| Uguard Ltd | Information & communication | 2023 |
| UHP Pro Ltd | Construction | 2026 |
| UHS Estates Limited | Administrative & support | 2016 |
| UHS Pharmacy Limited | Wholesale & retail | 2012 |
| Uimb Services Limited | Professional & scientific | 2014 |
| UJ Life Care (UK) Ltd | Manufacturing | 2025 |
| UK Almabrouk Marine Ltd | Professional & scientific | 2022 |
| UK Avis Ltd | Other services | 2017 |
| UK Baby Shower Co Ltd. | Administrative & support | 2015 |
| UK Baby Swim Ltd | Arts & recreation | 2017 |
| UK Bespoke Interior Co Ltd | Other services | 2016 |
| UK Bistro Ltd | Hospitality | 2024 |
| UK Conlanding Ltd | Real estate | 2024 |
| UK Directory Assistance LLP | | 2002 |
| UK Fans Legacy Ltd | Wholesale & retail | 2025 |
| UK Fight Scene Ltd | Arts & recreation | 2017 |
| UK Forklifts & Mechanical Handling Limited | Wholesale & retail | 2024 |
| UK Home Lettings Ltd | Real estate | 2025 |
| UK Kandy Limited | Administrative & support | 2018 |
| UK Kitchens and Bathrooms Ltd | Extraterritorial | 2014 |
| UK Loftsaver Ltd | Construction | 2025 |
| UK Metal Fleet Support Ltd | Manufacturing | 2025 |
| UK Motorcycle MOT Ltd | Wholesale & retail | 2019 |
| UK Neurowave Ltd | Health & social care | 2025 |
| UK Newbie Limited | Energy | 2019 |
| UK Nishikigoi Promotion Association Ltd | Other services | 2013 |
| UK Panda Properties Limited | Real estate | 2023 |
| UK Plastic Pallets Limited | Extraterritorial | 2023 |
| UK Road Services Ltd | Construction | 2023 |
| UK Robinia LLP | | 2020 |
| UK Seabed Resources Limited | Professional & scientific | 2012 |
| UK Shaolin Temple Limited | Arts & recreation | 2013 |
| UK Signature Homes Limited | Construction | 2020 |
| UK Star SP Ltd | Wholesale & retail | 2017 |
| UK Stone Imports Limited | Wholesale & retail | 2006 |
| UK Tcity Limited | Hospitality | 2022 |
| UK Tech Hub Ltd | Wholesale & retail | 2024 |
| UK Timbersolution Ltd | Manufacturing | 2021 |
| UK Web Media Limited | Information & communication | 2002 |
| UK Yuwin Travel Ltd | Administrative & support | 2026 |
| UK Zardulo Ltd | Hospitality | 2024 |
| Uk.Nguyen Investment & Letting Property Ltd | Real estate | 2021 |
| Ukasp Ltd | Information & communication | 2024 |
| UKB Plumbing Ltd | Construction | 2024 |
| UKM Holdings Ltd | Other services | 2025 |
| UKM Property Management Ltd | Other services | 2025 |
| Ukwholesalehandbags Ltd | Administrative & support | 2016 |
| Ulmo Cleaning Ltd | Administrative & support | 2020 |
| Ultima Construction Group LLP | | 2021 |
| Ultimate Carpentry Limited | Construction | 2014 |
| Ultimate Construction Logistics Ltd | Wholesale & retail | 2012 |
| Ultimate Healthcare Ltd | Manufacturing | 2006 |
| Ultimate in Car Limited | Wholesale & retail | 2002 |
| Ultimate Marine Limited | Wholesale & retail | 2010 |
| Ultimate Multi Sports Ltd | Arts & recreation | 2011 |
| Ultra Beam Lighting Ltd | Wholesale & retail | 2016 |
| Ultra I&C Limited | Manufacturing | 2022 |
| Ultra Pro MAX Limited | Wholesale & retail | 2023 |
| Ultra Smart Ltd | Wholesale & retail | 2024 |
| Ultra Softies Limited | Administrative & support | 2023 |
| Ultra-Protect Ltd | Manufacturing | 2022 |
| Ultramag Inspection Services Limited | Professional & scientific | 1977 |
| Ultraplan Limited | Extraterritorial | 2008 |
| Ulusoy 12 Ltd | Hospitality | 2026 |
| ULY Ltd | Transport & logistics | 2017 |
| Um-Ghi Products Limited | Extraterritorial | 2008 |
| Umami Southampton Limited | Hospitality | 2026 |
| Umandal Limited | Administrative & support | 2023 |
| Umatemarket Ltd | Information & communication | 2023 |
| Unan & SON Properties Ltd | Real estate | 2025 |
| Unaro Limited | Information & communication | 2020 |
| Unbound Traders Ltd | Wholesale & retail | 2019 |
| Unbranded Digital Marketing Limited | Information & communication | 2017 |
| Unbranded Vision Ltd | Wholesale & retail | 2021 |
| Underhill Construction Limited | Construction | 2018 |
| Understanding Cardiomyopathy CIC | Health & social care | 2025 |
| Underwood Aesthetics Ltd | Health & social care | 2026 |
| UNE Maison Ltd | Real estate | 2018 |
| Uneeke Technologies Limited | Extraterritorial | 2023 |
| Unexpected Places Limited | Arts & recreation | 2015 |
| Uni-Com (Global) Limited | Wholesale & retail | 1981 |
| Unibell Management Limited | Professional & scientific | 2003 |
| Uniccon Group Limited | Wholesale & retail | 2025 |
| Unicollege Limited | Wholesale & retail | 2022 |
| Unicorn Consultancy Limited | Professional & scientific | 2023 |
| Unicorn Hospitality Limited | Hospitality | 2022 |
| Unidocs Limited | Health & social care | 2016 |
| Uniflow Ltd | Wholesale & retail | 2019 |
| Unify Property Limited | Construction | 2025 |
| Union Castle House (Southampton) Limited | Households | 2022 |
| Union Crest Ltd | Wholesale & retail | 2025 |
| Union Street Holdings Limited | Real estate | 2007 |
| Uniq Code Ltd | Information & communication | 2011 |
| Unique (Southern) Ltd | Construction | 2021 |
| Unique Cars Southampton Ltd. | Wholesale & retail | 2009 |
| Unique Friends Investments Group Limited | Other services | 2020 |
| Unique Homes Property Ltd | Real estate | 2022 |
| Unique Insight Limited | Professional & scientific | 2004 |
| Unique Metalcraft Holdings Limited | Manufacturing | 2025 |
| Unique Metalcraft Limited | Manufacturing | 2018 |