| UCF Properties LLP | | 2015 |
| Uchedimma Limited | Transport & logistics | 2025 |
| UCL Bricklayers Limited | Construction | 2011 |
| UCL Ltd | Manufacturing | 2002 |
| UFM Worldwide | Other services | 1932 |
| UHH Essentials Ltd | Wholesale & retail | 2020 |
| UK & Maine Ltd | Other services | 2009 |
| UK AP Services Limited | Professional & scientific | 2021 |
| UK Business Exchange Ltd | Financial services | 2017 |
| UK Cafe Limited | Hospitality | 2018 |
| UK Electronics Solutions Ltd | Construction | 2024 |
| UK Fires Direct Ltd | Construction | 2014 |
| UK Groundwork Contractors Limited | Construction | 2017 |
| UK ITF Limited | Arts & recreation | 2010 |
| UK Lightcity Ltd | Wholesale & retail | 2025 |
| UK Motor Buyer Ltd | Wholesale & retail | 2022 |
| UK Opinions Ltd | Professional & scientific | 2019 |
| UK Shared Business Services Limited | Professional & scientific | 2007 |
| UK Shogun Limited | Transport & logistics | 2011 |
| UK Toy Hunter Ltd | Administrative & support | 2018 |
| UK Trendhatch Ltd | Wholesale & retail | 2025 |
| UK Visa Appeal Limited | Professional & scientific | 2008 |
| UK Visionary Events Ltd | Arts & recreation | 2025 |
| UKHELP4U Limited | Professional & scientific | 2005 |
| Ukkf Limited | Education | 2026 |
| Ukvin Project Consulting Limited | Professional & scientific | 2016 |
| Ulcar Limited | Hospitality | 2025 |
| Ultimate Angular Limited | Information & communication | 2011 |
| Ultimate Groove Limited | Professional & scientific | 1987 |
| Ultimate Occasions Limited | Hospitality | 2019 |
| Ultra Projects Ltd | Manufacturing | 1997 |
| Ultraprecision Motion Limited | Professional & scientific | 2006 |
| Umaris Group Ltd | Information & communication | 2026 |
| Umberella Publishing Limited | Professional & scientific | 2007 |
| Umoja Healthcare Limited | Health & social care | 2017 |
| Unbound Horizon Ltd | Transport & logistics | 2026 |
| Underdog Storage Limited | Transport & logistics | 2020 |
| Underhill PUB Company Ltd | Hospitality | 2022 |
| Unfold Saunas Ltd | Arts & recreation | 2026 |
| Unhinge Limited | Wholesale & retail | 2024 |
| UNI UK Technology Limited | Wholesale & retail | 2018 |
| Uni-Build (Wiltshire) Limited | Professional & scientific | 1983 |
| Uni-Mill Services Limited | Administrative & support | 2015 |
| Unibos Limited | Wholesale & retail | 2015 |
| Unibros Property Limited | Real estate | 2022 |
| Unicoe Homes Limited | Real estate | 2025 |
| Unified Social Care Ltd | Health & social care | 2026 |
| Uniforce Production Limited | Professional & scientific | 2024 |
| Unika Aesthetics & Beauty Limited | Other services | 2023 |
| UNIQDERM1 Ltd | Wholesale & retail | 2021 |
| Unique Boutique Events (SW) Ltd | Hospitality | 2025 |
| Unique Flow Ltd | Manufacturing | 2017 |
| Unique Occasions UK Ltd | Wholesale & retail | 2025 |
| Unite Electrical Ltd | Construction | 2025 |
| Unitech Automotive UK Limited | Manufacturing | 2025 |
| United Bible Societies Association | Other services | 1988 |
| United Games Limited | Professional & scientific | 2009 |
| United Group Real Estate Limited | Real estate | 2023 |
| United Kochi Ltd | Hospitality | 2024 |
| Unity Online Network Limited | Wholesale & retail | 2018 |
| Unity Paraplanning Ltd | Financial services | 2018 |
| Unity Peak Ltd | Wholesale & retail | 2025 |
| Unity Signalling Ltd | Construction | 2026 |
| Universal Momo Ltd | Hospitality | 2020 |
| Universe Transfer Ltd | Transport & logistics | 2019 |
| Unnu Limited | Wholesale & retail | 2007 |
| Unortica Ltd | Manufacturing | 2025 |
| UP a Ladder Ltd | Construction | 2020 |
| Up:Eer Ltd | Information & communication | 2021 |
| UPC Limited | Construction | 2025 |
| Upcott CT Management Company Limited | Households | 2021 |
| Uplands Enterprise Trust | Education | 2012 |
| Uplift Living Ltd | Health & social care | 2024 |
| Upshaw Services Limited | Construction | 1998 |
| Upstream Enterprises Limited | Construction | 2005 |
| Uptodate Healthcare Group Ltd | Health & social care | 2023 |
| Upton Construction Ltd | Construction | 2010 |
| Uranus Consulting Services Limited | Information & communication | 2009 |
| Urban City Developers Ltd | Construction | 2025 |
| Urban Drive School Limited | Other services | 2009 |
| Urban Elite Swindon Ltd | Real estate | 2025 |
| Urban Gray Ltd | Construction | 2026 |
| Urban Martial Arts Schools LLP | | 2026 |
| Urban Perspective Studio Limited | Professional & scientific | 2012 |
| Urban Sensation Ltd | Wholesale & retail | 2020 |
| Urban Strides Limited | Education | 2006 |
| Urban Strides Tuition LLP | | 2012 |
| Urbangold Limited | | 1983 |
| Urbantype Projects Limited | Real estate | 1993 |
| Urszula's Driving School Ltd | Education | 2023 |
| USE Music Ltd. | Information & communication | 2018 |
| User Management Limited | Information & communication | 1999 |
| User Management Systems Limited | Information & communication | 1999 |
| Usta Barber Shop Ltd | Other services | 2026 |
| Usta Cutz Limited | Other services | 2025 |
| Utax (UK) Limited | Wholesale & retail | 1989 |
| Utilitest Software Ltd | Information & communication | 2025 |
| Utiz Ltd | Wholesale & retail | 2020 |
| Utkarshini Ltd | Information & communication | 2025 |
| Utopiana Investments Ltd | Construction | 2020 |