| Thomas Commercial Cleaning Limited | Administrative & support | 2003 |
| Thomas Davies Ltd | Real estate | 2023 |
| Thomas Hitchcock Associates Limited | Professional & scientific | 2003 |
| Thompson Plumbing Services Limited | Construction | 2016 |
| Thompson Telecoms Solutions Ltd | Manufacturing | 2016 |
| Thompsons GRP Limited | Construction | 2022 |
| Thomzo Ltd | Professional & scientific | 2009 |
| Thor Utility’S Limited | Other services | 2025 |
| Thornton Associates Surveyors Limited | Professional & scientific | 2006 |
| Thornton Independent Ltd | Construction | 2024 |
| Thought and Mortar Limited | Information & communication | 2016 |
| Thread Grinding Services Limited | Manufacturing | 1984 |
| THREAD79 Ltd | Wholesale & retail | 2025 |
| Threads and Canvas Limited | Wholesale & retail | 2025 |
| Three Bears Cookery Club Franchise Ltd | Professional & scientific | 2021 |
| Three Peaks Investments Limited | Real estate | 2023 |
| Three Stars Trading Ltd | Wholesale & retail | 2019 |
| Three Strikes Limited | Professional & scientific | 2025 |
| Three Trees Farm LLP | | 2010 |
| Threeeyes Ltd | Administrative & support | 2018 |
| Thrings (Services) Limited | Extraterritorial | 2009 |
| Thrings Corporate Services Limited | Professional & scientific | 2019 |
| Thrings LLP | | 2009 |
| Thrion UK Limited | Wholesale & retail | 2017 |
| Thrive Support Services Ltd | Health & social care | 2024 |
| Thrive Trek Ltd | Transport & logistics | 2024 |
| Thrive Tuition & Family Therapy Ltd | Education | 2025 |
| Thryve Health Care Limited | Professional & scientific | 2007 |
| Tibotalent Ltd | Professional & scientific | 2023 |
| Tica Ltd | Information & communication | 2012 |
| Tickled Hippy Ltd | Extraterritorial | 2007 |
| Tidy Build Swindon Limited | Administrative & support | 2025 |
| Tidy by Tesh Cleaning Services Ltd | Administrative & support | 2025 |
| Tidy HEN Limited | Extraterritorial | 2021 |
| Tier One Photos Ltd | Professional & scientific | 2023 |
| Tifelayo Business Limited | Wholesale & retail | 2026 |
| Tiffany Rose Stays Ltd | Hospitality | 2025 |
| Tiger Family Martial Arts LLP | | 2022 |
| Tiger Ladies Kickboxing Ltd | Education | 2022 |
| Tiger Martial Arts Bicester LLP | | 2023 |
| Tiger Martial Arts Oxford Ltd | Education | 2020 |
| Tigersharks ASC Ltd | Arts & recreation | 2015 |
| Tight Software Limited | Administrative & support | 2017 |
| Tika-Torre Limited | Health & social care | 2015 |
| Tikananda & Sons Company UK Limited | Other services | 2011 |
| Tikbooks Ltd | Wholesale & retail | 2026 |
| Tilden Court Residents Association Limited | Households | 1986 |
| Tilden House Freehold Limited | Real estate | 2022 |
| Tile Eco Homes Limited | Construction | 2020 |
| Tile Energy Limited | Energy | 2012 |
| Tilecraft Solution Ltd | Construction | 2022 |
| Tillybud Holdings Ltd | Financial services | 2026 |
| Tilokmaya UK Limited | Hospitality | 2023 |
| Tim-Transport Limited | Transport & logistics | 2014 |
| Timber Windows.Com Limited | Manufacturing | 2007 |
| Timberline Carpentry & Joinery Ltd | Construction | 2021 |
| Time to GET Online Limited | Information & communication | 2004 |
| Timeless Lines Aesthetics Ltd | Other services | 2018 |
| Timetogo Analysis Ltd | Information & communication | 2024 |
| Timothy Bryder Consultancy Ltd | Professional & scientific | 2026 |
| TIN TIN Takeaway (Swindon) Ltd | Hospitality | 2020 |
| Tinuangco Ltd | Construction | 2026 |
| Tiny BUT Mighty Swindon CIC | Wholesale & retail | 2022 |
| Tinymobile Ltd | Administrative & support | 2009 |
| Tinyrocket Ltd | Information & communication | 2016 |
| Tinys Brunch Ltd | Hospitality | 2026 |
| TIP Top Cars Ltd | Other services | 2015 |
| TIP Top Dog Grooming Limited | Other services | 2015 |
| Tipping Point Change Consulting Ltd | Professional & scientific | 2010 |
| TIPS4CHOICES CIC | Education | 2010 |
| Tires for YOU Limited | Wholesale & retail | 2026 |
| Tish and TEE Ltd | Health & social care | 2017 |
| Titan Carpentry Contractors Ltd | Construction | 2018 |
| Titan Funding Limited | Financial services | 2014 |
| Titan Heating & Plumbing Solutions Ltd | Construction | 2020 |
| Tithebarn Apartment Management Limited | Households | 1990 |
| Tithegrove Holdings Limited | Construction | 2015 |
| Tithegrove Limited | Construction | 1984 |
| Titilayo Ventures Limited | Health & social care | 2025 |
| TJ Leisure Swindon Limited | Hospitality | 2014 |
| TJ Wellbeing Ltd | Health & social care | 2021 |
| Tj&Ms | Real estate | 2020 |
| Tj's Aviation Limited | Manufacturing | 1997 |
| Tj's Cafe Ltd | Hospitality | 2021 |
| TJB Automotive Limited | Wholesale & retail | 2025 |
| Tjbpn Holdings Ltd | Financial services | 2024 |
| Tjcmorgan Associates Limited | Information & communication | 2015 |
| TJE Solar Ltd | Construction | 2025 |