| Tapejoint UK Ltd | Construction | 2019 |
| Taplan Limited | Real estate | 2012 |
| Tarran & Co. Financial Planning Ltd | Financial services | 2014 |
| Task Property Management Limited | Households | 2019 |
| Taste Buds (Darlington) Ltd | Hospitality | 2026 |
| Taste Indian Limited | Hospitality | 2017 |
| Tasties D Ltd | Hospitality | 2025 |
| Tasties N Ltd | Hospitality | 2021 |
| Taylor Estates Property Services Limited | Real estate | 2017 |
| Taylor Green Interiors Ltd | Wholesale & retail | 2022 |
| Taymer Boilers and Bathrooms Ltd | Construction | 2024 |
| Taymer Plumbing and Heating Ltd | Construction | 2021 |
| Tazza Foods Ltd | Wholesale & retail | 2019 |
| Tbcc Ltd | Transport & logistics | 2013 |
| TD Prints Ltd | Manufacturing | 2025 |
| TD Trans Ltd | Transport & logistics | 2024 |
| TDW Flooring (UK) Ltd | Construction | 2025 |
| TDW Wood (UK) Ltd | Construction | 2025 |
| Team Finance Limited | Extraterritorial | 1986 |
| Tech Repair NE Ltd | Other services | 2022 |
| Techbridge Distribution Ltd | Wholesale & retail | 2026 |
| Techmech Support Services Limited | Professional & scientific | 2003 |
| Technical Housing Solutions Limited | Professional & scientific | 2008 |
| Technocopy Limited | Extraterritorial | 2021 |
| Technology Doctors Limited | Information & communication | 2011 |
| Techpeak LAB Ltd | Information & communication | 2024 |
| Tecserv (NE) Limited | Professional & scientific | 2013 |
| Teddy's Playground Ltd | Wholesale & retail | 2023 |
| TEE M BEE Ltd | Wholesale & retail | 2021 |
| Teecra Limited | Construction | 2024 |
| Tees Cottage Pumping Station (Darlington) | Arts & recreation | 1989 |
| Tees Grange Engineering Limited | Professional & scientific | 2010 |
| Tees Rivers Charitable Trust | Professional & scientific | 2009 |
| Tees Valley Cabs Limited | Transport & logistics | 2005 |
| Tees Valley Campers & Customs Ltd | Wholesale & retail | 2023 |
| Tees Valley Decor Limited | Construction | 2024 |
| Tees Valley Financial Services Limited | Financial services | 2006 |
| Tees Valley Fire Protection Limited | Public administration | 1995 |
| Tees Valley Lithium Limited | Manufacturing | 2022 |
| Tees Valley Pet Services Limited | Other services | 2023 |
| Tees Valley Plastics Limited | Manufacturing | 2016 |
| Tees Valley Property Group Ltd | Real estate | 2025 |
| Tees Valley Windscreens & Van Locks Ltd | Wholesale & retail | 2022 |
| Tees Valley Young Men's Christian Association | Administrative & support | 1993 |
| Teesdale Memorials (Barnard Castle) Ltd | Other services | 2016 |
| Teesdale Passenger Transport Ltd | Transport & logistics | 2023 |
| Teesdale West Durham Community Interest Company | Administrative & support | 2009 |
| Teesside Airport Foundation | Other services | 2021 |
| Teesside Autotech Limited | Wholesale & retail | 2011 |
| Teesside DIG Ltd | Education | 2023 |
| Teesside Health Co. Ltd | Health & social care | 2018 |
| Teesside International Airport Business Park Limited | Real estate | 2020 |
| Teesside International Airport Limited | Transport & logistics | 1986 |
| Teesside Logistics (NE) Ltd | Transport & logistics | 2019 |
| Teesside Logistics Company Ltd | Transport & logistics | 2025 |
| Teesside Paints Limited | Wholesale & retail | 2014 |
| Teesvale Limited | Financial services | 2003 |
| Teesvalley Transport 2005 Ltd | Transport & logistics | 2017 |
| Teesworks Estate Management Company Limited | Administrative & support | 2025 |
| Tehs Limited | Wholesale & retail | 2020 |
| Tekcloud Ltd | Information & communication | 2020 |
| Teleaerials Ltd | Information & communication | 2012 |
| TEM Property Management Ltd | Real estate | 2025 |
| Tempest Jones Consulting Limited | Administrative & support | 2012 |
| Temple Court Management (Middleton ST. George) (2014) Ltd | Extraterritorial | 2014 |
| Tempus Group Villages Ltd | Health & social care | 2023 |
| Tempus Living Care Ltd | Health & social care | 2025 |
| Tempus Living Projects Ltd | Education | 2025 |
| TEN Image Publishing Limited | Information & communication | 2025 |
| Tender Holdings Limited | Financial services | 2018 |
| Tentacle Promotions Ltd | Wholesale & retail | 2022 |
| TES Taylor Electrical Solutions Ltd | Construction | 2021 |
| Tetford Country Cottages (Management) Ltd | Households | 2024 |
| Teward Recycling Limited | Water & waste | 2013 |
| Tewv Estates and Facilities Management Limited | Administrative & support | 2017 |
| TFH Road Contractors Ltd | Construction | 2018 |
| TG Plastering & Rendering Ltd | Construction | 2025 |
| TGI Media Limited | Professional & scientific | 2015 |
| TGM Specialist Cars Limited | Wholesale & retail | 2021 |
| Thai ME UP Street Food Limited | Hospitality | 2023 |
| Thames Valley Fabrications Limited | Manufacturing | 2005 |
| Thap Ltd | Professional & scientific | 2024 |
| THE A1 Steam Locomotive Trust | Manufacturing | 1991 |
| THE A1SLT Support Services Company Limited | Manufacturing | 2021 |
| THE Accountant NE Ltd | Professional & scientific | 2012 |
| THE Advice Collective Ltd | Financial services | 2026 |
| THE American Dining Car Company Limited | Real estate | 1995 |
| THE Anglers' Lodge Limited | Wholesale & retail | 2014 |
| THE Apps Shed Ltd | Information & communication | 2016 |
| THE Art of Finance Ltd | Education | 2019 |
| THE Band Project Limited | Other services | 2011 |
| THE Bannatyne Foundation | Administrative & support | 2019 |
| THE Bannatyne Group Limited | Arts & recreation | 2015 |
| THE Barker Property Company Limited | Real estate | 2025 |
| THE Barn Skin Limited | Other services | 2023 |
| THE Bathroom and Tile Centre Brunswick Limited | Wholesale & retail | 2024 |
| THE Beach HUT Tanning & Services Limited | Other services | 2025 |
| THE Beaumonts Service Accommodation Limited | Construction | 2022 |
| THE Beauty Club Group Limited | Other services | 2023 |
| THE Beauty Lounge (Darlington) Limited | Other services | 2010 |