| Therecyclehub Limited | Wholesale & retail | 2025 |
| Thermal Audio Ltd | Information & communication | 2021 |
| Things Lucy Makes Ltd | Wholesale & retail | 2022 |
| Think Believe Achieve Limited | Health & social care | 2016 |
| Thodge Consulting Limited | Administrative & support | 2022 |
| Thomas Charles Landscapes Ltd | Professional & scientific | 2022 |
| Thompson Capital Management Limited | Real estate | 2015 |
| Thorney Crescent Limited | Real estate | 2025 |
| Thornhill Housing Limited | Real estate | 2021 |
| Thrimley Stud Ltd | Agriculture & fishing | 2018 |
| Thunbury Ltd | Real estate | 2019 |
| Thundridge Community Orchard Trust Limited | Agriculture & fishing | 2017 |
| Thundridge Ltd | Administrative & support | 2024 |
| Thundridge Preschool Ltd | Education | 2022 |
| Tidy Touch Transformation Ltd | Construction | 2025 |
| Tierra DEL Fuego Limited | Extraterritorial | 2023 |
| Tilt Events Ltd. | Hospitality | 2021 |
| Timber Connection Limited | Wholesale & retail | 1994 |
| TIME2DINE Ltd | Other services | 2006 |
| Timeless Salon Limited | Other services | 2026 |
| TIN LID Industrial Estate Limited | Households | 2021 |
| Tinto REX Limited | Professional & scientific | 2015 |
| TJ Property Investment Limited | Extraterritorial | 2015 |
| Tjmb CS Ltd | Professional & scientific | 2024 |
| TKB Plastering Limited | Construction | 2021 |
| Tllr Ltd | Transport & logistics | 2018 |
| Tlsm Ltd | Manufacturing | 2024 |
| TM Pharma Group Limited | Professional & scientific | 2022 |
| TMG Bill Posting Services Ltd | Administrative & support | 2013 |
| Tmtest Solutions Ltd | Information & communication | 2023 |
| TND Media Ltd | Construction | 2024 |
| Tobh Ltd | Hospitality | 2025 |
| Todd ZHU Ltd | Real estate | 2026 |
| Togometry Ltd | Wholesale & retail | 2021 |
| Tojto Ltd | Professional & scientific | 2016 |
| Toller Consulting Limited | Professional & scientific | 2014 |
| Tolz Ltd | Health & social care | 2023 |
| TOM Earle Kitchens Ltd | Manufacturing | 2024 |
| TOM Trims Real Estate Limited | Real estate | 2026 |
| Tomme Limited | Manufacturing | 2020 |
| Toms Good PUD Co Ltd | Manufacturing | 2023 |
| Top Tasty Ltd | Hospitality | 2021 |
| Top Trowel Plastering Ltd | Construction | 2024 |
| Top Wash and Car Wash Ltd | Administrative & support | 2025 |
| Topdeck Lofts Limited | Construction | 2015 |
| Torqueoutloud Ltd | Wholesale & retail | 2025 |
| Total and Complete Maintenance Limited | Construction | 2017 |
| Total Refurbishment London Ltd | Construction | 2021 |
| Touchwood Homes Limited | Construction | 2007 |
| Tower Gate MK Ltd | Households | 2024 |
| Tower Laithwaite Global Group Ltd | Administrative & support | 2026 |
| Town Mill Mews Freehold Limited | Real estate | 2012 |
| Tpmz Limited | Health & social care | 2023 |
| TR Asset Management Limited | Professional & scientific | 2018 |
| Trailventures Limited | Administrative & support | 2022 |
| Transcend Property Management Limited | Households | 2022 |
| Transcend-Uk Ltd | Transport & logistics | 2016 |
| Translate With Kate Ltd | Professional & scientific | 2018 |
| Trash 2 Go Limited | Water & waste | 2021 |
| Tree Heritage Herts Limited | Administrative & support | 2022 |
| TRH Consultancy Ltd | Information & communication | 2026 |
| Tribe Finders Group Ltd | Administrative & support | 2025 |
| Trickofthetrades Ltd | Information & communication | 2022 |
| Triform Brickwork Ltd | Construction | 2018 |
| TRU Oxygen Limited | Other services | 2025 |
| TRU Pilates Limited | Health & social care | 2025 |
| True Build & Maintenance Ltd | Construction | 2018 |
| True Dynamics Partnership Ltd | Professional & scientific | 2022 |
| Truly Amazing Cakes Limited | Manufacturing | 2012 |
| TRY Break Tours Ltd | Administrative & support | 2026 |
| TS Dragan Building Supplies Ltd | Wholesale & retail | 2018 |
| TTB Systems Ltd | Information & communication | 2015 |
| Tudor Project Solutions Limited | Professional & scientific | 2000 |
| Tumbling Bay Moorings Limited | Real estate | 2019 |
| Tuppence Halfpenny Ltd | Real estate | 2022 |
| Tuppence Ha’Penny LLP | | 2021 |
| Turnford Pipelines Limited | Other services | 1994 |
| Twenty Two Giants Ltd | Information & communication | 2023 |
| TWN Contracting Ltd | Administrative & support | 2020 |
| Two Mm's 64 Limited | Other services | 2014 |
| Two Sides Grind Ltd | Hospitality | 2023 |
| Two Twos Food - ST Albans Ltd | Hospitality | 2022 |
| Two Twos Food Ltd | Hospitality | 2020 |
| Twyford Horsemanship Centre Ltd | Education | 2018 |
| Tyne to Protect Yourself Ltd | Financial services | 2025 |
| Tyre Farm Ltd | Wholesale & retail | 2019 |
| Tyrrell Plastering Limited | Construction | 2007 |
| UK Blocks Limited | Manufacturing | 2025 |
| UK Response Ltd | Administrative & support | 2026 |
| Ukanplay Limited | Other services | 2003 |
| Unity Vape Group Limited | Wholesale & retail | 2022 |
| Universal Mobiles Limited | Wholesale & retail | 2020 |
| Universal Signs & Silk Screen Printers Ltd | Manufacturing | 2023 |
| Universe Development Limited | Professional & scientific | 2012 |
| Unlockedoor Limited | Manufacturing | 2025 |
| Urbanfine Property Management Limited | Households | 1991 |
| Utility Community Energy Scheme Stoke Limited | Energy | 2024 |
| UX Team Ltd | Information & communication | 2019 |
| V & a Developers Ltd | Construction | 2019 |
| V & J Pharmacy Limited | Wholesale & retail | 2012 |