| Tomori E&P Limited | London | 2009 |
| Tomtechs Services Limited | Aberdeen | 2019 |
| Tonfanau Ltd | Llwyngwril | 2025 |
| Tongkah Harbour TIN Dredging Limited | London | 2025 |
| Tongue Electrical Commissioning Services Ltd | Montrose | 2014 |
| Tony’S Lifting Ltd | Beverley | 2026 |
| Top Management Ltd. | Alford | 1995 |
| Top Side & SUB Sea Solutions Ltd | Fleetwood | 2023 |
| Toprock Training Limited | Barnsley | 2017 |
| TOPSOIL2U Limited | Farnham | 2021 |
| TOR Drilling (UK) Limited | | 1999 |
| Torfaen Aggregates Limited | Bargoed | 2025 |
| Torpoint Capital Ltd | Lichfield | 2021 |
| Torr Geophysical Consulting Limited | Lamberhurst | 2001 |
| Torrance Subsea Limited | Aberdeenshire | 2007 |
| Torridon Investments Ltd | Malvern | 2006 |
| Torrington Stone Limited | Exeter | 1985 |
| Torryburn Data Services Ltd | Inverurie | 2024 |
| Tortek Total Ltd | London | 2026 |
| Total Abseil Solutions Limited | Dunfermline | 2013 |
| Total Akcess Limited | Telford | 2017 |
| Total E&P Aktobe Limited | London | 2014 |
| Total Graphite PLC | London | 2017 |
| Total Services Management (TSM) Ltd | Frinton-On-Sea | 2020 |
| Total Way Logistics Ltd | Wembley | 2018 |
| Totalenergies E&P International K1 Limited | London | 2015 |
| Totalenergies E&P International K2 Limited | London | 2015 |
| Totalenergies E&P International K3 Limited | London | 2015 |
| Totalenergies E&P Resources UK Limited | London | 1996 |
| Totus Subsea Solutions Ltd | Montrose | 2012 |
| Toucan Engineers Limited | Great Yarmouth | 1995 |
| Touch of Fame (TOF) Ltd | London | 2020 |
| Touche Consulting Limited | Harrow | 2001 |
| Touchstone Geological Services Limited | Swindon | 2018 |
| Tough Access Ltd | Laurencekirk | 2024 |
| Tower Colliery Limited | Aberdare | 1994 |
| Tower Funding Management Limited | London | 2025 |
| Tower Regeneration Limited | Durham | 2009 |
| Towy Sand & Gravel Limited | Dyfed | 1981 |
| Tracey Flynn Ltd | Montrose | 2020 |
| Tracs International Limited | Aberdeen | 1997 |
| Trade Workshop Ltd | London | 2022 |
| Traditional Granite (Cornwall) Limited | Liskeard | 2026 |
| Tradstocks Stone Quarrying Ltd. | Stirling | 2007 |
| Trafalgar OIL & GAS Limited | London | 2015 |
| Trainor Technical Services Limited | Middlesbrough | 2015 |
| Trans Asia Energy Services (UK) Ltd | Aberdeen | 2019 |
| Trans Eco Minerals and Mining Ltd | Windsor | 2012 |
| Trans European OIL & GAS Limited | London | 2015 |
| Trans World Fuels Ltd | Baldock | 2012 |
| Trans-Afrique Services Ltd | Stockport | 2023 |
| Trans-Siberian Gold Limited | Milton Keynes | 1972 |
| Transarca Limited | Potters Bar | 2003 |
| Transcendentia Mining Limited | Stockport | 2024 |
| Transition Clean Solutions Limited | Banchory | 2020 |
| Transition Commodities Ltd | Hampshire | 2021 |
| Transminerals (UK) Limited | Northampton | 2016 |
| Transocean Onshore Support Services Limited | Aberdeen | 2001 |
| Transocean UK Limited | Birmingham | 2000 |
| Transtip Limited | Bromsgrove | 2021 |
| Transtrade Commodities (UK) Ltd | London | 2023 |
| Transunion Petroleum Limited | Bath | 2009 |
| Transweld International Drilling Services Limited | Cardiff | 1998 |
| Transworld Petroleum (U.K.) Limited | London | 1971 |
| Travis International Drilling Limited | Newbury | 2013 |
| Traxx (Aggregates) Limited | Birmingham | 2009 |
| Traynorrov Limited | Dundee | 2018 |
| Trcs Consulting Ltd | Barnet | 2021 |
| Treadstone Mining Services Ltd | London | 2024 |
| Treasure Island Resources Limited | Heathfield | 2017 |
| Trecarne Quarry Limited | Cornwall | 2004 |
| Trefigin Quarries Limited | Aberteifi | 1984 |
| Trefor Quarry Limited | Carnarfon | 2015 |
| Tregunnon Quarry Limited | Birmingham | 1995 |
| Trenam Engineering Limited | Worksop | 2021 |
| Treo Minerals Ltd | London | 2021 |
| Triangle Energy (UK) PTY Ltd | London | 2023 |
| Trident Access Ltd | Dunfermline | 2021 |
| Trident Energy Management Limited | London | 2016 |
| Trinity Exploration & Production Limited | Reading | 2011 |
| Trinnitech U.K. PVT. Ltd. | Harrow | 2017 |
| Triton Marine & Engineering Consultants Limited | Aberdeen | 2017 |
| Triton Marine Services Limited | Aberdeen | 2018 |
| Triton Subsea Ltd | London | 2026 |
| Tropical Seismics Ltd | London | 2002 |
| Tropics Energy UK Limited | London | 1997 |
| TRT Minerals Ltd | London | 2025 |
| TRU Henham Quarry Limited | Ipswich | 2026 |
| True North Marine Ltd | Aberdeen | 2019 |
| Trung HA Building Materials Co., Ltd | Beckenham | 2022 |
| Tryal Electronics Limited | Arbroath | 1986 |
| TS5 Enterprise Limited | Stockton-On-Tees | 2022 |
| Tsafrika Ltd | Bristol | 2023 |
| TSL Technology Limited | Eastleigh | 1992 |
| TT Inspection Ltd | Aberdeen | 2024 |
| TTT Green Life Ltd | London | 2022 |
| Tudor Griffiths Limited | Ellesmere | 2008 |
| Tudor Hall Energy Europe Limited | Llandysul | 2014 |
| Tudor Hall Energy Limited | Llandysul | 2009 |
| Tudor Industries Limited | London | 2018 |