| TKC Research Limited | Real estate | 1992 |
| TLM Underfloor Heating Company UK Ltd | Construction | 2022 |
| TLS Property Services Ltd | Construction | 2017 |
| TLU Contracts Limited | Construction | 2011 |
| TM Development Services Limited | Construction | 2019 |
| TNK Builders Ltd | Construction | 2022 |
| TNS Property Limited | Real estate | 2018 |
| TO the Top Touring Limited | Other services | 2010 |
| Toboss Ltd | Administrative & support | 2009 |
| Todcon Ltd | Construction | 2018 |
| Toelvuverkfraedingur Ltd | Information & communication | 2015 |
| Tolworth Development Limited | Real estate | 2017 |
| Tomall Management Ltd | Professional & scientific | 2017 |
| Tomas Property Ltd | Real estate | 2025 |
| Tomimi LLP | | 2012 |
| Tonasia Ltd | Information & communication | 2025 |
| Tone Group Trustee Limited | Administrative & support | 2024 |
| Tony's PIE and Mash Services Ltd | Hospitality | 2021 |
| Top Advertising Limited | Professional & scientific | 2012 |
| Top Curries Ltd | Hospitality | 2019 |
| Top Floor (London) Ltd | Other services | 2015 |
| Top House Limited | Extraterritorial | 1997 |
| Top Notch Roofing Services Ltd | Construction | 2019 |
| Toquin Contracts Ltd | Construction | 2017 |
| Toquin SA Limited | Construction | 2000 |
| Tori Gaynor Ltd | Education | 2020 |
| Total Cleaning & Maintenance Limited | Administrative & support | 2012 |
| Total Football Mania Ltd | Arts & recreation | 2013 |
| Total Plumbing & Heating (Enfield) Limited | Wholesale & retail | 2020 |
| Totally Flooring Essex Limited | Construction | 2026 |
| Totalworth Building Solutions Ltd | Construction | 2021 |
| Totleigh LLP | | 2012 |
| Tots & Hops Gymnastics Ltd | Health & social care | 2016 |
| Tots to Teens Shoe Lounge Limited | Wholesale & retail | 2014 |
| Touch of Resin Ltd | Wholesale & retail | 2022 |
| Touch Tuina (UK) Limited | Health & social care | 2013 |
| Touch Tuina (York) Limited | Health & social care | 2014 |
| Tovey Partners LLP | | 2017 |
| Tower Road (Epping) Limited | Real estate | 2014 |
| Towerflow Properties Limited | Real estate | 2003 |
| Town Square (Erith) Management Company Limited | Households | 2004 |
| TPC Media Limited | Information & communication | 2025 |
| TR Collier & Associates Limited | Professional & scientific | 1999 |
| Trad Properties LLP | | 2011 |
| Trad Trustees Limited | Professional & scientific | 2000 |
| Trade Mark Wizards Limited | Professional & scientific | 2012 |
| Tradefund Investments Limited | Construction | 1998 |
| Tradelinkai Ltd | Information & communication | 2026 |
| Tradeprint London Limited | Administrative & support | 2011 |
| Traders LAB Limited | Wholesale & retail | 2020 |
| Trading Grapes Ltd | Wholesale & retail | 2026 |
| Trakia Foods Ltd | Wholesale & retail | 2025 |
| Trakia London Ltd | Wholesale & retail | 2025 |
| Trans Top Ltd | Transport & logistics | 2025 |
| Transformatech Limited | Information & communication | 2025 |
| Transhorn Limited | Real estate | 1997 |
| Transnom Limited | Transport & logistics | 2017 |
| Transport Media Technologies Ltd | Information & communication | 2021 |
| Transported Care Limited | Other services | 2026 |
| Travelled Road Interiors Ltd | Wholesale & retail | 2018 |
| Treeline Construction Limited | Construction | 2022 |
| Treend Construction Limited | Administrative & support | 2007 |
| Treetops Property Limited | Real estate | 2006 |
| Treevend Limited | Wholesale & retail | 2025 |
| Trelane Services Ltd | Other services | 2022 |
| Trending NOW Media Limited | Information & communication | 2021 |
| Trendy Loft Conversions Ltd | Construction | 2013 |
| Trendz Champar Ltd | Real estate | 2025 |
| Trendz Global Limited | Administrative & support | 2015 |
| TRI Capital R Limited | Real estate | 2024 |
| TRI Arlington Limited | Construction | 2024 |
| TRI CAP ST Limited | Real estate | 2024 |
| TRI Capital B Limited | Real estate | 2024 |
| TRI Capital BG Limited | Construction | 2023 |
| TRI Capital BW Limited | Construction | 2022 |
| TRI Capital CH Limited | Construction | 2022 |
| TRI Capital Corporation Limited | Construction | 2015 |
| TRI Capital Corporation NV Limited | Construction | 2020 |
| TRI Capital CVL Limited | Real estate | 2024 |
| TRI Capital DS PV Limited | Real estate | 2016 |
| TRI Capital EC Limited | Construction | 2023 |
| TRI Capital KT Limited | Real estate | 2025 |
| TRI Capital LET Limited | Real estate | 2025 |
| TRI Capital Nottingham Limited | Construction | 2020 |
| TRI Capital OS Limited | Construction | 2022 |
| TRI Capital Port Limited | Real estate | 2024 |
| TRI Capital PV Limited | Construction | 2026 |
| TRI Capital R4 Limited | Construction | 2026 |
| TRI Capital R5 Limited | Construction | 2026 |
| TRI Capital R6 Limited | Real estate | 2026 |
| TRI Capital Shepherds Bard Limited | Real estate | 2015 |
| TRI Capital T Limited | Real estate | 2025 |
| TRI Capital TNV Limited | Real estate | 2025 |
| TRI Capital V Limited | Construction | 2022 |
| TRI Capital V2 Limited | Real estate | 2022 |
| TRI Citi CR Limited | Real estate | 2024 |
| TRI Jade Limited | Real estate | 2025 |
| TRI Peter Limited | Real estate | 2024 |
| TRI Tuatha Investment Management Limited | Professional & scientific | 2024 |
| Trialsound Limited | Real estate | 1981 |