| UK Wise Security Ltd | Administrative & support | 2024 |
| UK1 Design and Build Ltd | Construction | 2025 |
| UK4YOU Consulting Ltd | Professional & scientific | 2020 |
| UKA1 Shutter Service Limited | Manufacturing | 2020 |
| Ukjp Premium Ltd | Wholesale & retail | 2020 |
| Ukrainian Books in UK Ltd | Wholesale & retail | 2025 |
| Uksecservices Ltd | Administrative & support | 2024 |
| UKT PVT Ltd | Wholesale & retail | 2020 |
| Ultimate Discount Heating Limited | Wholesale & retail | 2024 |
| Ultimate Leather Ltd | Wholesale & retail | 2020 |
| Ultimate Spray Painiting Limited | Construction | 2025 |
| Ultra Comnet Ltd | Wholesale & retail | 2024 |
| Ultra Rejuviskin Aesthetics Ltd | Administrative & support | 2017 |
| Ultraflow Support Services Ltd | Other services | 2026 |
| Ultrait Limited | Information & communication | 2009 |
| Ultraserve London Limited | Administrative & support | 2023 |
| Ultrasolutiongroup Ltd | Construction | 2025 |
| Ultratest Holdings Ltd | Manufacturing | 2018 |
| UM Solutions Ltd | Construction | 2023 |
| Umaa Ltd | Wholesale & retail | 2024 |
| Umagnus IT Ltd | Information & communication | 2026 |
| Umar Beontop Ltd | Wholesale & retail | 2024 |
| Umbraflow Payroll Ltd | Professional & scientific | 2026 |
| UMH Educational Services Ltd | Education | 2013 |
| Ummah Network | Information & communication | 2025 |
| Ummi Collection Ltd | Wholesale & retail | 2024 |
| Umrah Tours Ltd | Administrative & support | 2025 |
| Umzay Ltd | Wholesale & retail | 2026 |
| Unbor Ltd | Construction | 2022 |
| Uncu Logistic Ltd | Transport & logistics | 2024 |
| Undal Ltd | Hospitality | 2025 |
| UNH Tradings Ltd | Wholesale & retail | 2024 |
| UNI Global Consultants Ltd | Education | 2020 |
| Unicle Consulting Limited | Information & communication | 2001 |
| Unified 24 Ltd | Administrative & support | 2014 |
| Unified Access Security Consulting Ltd | Information & communication | 2026 |
| Uniglide Consultancy Limited | Education | 2026 |
| Unik Health Care Limited | Health & social care | 2018 |
| Unikey Electronics Limited | Other services | 2019 |
| Uniknex Limited | Public administration | 2024 |
| Unilag Alumni UK | Professional & scientific | 2018 |
| Unio Legal Services Ltd | Professional & scientific | 2019 |
| Unioctagon (UK) Limited | Wholesale & retail | 2011 |
| Union Pipe Limited | Manufacturing | 2015 |
| Union Portal Limited | Wholesale & retail | 2024 |
| Union UK Builders Ltd | Construction | 2024 |
| Uniq Financial Accountants Ltd | Administrative & support | 2019 |
| Uniq Property Empire Ltd | Real estate | 2022 |
| Unique Blinds Ltd | Construction | 2019 |
| Unique Design & Installations Ltd | Construction | 2018 |
| Unique Environmental Services Limited | Manufacturing | 2003 |
| Unique Home Renovations Ltd | Construction | 2021 |
| Uniqueair Limited | Arts & recreation | 2025 |
| Uniquecareagency Ltd | Administrative & support | 2021 |
| Unisupply GOV Solutions Limited | Extraterritorial | 2024 |
| Unite Property Management Limited | Real estate | 2018 |
| United Clinics Ltd | Information & communication | 2024 |
| United Distributing Company (Coin Machine Sales) Limited(The) | Administrative & support | 1984 |
| United Plumbing London Ltd | Other services | 2017 |
| United Primelink Ltd | Information & communication | 2021 |
| United Pro Tech Ltd | Administrative & support | 2019 |
| United Property Lettings Ltd | Construction | 2016 |
| Unitedcart Ltd | Wholesale & retail | 2025 |
| Unity Circle Children’S Residential Limited | Health & social care | 2026 |
| Unity City College Ltd | Education | 2025 |
| Universal Building Ltd | Construction | 2017 |
| Universal Computers Essex Limited | Information & communication | 2015 |
| Universal Services 4U Ltd | Administrative & support | 2019 |
| Universal Shisha Lounge Ltd | Hospitality | 2023 |
| Universal Supplies (International) Ltd | Transport & logistics | 2025 |
| Universal Welfare Society Limited | Health & social care | 2020 |
| Universal Wood Products Limited | Wholesale & retail | 1915 |
| Universal Wood Products Trustee Limited | Extraterritorial | 2026 |
| Univerza Ltd | Wholesale & retail | 2024 |
| Unlimited Carpentry Limited | Construction | 2022 |
| Unlocking Learners Ltd | Education | 2023 |
| UNO PM Limited | Real estate | 2019 |
| Unprovo Ltd. | Wholesale & retail | 2020 |
| Unpuzzledar Ltd | Wholesale & retail | 2024 |
| Unstoppable TAN Limited | Wholesale & retail | 2024 |
| UP to the Time Solutions Ltd | Wholesale & retail | 2023 |
| Up-Removals Services Ltd | Transport & logistics | 2019 |
| Upcycle Electronics Ltd | Wholesale & retail | 2023 |
| Updated Teck Ltd | Wholesale & retail | 2025 |
| Upford Property Limited | Administrative & support | 2006 |
| Upholstery Skills and Craft Centre Limited | Administrative & support | 2024 |
| Uplinked Security Limited | Professional & scientific | 2025 |
| Uplive Homes Ltd | Construction | 2021 |
| Uplocal Ltd | Information & communication | 2021 |
| Upminister Sandwich Ltd | Hospitality | 2026 |
| Upminster Alteration and Launderette Limited | Other services | 2023 |
| Upminster Little Learners Limited | Education | 2012 |
| Upminster Property Holdings Ltd | Real estate | 2025 |
| Upper Bedfords View Management Limited | Households | 2022 |
| Upvc Painting Pro Limited | Construction | 2023 |
| Urban Build Double Glazing Ltd | Manufacturing | 2024 |
| Urban Click Media Limited | Information & communication | 2026 |
| Urban Dryliner Ltd | Construction | 2014 |
| Urban Floors Limited | Construction | 2022 |
| Urban Grill Ventures Limited | Manufacturing | 2026 |