| TOM Hall Consulting Limited | Administrative & support | 2015 |
| TOM Welch Consultancy Limited | Information & communication | 2017 |
| Tomato Education Limited | Education | 2025 |
| Tommyshay Investments Limited | Real estate | 2004 |
| Tony Panayides Consulting Ltd | Professional & scientific | 2015 |
| Toon Materials Limited | Construction | 2007 |
| Toots Jackson Limited | Agriculture & fishing | 2026 |
| Top Dog Communications Limited | Professional & scientific | 2018 |
| Top Guard Security Ltd | Administrative & support | 2018 |
| Top Gunz Ltd | Wholesale & retail | 2018 |
| Top Marques Repair Garage Limited | Wholesale & retail | 1999 |
| Top Real Estate Group Ltd | Households | 2019 |
| Top T Group Limited | Wholesale & retail | 2024 |
| Topguarduk Ltd | Administrative & support | 2013 |
| Topman International Limited | Wholesale & retail | 2009 |
| Toppers (Print & Design) Limited | Manufacturing | 1971 |
| Toppers Digital Limited | Manufacturing | 2006 |
| Topps Hospitality Ltd | Hospitality | 2026 |
| Torst Holdings Limited | Professional & scientific | 1998 |
| Torst Ventures Limited | Construction | 2011 |
| Total Facility Care Ltd | Administrative & support | 2017 |
| Total Global Management Services Limited | Administrative & support | 1996 |
| Total Home Solutions (Hitchin) Limited | Construction | 2024 |
| Total Mechanical Services Ltd | Construction | 2020 |
| Total Mobile Tyres Ltd | Wholesale & retail | 2016 |
| Total Self Defence Limited | Arts & recreation | 2003 |
| Tots Farm Ltd | Arts & recreation | 2024 |
| Toucan Comply Limited | Information & communication | 2018 |
| Touchline Ready Limited | Wholesale & retail | 2026 |
| Town & County Cleaning Limited | Administrative & support | 2020 |
| Town Garden Ltd | Wholesale & retail | 2017 |
| Toyota Hybrid Specialist Ltd | Wholesale & retail | 2020 |
| TP Extrusions Limited | Wholesale & retail | 2005 |
| TP Scenics Ltd | Construction | 2021 |
| TPP Projects Ltd | Professional & scientific | 2019 |
| Trade Drainage Limited | Wholesale & retail | 2023 |
| Trade Signs Direct Limited | Manufacturing | 2014 |
| Trading Machine Holdings Ltd | Information & communication | 2017 |
| Trails Financial Ltd | Financial services | 2023 |
| Training Dog Ltd | Professional & scientific | 2020 |
| Transformational Teaching LLP | | 2023 |
| Transforme UK Limited | Real estate | 2006 |
| Transparent Engineering Limited | Extraterritorial | 2000 |
| Trauma-Informed Practice UK Ltd | Professional & scientific | 2022 |
| Travel Busines Solutions Ltd | Transport & logistics | 2017 |
| Travelstay Limited | Hospitality | 2000 |
| Travelstay London Limited | Hospitality | 2018 |
| Treat YO' Self Gifts Ltd | Wholesale & retail | 2020 |
| Tree Holdings Limited | Construction | 2016 |
| Treebacks Limited | Professional & scientific | 2023 |
| Treg Caddington Ltd | Construction | 2020 |
| Treg Effingham Ltd | Construction | 2020 |
| Treg Gerrards Cross Ltd | Construction | 2020 |
| Treg Kent Ltd | Construction | 2021 |
| Treg Ripley Ltd | Construction | 2020 |
| Treg ST. Albans Ltd | Construction | 2021 |
| Treg Thorpe Ltd | Construction | 2020 |
| Treg Toddington Ltd | Construction | 2020 |
| Trenchant Technologies Limited | Information & communication | 2009 |
| Trevanion Financial Management Ltd | Financial services | 2022 |
| Trextrex Limited | Administrative & support | 2022 |
| TRG Davis Ltd | Professional & scientific | 2024 |
| TRG Financial Services Limited | Professional & scientific | 2014 |
| TRG Homes Limited | Real estate | 2023 |
| Tribe ST Ives Ltd | Arts & recreation | 2022 |
| Tribe Strength Gym Ltd | Arts & recreation | 2019 |
| Trillion Properties Investments Limited | Real estate | 2022 |
| Trillion Properties Limited | Real estate | 2018 |
| Trimar Development Limited | Real estate | 2024 |
| Trimont Trimmings Limited | Wholesale & retail | 2024 |
| Tring Developments Limited | Construction | 2016 |
| Trinity Croft Gate NO. 4 Limited | Households | 2006 |
| Trinity GAS Limited | Construction | 2021 |
| Trinity Glade Gate NO. 1 Limited | Households | 2005 |
| Trinity Glade Gate NO. 2 Limited | Households | 2005 |
| Trinity Mews (Codicote) Managementcompany Limited | Households | 2006 |
| Trinity Vale Gate NO. 8 Limited | Households | 2008 |
| Triple M UK Holdings Limited | Financial services | 2025 |
| Tritoma Consulting Limited | Professional & scientific | 2019 |
| Trudy Mcleod Ltd | Health & social care | 2023 |
| True Shades Hair Ltd | Wholesale & retail | 2026 |
| Truegents Barbers of Hitchin Ltd | Other services | 2019 |
| Trueshades Ltd | Other services | 2025 |
| Trussels Butchers Ltd | Wholesale & retail | 2013 |
| Tryax Limited | Manufacturing | 1996 |
| TS Executive Services Ltd | Administrative & support | 2025 |
| TSI Electrical Ltd | Construction | 2025 |
| TT Littlehampton Ltd | Real estate | 2026 |
| TTR Investors Limited | Professional & scientific | 2025 |
| Tudor Court Flats Limited | Households | 1989 |
| Tudor Court Management (North) Limited | Households | 1988 |
| Turbo Diesel Ltd | Transport & logistics | 2013 |
| Turbodrive Ltd | Wholesale & retail | 2025 |
| Turcuisine Group Holdings Limited | Financial services | 2020 |
| Turner Howie Limited | Professional & scientific | 2017 |
| Turners Electrical Contractors Ltd | Construction | 2023 |
| TUS Umbrella Limited | Professional & scientific | 2015 |
| Tutor Doctor Hitchin & Stevenage Limited | Education | 2017 |
| Tutors Together Ltd | Administrative & support | 2024 |
| TW Flooring Group Ltd | Construction | 2015 |