| Tomoyah Events Ltd | Hospitality | 2025 |
| Tone Imaging Limited | Manufacturing | 2025 |
| Tonic Fusion Limited Liability Partnership | | 2004 |
| Tool World Ltd | Wholesale & retail | 2014 |
| Top Computer Services Limited | Manufacturing | 2008 |
| Top Line 0307173 Limited | Wholesale & retail | 2007 |
| Top Medix Ltd | Health & social care | 2021 |
| Top Shelf Holdings Limited | Real estate | 2026 |
| Top Window Fixing Ltd | Construction | 2017 |
| TOP88GABI Ltd | Construction | 2015 |
| Topcom Media Limited | Other services | 2014 |
| Topnotch Acadamy UK Ltd | Education | 2019 |
| Torquemore Ltd | Information & communication | 2018 |
| Total Medical Ventures I LLP | | 2009 |
| Totality Designs Ltd | Construction | 1997 |
| Touch of Beauty Domestic Cleaning Agency Limited | Administrative & support | 2008 |
| Toyne Consulting Ltd | Health & social care | 2024 |
| TP Worldwide Trading Ltd | Real estate | 2023 |
| TR International Logistics Ltd | Transport & logistics | 2025 |
| Tranquil Care Ltd | Administrative & support | 2023 |
| Tranquil Centre Ltd | Health & social care | 2024 |
| Trans Tech Metal Scrap Ltd | Water & waste | 2019 |
| Transbogdan Limited | Manufacturing | 2016 |
| Transglobal Products Ltd | Wholesale & retail | 2010 |
| Transprotector Garage Ltd | Wholesale & retail | 2023 |
| Tranvex Ltd | Administrative & support | 2026 |
| Trass Ltd | Information & communication | 2025 |
| Treasured Hearts Ltd | Education | 2025 |
| Trent Tavern Flat Management Company Limited | Households | 2002 |
| Treymore Group Limited | Administrative & support | 2016 |
| Trifecta Group Ltd | Construction | 2026 |
| Trill Living Ltd | Wholesale & retail | 2020 |
| Trimz House Barbers Ltd | Other services | 2022 |
| Trinity Caring Services Ltd | Health & social care | 2025 |
| Tripple JE Limited | Professional & scientific | 2024 |
| Troy’S Thrift Ltd | Wholesale & retail | 2025 |
| Tru-Buy Ltd | Wholesale & retail | 2018 |
| True Disciples of Christ Ministries | Other services | 2016 |
| TS Families Production Ltd | Arts & recreation | 2026 |
| TSM P&Z Ltd | Transport & logistics | 2015 |
| TSS Health and Safety Limited | Professional & scientific | 2025 |
| Tudor House (Hatfield) Freehold Limited | Households | 2022 |
| Turbo Cleaning Ltd | Administrative & support | 2026 |
| Turkuritto Ltd | Hospitality | 2025 |
| Turmeric Group Limited | Professional & scientific | 2012 |
| Tvis Limited | Financial services | 2009 |
| Twelve Trees Park Limited | Real estate | 2026 |
| Twenty Four Technology Group Ltd | Administrative & support | 2017 |
| Twoways Investments Ltd | Real estate | 2020 |
| TY Accounting Solutions & Advisory Ltd | Professional & scientific | 2024 |
| TY Home Renovation Ltd | Construction | 2022 |
| Tyres on the Go Limited | Wholesale & retail | 2026 |
| U Ecampus Ltd | Education | 2020 |
| UA Building Construction Ltd | Construction | 2025 |
| Ubieu Ltd | Wholesale & retail | 2025 |
| UC Impact Coaching & Consulting Ltd | Professional & scientific | 2023 |
| Ueae Ltd | Construction | 2026 |
| Ugali Jiko London Ltd | Hospitality | 2024 |
| Ugogo Limited | Extraterritorial | 2015 |
| Ugold Ltd | Health & social care | 2023 |
| UH Holdings Limited | Financial services | 2007 |
| Uhsu Enterprises Limited | Wholesale & retail | 2008 |
| UK Auto Exporters Ltd | Administrative & support | 2010 |
| UK Denta Services Limited | Health & social care | 2020 |
| UK Link Estate Ltd | Real estate | 2024 |
| Ukfreshasianfood Limited | Hospitality | 2018 |
| Ultra Aluminium and Upvc Ltd | Construction | 2023 |
| Ultra Building Supplies Limited | Administrative & support | 2021 |
| Ultra Group Properties Limited | Real estate | 2025 |
| Ultra Tough Holding Ltd | Professional & scientific | 2005 |
| Ultra Tough Limited | Manufacturing | 2000 |
| Ultra Wellness Limited | Other services | 2024 |
| Ultra Windows & Bifolds Limited | Manufacturing | 2025 |
| Ultragreen Grounds Maintenance Ltd | Administrative & support | 2019 |
| Ultrasound London Limited | Health & social care | 2012 |
| Unahart Limited | Information & communication | 1984 |
| Uncle Bone TCG Ltd | Wholesale & retail | 2025 |
| Uncommon FAV Ltd | Health & social care | 2016 |
| Under the Feet Ltd | Wholesale & retail | 2019 |
| Understory Investments Limited | Real estate | 2020 |
| Unforgettable Memorials Limited | Wholesale & retail | 2021 |
| Ungana Ltd | Information & communication | 2022 |
| Unibond-Copydex Limited | Extraterritorial | 1958 |
| Unicargo Shipcraft Ltd | Transport & logistics | 2008 |
| Unicorn Projects Ltd | Construction | 2016 |
| Uniquely Drinks Ltd | Manufacturing | 2024 |
| United Buns Limited | Professional & scientific | 2026 |
| United Iraqi Medical Association | Health & social care | 2018 |
| United Knights Ltd | Arts & recreation | 2022 |
| United Kreator Solutions Ltd | Information & communication | 2023 |
| United Summit Limited | Construction | 2025 |
| Universal ENG Ltd | Manufacturing | 2026 |
| Universal Progress Company Limited | Administrative & support | 2003 |
| University of Hertfordshire Students' Union | Other services | 2011 |
| Untapped Energy Ltd | Construction | 2021 |
| Untethered UK Water Limited | Manufacturing | 2025 |
| Upskill Camp Ltd | Education | 2022 |
| Uptitek Ltd | Information & communication | 2014 |
| Urbandrift Movers Ltd | Transport & logistics | 2025 |
| US Serviced Apartments Ltd | Administrative & support | 2019 |