| UK One Global Ltd | Wholesale & retail | 2024 |
| UK PAK Limited | Construction | 2025 |
| UK PEN Shows Ltd | Professional & scientific | 2007 |
| UK Pets Ltd | Information & communication | 2020 |
| UK Pizza Newcastle Limited | | 2016 |
| UK Plastic Recycling Limited | Manufacturing | 2019 |
| UK Rail Breaks Limited | Administrative & support | 2020 |
| UK Rail Contractors Limited | Other services | 2012 |
| UK Sameday Express Limited | Transport & logistics | 2015 |
| UK Service Limited | Extraterritorial | 2013 |
| UK Site Electrics Limited | Wholesale & retail | 2005 |
| UK Sourcing BD Ltd | Wholesale & retail | 2025 |
| UK Surgical Services Group Limited | Financial services | 2025 |
| UK Trade Ventures Limited | Wholesale & retail | 2022 |
| UK Traffic Signs Ltd | Manufacturing | 2026 |
| UK Truck Bodies Ltd | Manufacturing | 2015 |
| UK VAP Bankside Ltd | Other services | 2020 |
| UK VAP GPS Ltd | Hospitality | 2020 |
| UK Victory Ltd | Real estate | 2016 |
| UK Visa Advice Services Limited | Professional & scientific | 2021 |
| UK Web Services Limited | Information & communication | 2025 |
| UK Wheelchair Taxi Ltd | Transport & logistics | 2025 |
| UK Workplace Solutions Ltd | Financial services | 2012 |
| Uk.Mun Ltd | Hospitality | 2022 |
| Uk.Rb Ltd | Hospitality | 2022 |
| Uk.Rbr Ltd | Hospitality | 2022 |
| Uk.Rez Ltd | Hospitality | 2022 |
| Uk.Sr Ltd | Hospitality | 2023 |
| UK3K Limited | Real estate | 2020 |
| Uknetsec Ltd | Information & communication | 2023 |
| Ukpass Medical Education Ltd | Education | 2025 |
| Ukpizza Limited | | 2015 |
| Ukpulsedot Ltd | Wholesale & retail | 2025 |
| UKS Services Ltd | Health & social care | 2018 |
| Ukstockmarts Ltd | Wholesale & retail | 2025 |
| ULG Limited | Professional & scientific | 2009 |
| Ultimate C C Limited | Wholesale & retail | 2015 |
| Ultimate DB Limited | Health & social care | 2023 |
| Ultimate Essentia Ltd | Wholesale & retail | 2025 |
| Ultimate Limited | Wholesale & retail | 2025 |
| Ultra Lounge Limited | Hospitality | 2025 |
| Ultra Spray North East Ltd | Manufacturing | 2025 |
| Ultra Targeting Ltd | Professional & scientific | 2022 |
| Ultramap Limited | Information & communication | 2013 |
| Ultramap Monitoring Services Limited | Information & communication | 2020 |
| Ultrascan NDT Limited | Construction | 2008 |
| UMA Jammeh Ltd | Information & communication | 2025 |
| Umani Beauty Ltd | Wholesale & retail | 2025 |
| Umbilical Management Services Ltd | Mining & quarrying | 2012 |
| Umbrella Community Centre Community Interest Company | Hospitality | 2017 |
| Umer Travels & Mobile TEC Ltd | Wholesale & retail | 2016 |
| Umii Ltd | Information & communication | 2009 |
| UMK Optics Ltd | Wholesale & retail | 2025 |
| Umra Trading Limited | Wholesale & retail | 2013 |
| Umtree Ltd | Administrative & support | 2018 |
| Unas Pharm Ltd | Health & social care | 2019 |
| Unbreakable Mindset Method Ltd | Education | 2021 |
| Under Contiol Ltd | Wholesale & retail | 2025 |
| Under the Bridge Charity Limited | Hospitality | 2011 |
| Under the Rowan Trees Ltd | Wholesale & retail | 2019 |
| Understanding Value Ltd | Professional & scientific | 2018 |
| Understoreys LLP | | 2025 |
| Underwood Property Investments Ltd | Real estate | 2019 |
| Unfolding Theatre | Arts & recreation | 2008 |
| UNI Barbers NCL Ltd | Other services | 2022 |
| Uniaviaserv LP | | 2017 |
| Unicas UK Academy Limited | Education | 2025 |
| Unico Newcastle Limited | Hospitality | 2020 |
| Unicone Ltd | Information & communication | 2013 |
| Unicorn Telecoms Ltd | Information & communication | 2017 |
| Unified Telephony Solutions Limited | Information & communication | 2017 |
| Unifood Solution Limited | Hospitality | 2022 |
| Unify Group Limited | Other services | 2019 |
| Unifylinq Ltd | Information & communication | 2025 |
| Unika Group Limited | Professional & scientific | 2007 |
| Unikron Software Ltd | Information & communication | 2010 |
| Union Electric Steel UK Limited | Manufacturing | 1920 |
| Union Property Development (Haymarket) Limited | Construction | 2026 |
| Union Property Development (Hexham) Limited | Administrative & support | 1955 |
| Union Room Limited | Administrative & support | 2003 |
| Union Square (North Shields) Management Company Limited | Real estate | 1997 |
| Unionhaven Ltd | Wholesale & retail | 2024 |
| Uniphy-Therapy Limited | Health & social care | 2023 |
| Unipoint Partners Ltd | Professional & scientific | 2024 |
| Uniq Property Investment Limited | Real estate | 2019 |
| Uniq Solutions PVT Ltd | Information & communication | 2018 |
| Unique Cleaning Services North East Ltd | Administrative & support | 2021 |
| Unique Health Clubs Limited | Arts & recreation | 2017 |
| Unique Magazines Limited | Wholesale & retail | 2003 |
| Unique Property Refurbs Limited | Construction | 2020 |
| Unique Transformations NE Ltd | Construction | 2025 |
| Uniquefebby Limited | Manufacturing | 2025 |
| Uniquely U Ltd | Other services | 2023 |
| Unison Colour Holdings Limited | Manufacturing | 2025 |
| Unison Colour Pastels Limited | Manufacturing | 2025 |
| Unit 5 (NE) Ltd | Hospitality | 2025 |
| Unit SIX Development Company Ltd | Wholesale & retail | 2025 |
| Unite Communications Limited | Information & communication | 2009 |
| United Claim Solutions Ltd | Financial services | 2025 |
| United Fibre Network & Security Systems Ltd | Construction | 2025 |