| UK Pallet Commercial Deliveries Limited | Transport & logistics | 2014 |
| UK Potholes Ltd | Construction | 2024 |
| UK PV Limited | Energy | 2014 |
| UK Safety Solutions Limited | Administrative & support | 2010 |
| UK Select Ltd | Wholesale & retail | 2021 |
| UK Services Limited | Administrative & support | 2010 |
| UK Social Status Ltd | Other services | 2018 |
| UK Sports Bars Ltd | Hospitality | 2017 |
| UK SRM Ltd | Arts & recreation | 2014 |
| UK Trade Competitions Ltd | Transport & logistics | 2024 |
| UK Trust Loans Ltd | Financial services | 2012 |
| UK Vacuum Glass Ltd | Wholesale & retail | 2025 |
| UK Valeting Ltd | Other services | 2015 |
| UK Wind Energy Generation Limited | Energy | 2011 |
| Ukalia Ltd | Professional & scientific | 2022 |
| Ukdt Academy Ltd | Education | 2024 |
| Ukfs Group Holdings Limited | Financial services | 2020 |
| Ukfs Group Ltd | Wholesale & retail | 2006 |
| UKH Ltd | Construction | 2011 |
| Ukheatpumps Ltd | Energy | 2019 |
| Ukhg Holdings Limited | Hospitality | 2024 |
| Ukhozi Investments Limited | Health & social care | 2012 |
| UKI Life Assurance Services Limited | Extraterritorial | 1995 |
| Ukmedi Limited | Wholesale & retail | 2021 |
| Ukrsa Ltd | Arts & recreation | 2014 |
| Uksealants Ltd | Wholesale & retail | 2007 |
| Uktech Resourcing Ltd | Administrative & support | 2018 |
| Ukvisateam Limited | Administrative & support | 2025 |
| Ulaya Consulting Limited | Professional & scientific | 2021 |
| Ulfkettle Medical Ltd | Health & social care | 2020 |
| Ultimate Finish International Limited | Wholesale & retail | 2009 |
| Ultimo Electronics Limited | Wholesale & retail | 2014 |
| Ultimo Property Limited | Real estate | 2017 |
| Ultipac Ltd | Wholesale & retail | 2016 |
| Ultraroof UK Limited | Other services | 1995 |
| Ultrasnooze Ltd | Health & social care | 2009 |
| Ultros Trading Ltd | Administrative & support | 2023 |
| Umbra Energy Limited | Construction | 2022 |
| Umbra Storage Limited | Other services | 2023 |
| Umbrella Property Holdings Limited | Financial services | 2024 |
| Umbrella Property Services Ltd | Real estate | 2023 |
| Umbrella Residential Developments Limited | Real estate | 2021 |
| Umbrella Trading Limited | Wholesale & retail | 2020 |
| UMD Vape Ltd | Wholesale & retail | 2022 |
| Umii Technologies Ltd | Administrative & support | 2017 |
| Unais Group Ltd | Financial services | 2025 |
| Unbound Lands Limited | Financial services | 2025 |
| Uncanny Events Ltd | Administrative & support | 2025 |
| Under Cover Housing Ltd | Hospitality | 2020 |
| Under One Roof (East Anglia) Limited | Construction | 2014 |
| Underdog Works Ltd | Real estate | 2025 |
| Underground Location Systems (ULS) Limited | Manufacturing | 2003 |
| Underground Supplies Ltd | Wholesale & retail | 2019 |
| Underwater Consultancy Services Ltd | Mining & quarrying | 2007 |
| Underwater Technical Services Limited | Information & communication | 1992 |
| Undiscovered Montenegro Limited | Administrative & support | 2008 |
| Unearthed House Limited | Other services | 2022 |
| UNI Suppliers Ltd | Health & social care | 2011 |
| Uni-Forme Modular Systems (UK) Limited | Administrative & support | 2004 |
| Unibuild Developments Ltd | Construction | 2017 |
| Unibuild Limited | Construction | 2013 |
| Unicity Solutions Limited | Information & communication | 2012 |
| Unicorn Craft Brewing Co Limited | Manufacturing | 2017 |
| Unicorn Healthcare Limited | Health & social care | 2019 |
| Unicorn Yard (Norwich) Limited | Households | 1999 |
| Unified Payroll (Healthcare) Ltd | Professional & scientific | 2019 |
| Unified Payroll Ltd | Professional & scientific | 2015 |
| Unilake Limited | Wholesale & retail | 1993 |
| Uninformeduk Ltd | Information & communication | 2025 |
| Uninhibited Ltd | Information & communication | 2017 |
| Union of UEA Students Limited | Other services | 2015 |
| Union Street Garage Limited | Wholesale & retail | 2003 |
| Unique Adaptions Ltd | Construction | 2021 |
| Unique Domcare Limited | Health & social care | 2022 |
| Unique Professionals Group Ltd | Health & social care | 2018 |
| Unique Property's (Northampton) Ltd | Hospitality | 2010 |
| Unique Quality Products Limited | Financial services | 2024 |
| Unit 6 Elstree Building Management Company Limited | Real estate | 2009 |
| Unit Art Glass Limited | Manufacturing | 2003 |
| Unit One Curtis Road Limited | Real estate | 2014 |
| UNIT9 Digital Consulting Ltd | Financial services | 2020 |
| Unitair Limited | Real estate | 1980 |
| Unitas | Health & social care | 2008 |
| United Furniture Centre Ltd | Wholesale & retail | 2015 |
| United Generators UK Ltd | Manufacturing | 2023 |
| United Integrations Ltd | Professional & scientific | 2021 |
| United One Trading Limited | Wholesale & retail | 2021 |
| United Singh's Removal Services Ltd | Transport & logistics | 2024 |
| United Taxi App Limited | Transport & logistics | 2016 |
| Uniti Heat Ltd | Information & communication | 2022 |
| Units Housing Ltd | Real estate | 2020 |
| Unity Occupational Health and Wellbeing Limited | Health & social care | 1973 |
| Unity SEO Ltd | Professional & scientific | 2021 |
| Universal Carpentry & Building Limited | Construction | 2007 |
| Universal Concept Solutions Ltd | Construction | 2019 |
| Universal Glazing Ltd | Construction | 2022 |
| Unlimited Innovation Ltd | Information & communication | 2022 |
| Unlimited Timber Buildings Ltd | Manufacturing | 2013 |
| Unlocking Conversations Ltd | Professional & scientific | 2024 |
| Unphased Electrical Solutions Limited | Construction | 2023 |