| Ultimate Grey Ltd | Information & communication | 2024 |
| Ultimate ME Therapy Ltd | Health & social care | 2022 |
| Ultimate Skins and Stickers Ltd | Manufacturing | 2009 |
| Ultimate Styling Limited | Wholesale & retail | 2003 |
| Ultimate Towbar Systems Limited | Wholesale & retail | 2020 |
| Ultimate Underfloor Heating Solutions Ltd | Wholesale & retail | 2019 |
| Ultimate Wildlife Adventures Ltd | Administrative & support | 2018 |
| Ultra Care Clinic Limited | Health & social care | 2020 |
| Ultra Convenience Ltd | Wholesale & retail | 2025 |
| Ultra Refrigeration Limited | Manufacturing | 2004 |
| Ultra Skim Plastering Ltd | Construction | 2024 |
| Ultramart Limited | Wholesale & retail | 2025 |
| Ultramontane Consulting Ltd | Administrative & support | 2016 |
| Ulverly Portal Limited | Information & communication | 2025 |
| Umairmeo Ltd | Wholesale & retail | 2025 |
| Umami Burger Limited | Hospitality | 2023 |
| Umble Digital Limited | Information & communication | 2022 |
| Umbrella Assessment and Therapy Limited | Health & social care | 2022 |
| Umbrella Cladding Ltd | Construction | 2020 |
| Umbrella Roofing Ltd | Construction | 2020 |
| Umeabic Ltd | Wholesale & retail | 2025 |
| Umer DIN Ecom Ltd | Wholesale & retail | 2025 |
| Umiac Limited | Information & communication | 2019 |
| Ummaya CIC | Education | 2026 |
| Umptly Limited | Financial services | 2025 |
| Unage | Education | 2017 |
| Unalock Ltd | Manufacturing | 2013 |
| Unbeatable Energy Limited | Education | 2004 |
| Uncle Lin's Restaurant Ltd | Hospitality | 2020 |
| Unconventional Connections Ltd | Professional & scientific | 2016 |
| Uncorked & Uncommon Ltd | Wholesale & retail | 2025 |
| Undal Kitchen Limited | Hospitality | 2020 |
| Under One Roof Properties Ltd | Real estate | 2025 |
| Under the Influence Publishing Limited | Extraterritorial | 2008 |
| Undercard Limited | Administrative & support | 2021 |
| Undercover Holdings Limited | Financial services | 2009 |
| Undercover Roofing Supplies Limited | Wholesale & retail | 2001 |
| Undereager Ltd | Real estate | 2020 |
| Underground Construction Services Limited | Construction | 2000 |
| Underground Events Limited | Extraterritorial | 2015 |
| Understanding Politics Ltd | Education | 2010 |
| Underway Collective Ltd | Information & communication | 2026 |
| Unek Consulting Limited | Professional & scientific | 2006 |
| Unfqd Ltd | Health & social care | 2025 |
| UNI Convenience Ltd | Wholesale & retail | 2024 |
| UNI Munch Ltd | Information & communication | 2024 |
| UNI Services ( UK ) Limited | Households | 2018 |
| Uni-Quest Ltd | Education | 2013 |
| Uni-Recycle CIC | Wholesale & retail | 2024 |
| Unico Spazio Ltd | Construction | 2024 |
| Unicorn Biotechnologies Ltd | Professional & scientific | 2020 |
| Unicorn Black Ltd | Arts & recreation | 2023 |
| Unicorn Driver Recruitment Ltd | Transport & logistics | 2017 |
| Unicorn People Ltd | Administrative & support | 2019 |
| Unicus Sheffield Limited | Hospitality | 2012 |
| Unifico Limited | Information & communication | 2008 |
| Unified Business Finance Ltd | Financial services | 2022 |
| Unified Business Holdings Ltd | Financial services | 2026 |
| Unified Creative Limited | Professional & scientific | 2022 |
| Unified Goods Limited | Wholesale & retail | 2021 |
| Unihomes and Bills Limited | Information & communication | 2015 |
| Unihomes Group Limited | Financial services | 2023 |
| Unihouses Investments Ltd | Real estate | 2025 |
| Unikum LLP | | 2017 |
| Uniloy UK Limited | Financial services | 2019 |
| Unimelt Limited | Manufacturing | 2017 |
| Union & Co. Properties Limited | Hospitality | 2025 |
| Union Carbide U.K. Limited | | 1930 |
| Union Developments Limited | Construction | 1991 |
| Union Digital Initiative Ltd | Professional & scientific | 2025 |
| Union Hydraulics Limited | Manufacturing | 2012 |
| Union Nest Ltd | Wholesale & retail | 2025 |
| Union Services Limited | | 1986 |
| Union Solicitors Ltd | Professional & scientific | 2025 |
| Union Ventures Group Ltd | Manufacturing | 2026 |
| Uniplex Limited | Manufacturing | 2017 |
| Uniplex UK Trust Limited | Financial services | 2026 |
| Unique Dairies (North) Ltd | Wholesale & retail | 2016 |
| Unique Ecommerce Ltd | Wholesale & retail | 2020 |
| Unique Food and Dessert Ltd | Hospitality | 2025 |
| Unique Jewellery and Watch Limited | Wholesale & retail | 2025 |
| Unique Luxury Trader Ltd | Wholesale & retail | 2025 |
| Unique Options + Limited | Health & social care | 2020 |
| Unique Options Recruitment Ltd | Administrative & support | 2025 |
| Unique Plus Care Limited | Health & social care | 2019 |
| Unique Properties (North) Ltd | Real estate | 2023 |
| Unique Software Consultancy Ltd | Transport & logistics | 2021 |
| Unique Sushi Limited | Hospitality | 2018 |
| Unique Voyage Ltd | Wholesale & retail | 2018 |
| Unis Estates Ltd | Real estate | 2024 |
| Unison Travel Ltd | Administrative & support | 2023 |
| Unit 108 Ltd | Information & communication | 2023 |
| Unit 16 Strength and Conditioning Ltd | Arts & recreation | 2021 |
| Unit Health & Performance Ltd | Arts & recreation | 2025 |
| UNIT8 Auto Services Ltd | Wholesale & retail | 2025 |
| Unitas Facilities Management Ltd | Administrative & support | 2018 |
| Unite Martial Arts C.I.C. | Arts & recreation | 2020 |
| Unite Properties & Development Limited | Real estate | 2018 |
| United Accountants & Tax Advisors Ltd | Professional & scientific | 2022 |
| United Aquatics Limited | Wholesale & retail | 2007 |