| Brow Formulations Limited | Other services | 2019 |
| Brown Dog Ltd | Information & communication | 2026 |
| Brown Services Ltd | Construction | 2022 |
| Browndown Limited | Arts & recreation | 2020 |
| Browning Electrical Ltd | Construction | 2023 |
| Browning Media Limited | Information & communication | 2023 |
| Browns (Isle of Wight) Limited | Hospitality | 2012 |
| Browns Town Jamdown Jerk Co Ltd | Hospitality | 2020 |
| Broyst Group Limited | Construction | 1965 |
| Bruce Cowen Furniture Agencies Ltd | Wholesale & retail | 2017 |
| Bruce Marine Services Limited | Wholesale & retail | 2026 |
| Bruk Shop Ltd | Wholesale & retail | 2024 |
| Brunel Enterprises Limited | Manufacturing | 1939 |
| Brunel Trans Ltd | Transport & logistics | 2020 |
| Brushmakers Arms Ltd | Hospitality | 2016 |
| Brydon Limited | Real estate | 1998 |
| Brytech Holdings Limited | Construction | 2020 |
| Brythanar Limited | Construction | 2024 |
| Brzrk Limited | Manufacturing | 2024 |
| BS Local Ltd | Other services | 2025 |
| BS Saman Ltd | Hospitality | 2023 |
| BSA Rational Automation Limited | Manufacturing | 1957 |
| BSA Regal Engineering Limited | Manufacturing | 1991 |
| BSA Tube Runner Limited | Manufacturing | 1980 |
| Bsa-Regal Group Limited | Professional & scientific | 1994 |
| Bsboards Limited | Manufacturing | 2003 |
| Bself Ltd | Professional & scientific | 2021 |
| BSG Group Services Ltd | Extraterritorial | 2015 |
| Bshayb Consulting Limited | Professional & scientific | 2024 |
| BSL EL Ltd | Construction | 2025 |
| Bsomp Southampton 2025 Ltd | Health & social care | 2024 |
| Bsptransport Ltd | Transport & logistics | 2025 |
| Bsqd Ltd | Professional & scientific | 2017 |
| BSR Health Recruitment Ltd | Administrative & support | 2021 |
| BSZ Properties Ltd | Real estate | 2021 |
| BT Quants Ltd | Professional & scientific | 2012 |
| BTH Services Ltd | Professional & scientific | 2020 |
| Btru Health Ltd | Health & social care | 2023 |
| Bubble and Squeak PUB Co Ltd | Hospitality | 2025 |
| Bubble Automation Limited | Information & communication | 2003 |
| Bubble Drop Limited | Hospitality | 2017 |
| Bubel Engineering Ltd | Administrative & support | 2016 |
| Bubu Logistic Limited | Transport & logistics | 2024 |
| Bubu Ruza Limited | Transport & logistics | 2015 |
| Buccia Ltd | Extraterritorial | 2022 |
| Buckingham Court (Southampton) Management Limited | Households | 1972 |
| Buckingham Gate Management Company (Southampton) Limited | Households | 1992 |
| Buckingham Property Ltd | Real estate | 2026 |
| Buckinghams of Romsey Ltd | Real estate | 2009 |
| Buckland Brown Ltd | Real estate | 2022 |
| Buckley Yacht Design Ltd | Professional & scientific | 2013 |
| Buckshot Corporation Limited | Professional & scientific | 2025 |
| Buczak Amsterdam Ltd | Hospitality | 2025 |
| Bud-E AI Ltd | Information & communication | 2025 |
| Budd Enterprise Solutions Ltd | Administrative & support | 2026 |
| Budden Holding Company Limited | Financial services | 2024 |
| Buddy Tools UK Ltd | Manufacturing | 2015 |
| Budget Castle Hire Ltd | Arts & recreation | 2018 |
| Budget Pound Plus Ltd | Wholesale & retail | 2024 |
| Bugle Hospitality Ltd | Hospitality | 2026 |
| BUI & SON Limited | Other services | 2023 |
| Build & Brick Construction Limited | Construction | 2025 |
| Build & FIX Contractors Limited | Construction | 2026 |
| Build Bright Builders Ltd | Construction | 2022 |
| Build Compliance Tech Ltd | Information & communication | 2025 |
| Buildercalc Limited | Information & communication | 2026 |
| Building Blocks Property Group Ltd | Construction | 2019 |
| Building Energy & Testing Solutions Limited | Extraterritorial | 2007 |
| Building Management and Compliance Ltd | Construction | 2024 |
| Building Regulations Consultants Limited | Professional & scientific | 1995 |
| Buildings for Life Limited | Construction | 2025 |
| Buildmydoor Supply Limited | Wholesale & retail | 2023 |
| Built to Endure Ltd | Education | 2024 |
| Builtbykim Ltd | Information & communication | 2016 |
| BUL Engineering Ltd | Manufacturing | 2021 |
| Bula Hardware Limited | Wholesale & retail | 2023 |
| Bula Market Limited | Wholesale & retail | 2024 |
| Buldent Ltd | Professional & scientific | 2023 |
| Bulk Supply Company Ltd | Professional & scientific | 2014 |
| Bullar Road Management Limited | Households | 1993 |
| Bullbear Investments Limited | Financial services | 2011 |
| Bullet Cars Limited | Transport & logistics | 2022 |
| Bullet Media Ltd | Information & communication | 2015 |
| Bulmer Engineering Consultancy Ltd | Professional & scientific | 2020 |
| Bumblebee Lighting Limited | Manufacturing | 2016 |
| Bump & Glide Ltd | Professional & scientific | 2023 |
| Bundy Services Ltd | Construction | 2019 |
| Buniyad Spice Limited | Hospitality | 2023 |
| Bunkup Ltd | Wholesale & retail | 2025 |
| Bunny Bites Ltd | Other services | 2018 |
| Bunspubs Ltd | Hospitality | 2025 |
| Bunthon Limited | Professional & scientific | 2012 |
| Buoy's Plaice Limited | Hospitality | 2016 |
| Buraq Auto Ltd | Wholesale & retail | 2024 |
| Burden Plumbing and Heating Limited | Construction | 2000 |
| Burger N Chicken Ltd | Hospitality | 2023 |
| Burgess Homes (London) Ltd | Real estate | 2022 |
| Burgess Road 334 Limited | Real estate | 2017 |
| Burgess Road Market Ltd | Wholesale & retail | 2026 |
| Burgess Williams Financial Services Ltd | Financial services | 2015 |