| Base Camp Design and Build Limited | Construction | 2020 |
| Bassaire Limited | Extraterritorial | 1987 |
| BAT Country Brew Co Limited | Manufacturing | 2020 |
| Bates Oncology Ltd | Health & social care | 2025 |
| Bath Spinal Unit Limited | Health & social care | 2013 |
| Bath Spine Clinic Limited | Health & social care | 2015 |
| Bato Healthcare Ltd | Health & social care | 2025 |
| Batten's Boxing Limited | Arts & recreation | 2019 |
| Baybridge Architectural Joinery Limited | Manufacturing | 2000 |
| Bbanaesthetics Ltd | Health & social care | 2021 |
| Bc&A Audits Limited | Professional & scientific | 2026 |
| Bc&A Romsey Limited | Professional & scientific | 2002 |
| BDT Group Limited | Financial services | 2023 |
| BE Well Counselling Limited | Professional & scientific | 2024 |
| Beach Pearl Ltd | Real estate | 2020 |
| Bearcopy Limited | Information & communication | 2011 |
| Beat the Street (UK) Limited | Transport & logistics | 2005 |
| Beaufort Consultants Limited | Administrative & support | 2023 |
| Beaver (Improvements) Builders Limited | Construction | 2011 |
| Beck Surgical Limited | Health & social care | 2017 |
| BEE Artisan Limited | Arts & recreation | 2009 |
| Beechdean Homes Limited | Construction | 2014 |
| Beggars Fair Festivals Ltd | Administrative & support | 2025 |
| Belbins Business Park Limited | Real estate | 2000 |
| Belbins Garage Limited | Wholesale & retail | 2014 |
| Bell Street Boutique Ltd | Wholesale & retail | 2026 |
| Bella Laine Ltd | Administrative & support | 2017 |
| Bellemoor Consulting Ltd | Professional & scientific | 2016 |
| Bellevue Cars Limited | Administrative & support | 2025 |
| Bellvey Developments Limited | Construction | 2002 |
| Belmont Anaesthesia Ltd | Health & social care | 2015 |
| Benesomnus Limited | Health & social care | 2009 |
| Bentleigh Holdings Limited | Real estate | 2021 |
| Bentleigh Homes Limited | Construction | 2021 |
| Bentleigh Properties Limited | Real estate | 2021 |
| Berkshire EYE Services Ltd | Health & social care | 2019 |
| Berkshire Lower Limb Solutions Limited | Health & social care | 2009 |
| Berkshire Orthopaedics Limited | Health & social care | 2010 |
| Berkshire Shoulders Limited | Health & social care | 2014 |
| Berkshire Spine Limited | Health & social care | 2013 |
| Berties (Romsey) Ltd. | Hospitality | 2005 |
| Besthorpe Hive Limited | Manufacturing | 2021 |
| Bett Capital Ltd | Financial services | 2026 |
| Bevan and Co. Building Limited | Construction | 2016 |
| Bevan&Co. Fleet Assist Ltd | Transport & logistics | 2026 |
| Bevan&Co. Haulage Ltd | Transport & logistics | 2019 |
| Bevan&Co. Leasing Ltd | Administrative & support | 2026 |
| Bezerkergang Drinks Ltd | Manufacturing | 2020 |
| BHM Building Services Ltd | Construction | 2022 |
| Bibas Hair (Romsey) Ltd | Other services | 2018 |
| Bimetal Tools Limited | Wholesale & retail | 2015 |
| BIN 'N' Gone Waste Clearance Limited | Water & waste | 2018 |
| Birch Associates Limited | Construction | 1997 |
| Birchlands Livery Yard Ltd | Agriculture & fishing | 2003 |
| Birchwood Anaesthetic Consultants Limited | Health & social care | 2012 |
| Birdwood Ltd | Real estate | 2022 |
| Bishop Blaize Ltd | Hospitality | 2024 |
| BKP Waste & Recycling Ltd | Water & waste | 2008 |
| Black Dock Ltd | Financial services | 2024 |
| Black FOX Power Limited | Construction | 2019 |
| Black Lake Operations Ltd | Construction | 2026 |
| Blackburn & PAI Limited | Health & social care | 2003 |
| Blackmore Manor Limited | Professional & scientific | 2004 |
| Blackriver Consultancy Group Ltd | Professional & scientific | 2025 |
| Blacks Bespoke Building Ltd | Construction | 2024 |
| Blackwater Equestrian Centre Limited | Education | 2013 |
| Blackwater Equestrian Services Ltd | Wholesale & retail | 2014 |
| Blackwater Equine Limited | Wholesale & retail | 2019 |
| Blanchot Consulting Limited | Professional & scientific | 2015 |
| Bleasby Hive Limited | Manufacturing | 2021 |
| Blitz Box Limited | Professional & scientific | 2020 |
| Bloom People Limited | Administrative & support | 2011 |
| Blue ASH Limited | Real estate | 2017 |
| Blue Saint Estates Limited | Real estate | 2023 |
| Blue Steel Power Limited | Construction | 2016 |
| Blueberry Vision Ltd | Professional & scientific | 2013 |
| Bluecress Building Services Limited | Construction | 2020 |
| Bluesphere Solutions Ltd | Professional & scientific | 2010 |
| Bluewater Care Homes Limited | Health & social care | 2010 |
| Bluewater Lane Ltd | Real estate | 2023 |
| Bofinna Services Ltd | Professional & scientific | 2023 |
| Boldrift Collective Ltd | Professional & scientific | 2025 |
| Boost Home Design Ltd | Real estate | 2023 |
| Botley Roofing Group Limited | Financial services | 2025 |
| Botley Roofing Limited | Professional & scientific | 2000 |
| Botley Roofing Services Limited | Construction | 2008 |
| Bounce & Party World Ltd | Administrative & support | 2019 |
| Bournemouth and Poole Urology Limited | Health & social care | 2010 |
| Bournemouth Cardiologist Limited | Health & social care | 2012 |
| Bowditch Medical Limited | Health & social care | 2019 |
| Box Courses Limited | Health & social care | 2016 |
| Boxproc Limited | Administrative & support | 2016 |
| BPC Emea Limited | Manufacturing | 2005 |
| BPC Energy Limited | Manufacturing | 2013 |
| BR Facilities Management Ltd | Real estate | 2022 |
| Braishfield Garage Automotive Limited | Wholesale & retail | 2026 |
| Braishfield Garage Limited | Wholesale & retail | 2000 |
| Braishfield Limited | Extraterritorial | 2026 |
| Brambledown Designs Limited | Arts & recreation | 2019 |
| Brambridge House Limited | Other services | 2012 |