| Big Mouth Theatre Ltd | Administrative & support | 2017 |
| Big Mouth Theatre Schools & Events Ltd | Education | 2022 |
| Big Pineapple Ltd | Professional & scientific | 2023 |
| Big Radical Limited | Information & communication | 2009 |
| Big RIG Truck Events Ltd | Administrative & support | 2017 |
| Big Rock Estates Limited | Real estate | 2014 |
| Big Strawberry Inns Limited | Hospitality | 2006 |
| Bigal T/A the Saints PUB Ltd | Hospitality | 2025 |
| Bigger Finish Limited | Construction | 2017 |
| Bigils 3A Healthcare Limited | Health & social care | 2025 |
| Biglands Bakery Limited | Professional & scientific | 2005 |
| Bigred Media Limited | Professional & scientific | 2023 |
| Bigstrim Ltd | Information & communication | 2023 |
| Bigwood Roofing Limited | Construction | 2016 |
| Bigwoodl Limited | Wholesale & retail | 2025 |
| Bijou Baby Safety Ltd | Other services | 2023 |
| Bijou Hairdressing IW Ltd | Other services | 2012 |
| Bijou's Driving Instruction Ltd | Education | 2022 |
| Bike IT International Limited | Wholesale & retail | 2003 |
| Bikepro Servicing (BPS) Limited | Manufacturing | 2009 |
| Bilbeck Business Services Ltd | Professional & scientific | 2009 |
| Bilcan Properties Ltd | Real estate | 2026 |
| Bility Healthcare Ltd | Public administration | 2025 |
| Bill Rawles Classic Cars Limited | Wholesale & retail | 2012 |
| Bill Skailes Consulting Ltd | Professional & scientific | 2025 |
| Billa Mini Mart Limited | Hospitality | 2018 |
| Billington Carers Ltd | Health & social care | 2019 |
| Billreddin Ltd | Real estate | 2004 |
| Bills Boilers Ltd | Construction | 2020 |
| Billy Concrete Services Limited | Construction | 2012 |
| Billy Lawrance Limited | Other services | 2022 |
| Billy's Corner Limited | Administrative & support | 2017 |
| Billy's Wheels Ltd | Wholesale & retail | 2025 |
| Biltong Bokkie Ltd | Manufacturing | 2017 |
| Bimtec Electrical Ltd | Construction | 2025 |
| BIN Blitzers Ltd | Administrative & support | 2025 |
| Binaryfoundry Ltd | Information & communication | 2021 |
| Bindown Court Management Company Limited | Households | 1992 |
| Bings Domiciliary Care Limited | Health & social care | 2022 |
| Binil Ltd | Transport & logistics | 2019 |
| Binky’S Matcha Tea Limited | Wholesale & retail | 2026 |
| Binlaycourt Limited | Real estate | 1991 |
| Binti Marine Holdings Limited | Manufacturing | 2019 |
| BIO Floyds Pharma PVT Ltd | Wholesale & retail | 2023 |
| Bio-Tech Lubricants Limited | Manufacturing | 2014 |
| Bio-Wise Recovery LAB Ltd | Health & social care | 2025 |
| Biodiversity Units UK Ltd | Professional & scientific | 2023 |
| Biofynder Limited | Manufacturing | 2025 |
| Bioluminux Clinical Research Southampton Limited | Professional & scientific | 2024 |
| Biome Technologies Limited | Professional & scientific | 1984 |
| Biomedicaltech Limited | Education | 2021 |
| Biometric Access Control Systems Limited | Extraterritorial | 2007 |
| Biophilia Projects Ltd | Wholesale & retail | 2020 |
| Biopotatoes Limited | Professional & scientific | 2010 |
| Bios Inc Ltd | Administrative & support | 2020 |
| Biostatistical Foundation Limited | Professional & scientific | 2019 |
| Birak IT Limited | Information & communication | 2016 |
| Birch Hants Ltd | Transport & logistics | 2025 |
| Birchen Construction Limited | Construction | 2024 |
| Birchwood Landscapes Limited | Construction | 2012 |
| Birchwood Meadows Limited | Real estate | 2021 |
| Birthlight Teaching Limited | Education | 1999 |
| Bishop & Bishop Estates Ltd | Financial services | 2024 |
| Bishop's Waltham Private Hire Ltd | Transport & logistics | 2023 |
| Bishop's Waltham Tree Surgeons Ltd | Administrative & support | 2023 |
| Bishops Design Ltd | Construction | 2025 |
| Bishops Glade Residents Co. Limited | Other services | 1992 |
| Bishops Joinery Limited | Manufacturing | 2005 |
| Bishops Lane Management Company Limited | Real estate | 2008 |
| Bishops Waltham Care Ltd | Real estate | 2025 |
| Bishops Waltham Developments Ltd | Construction | 2021 |
| Bishopsgate Cars Limited | Administrative & support | 2025 |
| Bishopsgate Property Holdings Limited | Real estate | 2021 |
| Bishopsgate Property Investments (RS) Limited | Real estate | 2023 |
| Bishopsgate Property Lettings Limited | Construction | 2026 |
| Bishopsgate Property Nominee Ltd | Real estate | 2025 |
| Bishopsgate Property Rentals Limited | Real estate | 2023 |
| Bishopstoke Football Club Ltd | Arts & recreation | 2025 |
| Bislad Edge Limited | Wholesale & retail | 2023 |
| Bison Global Limited | Wholesale & retail | 2013 |
| Bison Industrial Group LLP | | 2013 |
| Bispo Vehicles Trading & Services Ltd | Wholesale & retail | 2024 |
| BIT Forge Interactive Ltd | Professional & scientific | 2025 |
| Bite and Brand Ltd | Wholesale & retail | 2026 |
| Bites of India Limited | Hospitality | 2023 |
| Bitmap Bureau Ltd | Information & communication | 2016 |
| Bitshift Ltd | Information & communication | 2007 |
| BITSNPIECESJ4U Limited | Wholesale & retail | 2024 |
| Bittern Construction Ltd | Professional & scientific | 2015 |
| Bittern House RTM Company Limited | Households | 2013 |
| Bitterne Care Homes Ltd | Health & social care | 2015 |
| Bitterne Community Corner Limited | Professional & scientific | 2018 |
| Bitterne Convenience Limited | Wholesale & retail | 2017 |
| Bitterne Convenience Store Ltd | Wholesale & retail | 2014 |
| Bitterne Fish and Chips Ltd | Hospitality | 2022 |
| Bitterne Hardcourts Limited | Construction | 1933 |
| Bitterne Investments Limited | Real estate | 1957 |
| Bitterne Park Barbers 1 Ltd | Other services | 2025 |
| Bitterne Properties Limited | Real estate | 2021 |
| Bitterne Road Block Management Limited | Households | 2020 |