| Unique Vehicle Enhancements Ltd | Wholesale & retail | 2022 |
| Unique Wear UK Ltd | Wholesale & retail | 2020 |
| Unisex Hair Limited | Other services | 2005 |
| Unistay SPV Ltd | Real estate | 2024 |
| Unit Training Ltd | Education | 2023 |
| Unite Telecommunications (UK) Ltd | Information & communication | 2019 |
| United Asset Services Limited | Wholesale & retail | 2024 |
| United GAS Heating and Plumbing Limited | Construction | 2020 |
| United Law Limited | Other services | 2014 |
| United Machines Ltd | Professional & scientific | 2019 |
| United Marine Services Ltd | Manufacturing | 2017 |
| United Trans Ltd | Transport & logistics | 2017 |
| Unity & Motion Ltd | Information & communication | 2017 |
| Unity 12 CIC | Real estate | 2004 |
| Unity Build Ltd | Construction | 2018 |
| Unity Harbor Ltd | Wholesale & retail | 2026 |
| Unity Kitchens Limited | Wholesale & retail | 2026 |
| Univantage Limited | Information & communication | 2026 |
| Universal Building Projects Limited | Construction | 2020 |
| Universal Collaboration Research Ltd | Professional & scientific | 2019 |
| Universal Elite Products Ltd | Wholesale & retail | 2026 |
| Universal Exports (UK) Limited | Professional & scientific | 2009 |
| Universal Platform Ltd | Construction | 2026 |
| Universal Plumbing Supplies Limited | Wholesale & retail | 2001 |
| Universal Safety (Marine) Ltd | Transport & logistics | 2021 |
| Universal Safety Limited | Administrative & support | 2009 |
| Universal Sailing School Ltd | Arts & recreation | 2012 |
| Universal Victory Ltd | Wholesale & retail | 2026 |
| Universal Yachting Group Ltd | Financial services | 2025 |
| Universal Yachting Ltd | Administrative & support | 2007 |
| University of Southampton Retirement Scheme Trustee Limited | Extraterritorial | 2019 |
| University of Southampton Students' Union | Education | 2012 |
| Univex Group Ltd | Administrative & support | 2023 |
| Unmistakeable Fleet Cleaning Ltd | Administrative & support | 2025 |
| Unplug Ltd | Administrative & support | 2024 |
| Unruly Solutions Ltd | Information & communication | 2024 |
| Unusual Designer Gifts Ltd | Wholesale & retail | 2017 |
| Unvault Ltd | Wholesale & retail | 2026 |
| UOO Limited | Manufacturing | 2009 |
| Uorganic Limited | Wholesale & retail | 2015 |
| UP & Forward Ltd | Arts & recreation | 2019 |
| UP and Away Therapies and Consultancy Ltd | Health & social care | 2025 |
| UP Global Company Ltd | Wholesale & retail | 2015 |
| UP in Smoke Bazaar Limited | Wholesale & retail | 2018 |
| UP Supported Living LLP | | 2019 |
| Upcher & Company Limited | Administrative & support | 2002 |
| Upgrading Women Ltd | Information & communication | 2023 |
| Upham Developments Limited | Households | 2010 |
| Upham Services Limited | Construction | 2026 |
| Upiee Services Limited | Wholesale & retail | 2021 |
| UPL Corporation Limited | Wholesale & retail | 1993 |
| Upload Group Limited | Financial services | 2020 |
| Upload Media Ltd | Other services | 2015 |
| Upmill Properties Ltd | Households | 2025 |
| Upper Crust Products Limited | Real estate | 1938 |
| Uppercut Barbers and Salons Ltd | Other services | 2013 |
| Upstairs at Georges Ltd | Hospitality | 2025 |
| Upton Industrial Contracting Ltd | Construction | 2026 |
| Upton Training Ltd | Education | 2018 |
| Urban Desi Grill Ltd | Hospitality | 2025 |
| Urban Heights Access Solutions Limited | Construction | 2015 |
| Urban Professor Limited | Professional & scientific | 2019 |
| Urban Property Care Ltd | Agriculture & fishing | 2024 |
| Urban Retailers Ltd | Wholesale & retail | 2024 |
| Urbane Cars Ltd | Transport & logistics | 2026 |
| Urbanride Mechanics Ltd | Manufacturing | 2025 |
| Ursula Tavender Consulting Ltd | Professional & scientific | 2017 |
| USA Contract Consulting Limited | Information & communication | 2017 |
| USA to UK Wreaths Limited | Wholesale & retail | 2021 |
| Usayd Limited | Hospitality | 2019 |
| Usman Enterprise LI Ltd | Manufacturing | 2024 |
| UT Sail & Power Ltd | Education | 2019 |
| Utciad Ltd | Extraterritorial | 2017 |
| Uthman IBN Affan Trust | Education | 2014 |
| Utiliteq Ltd | Information & communication | 2025 |
| Utility ARB Limited | Agriculture & fishing | 2020 |
| Utility Arborists Limited | Agriculture & fishing | 2025 |
| Utonomy Ltd | Professional & scientific | 2015 |
| Utopia Digital Consultancy Ltd | Information & communication | 2022 |
| Utopia Nights Ltd | Arts & recreation | 2025 |
| Utterlicious Ltd | Wholesale & retail | 2011 |
| UVE Services Limited | Wholesale & retail | 2019 |
| Uvex Ltd | Information & communication | 2025 |
| UX Design Academy CIC | Education | 2021 |
| UX Web Solutions Ltd | Information & communication | 2022 |
| UXL Investments Limited | Information & communication | 2021 |
| V & G Sisters Ltd | Wholesale & retail | 2016 |
| V Operators Ltd | Wholesale & retail | 2018 |
| V Rodriguez Ltd | Transport & logistics | 2026 |
| V S Jain & Sons Limited | Real estate | 2022 |
| V Ventures International Ltd | Professional & scientific | 2020 |
| V&V Southampton Ltd | Transport & logistics | 2022 |
| V.I.S.M.P.R Ltd | Transport & logistics | 2019 |
| V.L.A.D. Outreach CIC | Health & social care | 2024 |
| V39 Capital Limited | Professional & scientific | 2018 |
| V8 Car Service & Repair Ltd | Wholesale & retail | 2013 |
| VA Orthopaedics Limited | Health & social care | 2021 |
| Vaasp Corporation Limited | Professional & scientific | 2021 |
| Vabe Transport Ltd | Transport & logistics | 2016 |
| Vadatech Ltd. | Wholesale & retail | 2012 |