| BMK Civils Limited | Construction | 2018 |
| Bo-Bean Ltd | Wholesale & retail | 2023 |
| Boben Logistic Ltd | Transport & logistics | 2026 |
| Body Limits Ltd | Health & social care | 2011 |
| Bodyworks Car Repair Limited | Wholesale & retail | 2015 |
| Bofaco Limited | Wholesale & retail | 2017 |
| Boilers and Aircon Milton Keynes Ltd | Construction | 2021 |
| Bolder Property Investments Limited | Real estate | 2020 |
| Book Leighton Buzzard Ltd | Wholesale & retail | 2021 |
| Bootes Investments Ltd | Professional & scientific | 2009 |
| Boro-En Properties Limited | Real estate | 1923 |
| Boroto Ltd | Wholesale & retail | 2023 |
| Botanical Hunters Ltd | Wholesale & retail | 2021 |
| Botconsultancy Limited | Hospitality | 2023 |
| Bough Homes Limited | Financial services | 2026 |
| Boujee Bougies Ltd | Manufacturing | 2022 |
| Bounce Camp Limited | Arts & recreation | 2025 |
| Bounce Recruitment Solutions Ltd | Administrative & support | 2015 |
| Bounza Ltd | Arts & recreation | 2026 |
| Bovwear Limited | Wholesale & retail | 2024 |
| Bowen Goss Limited | Professional & scientific | 2005 |
| Bowey Property Services Limited | Real estate | 2025 |
| Bowey Technical Services Ltd | Professional & scientific | 2015 |
| Bowles & Wyer Limited | Construction | 1998 |
| Bowron Classic Cars Limited | Wholesale & retail | 2014 |
| Box Clever Components Limited | Manufacturing | 2006 |
| Box to Box Limited | Professional & scientific | 2017 |
| BR Edwards Roofing Ltd | Construction | 2015 |
| Bradley-Blackburn Museum Artefact Holdings Limited | Arts & recreation | 2024 |
| Bradytct Limited | Arts & recreation | 2020 |
| Braerathy Limited | Professional & scientific | 2011 |
| Bragenham Estates Limited | Construction | 2004 |
| Brain Salad Records Limited | Information & communication | 2019 |
| Brainchunk Solutions Ltd. | Information & communication | 2017 |
| Brainscoff Ltd | Wholesale & retail | 2026 |
| Brand Basis Consultancy Limited | Professional & scientific | 2007 |
| Brand Building Co. Ltd | Professional & scientific | 2020 |
| Branko Limited | Professional & scientific | 2003 |
| Branwhite Builders Ltd | Construction | 2021 |
| Brawn Gymnastics Academy Limited | Education | 2026 |
| Bray Plastics Limited | Manufacturing | 1985 |
| Bray Plastics Trustees Limited | Professional & scientific | 2024 |
| Braycal Edinburgh Ltd | Professional & scientific | 2026 |
| BRB Media Limited | Information & communication | 2026 |
| Breakspear Medical Group Limited | Health & social care | 2025 |
| Breathe Payments Ltd | Information & communication | 2018 |
| Brecon View Eco Retreat Ltd | Hospitality | 2025 |
| Bredda Engineering Ltd | Professional & scientific | 2017 |
| BRF Property Ltd | Real estate | 2021 |
| Brian Whittle Associates Limited | Real estate | 1984 |
| Brianna Transport Ltd | Transport & logistics | 2022 |
| Briarguage Limited | Professional & scientific | 2006 |
| Brick Hill Estates Limited | Administrative & support | 2012 |
| Brickdale House Management RTM Company Limited | Households | 2023 |
| Brickhill Property Management Ltd | Households | 2025 |
| Brickly Brickwork & Construction Ltd | Construction | 2017 |
| Bridgebank Residents Association Limited | Households | 2016 |
| Bridgewater Close Management Limited | Households | 2018 |
| Bright ARC Ltd | Information & communication | 2018 |
| Bright Bay Design Ltd | Professional & scientific | 2013 |
| Bright Blue Thing Ltd | Arts & recreation | 2025 |
| Bright Nails Limited | Wholesale & retail | 1999 |
| Bright Sisters Ltd | Wholesale & retail | 2025 |
| Bright Sparky Electrical Ltd | Construction | 2024 |
| Bright Tech Ltd | Information & communication | 2014 |
| Brillinsights Ltd | Professional & scientific | 2024 |
| Brinklake Limited | Extraterritorial | 2009 |
| Bristol (UK) Limited | Manufacturing | 1992 |
| Bristol VFX Ltd | Information & communication | 2014 |
| Broadcasting Agility Ltd | Information & communication | 2019 |
| Broadoak Management Ltd | Real estate | 2007 |
| Brookes IT Management Limited | Information & communication | 2017 |
| Brooklands Academy Trust | Education | 2011 |
| Brother & Sister Group Ltd | Real estate | 2025 |
| Brown's Agricultural Machinery Company Limited | Manufacturing | 1962 |
| Browns Landscape Solutions Ltd | Administrative & support | 2014 |
| Brownstone Capital One Limited | Other services | 2026 |
| BRS Construction Services Ltd | Construction | 2026 |
| Bsdp Limited | Health & social care | 2025 |
| BSE Engineering Group Limited | Professional & scientific | 2024 |
| BSE Integrated Research & Development Limited | Manufacturing | 2024 |
| BSK Speedworks Ltd | Wholesale & retail | 2012 |
| Bsquared Events Ltd | Administrative & support | 2019 |
| BSS Interior Installations Ltd | Construction | 2020 |
| Buckingham Court Limited | Households | 2006 |
| Buckingham Engineering Mobility Systems Ltd | Manufacturing | 2002 |
| Bucks Catering Maintenance Limited | Manufacturing | 2014 |
| Bucks Chiropractic Ltd | Health & social care | 2011 |
| Bucks Ride Ltd | Agriculture & fishing | 2020 |
| Buddy Direct Ltd | Manufacturing | 2016 |
| Budziak Ltd | Wholesale & retail | 2025 |
| Buffalo Lodge Retreat Ltd | Other services | 2023 |
| Built by Board Ltd | Professional & scientific | 2024 |
| Bujorean Limited | Health & social care | 2017 |
| Bujoreanestate Ltd | Real estate | 2026 |
| Bulmor Lancer Ltd | Manufacturing | 2000 |
| Burchell Edwards (Midlands) Limited | Extraterritorial | 2008 |
| Burcott Limited | Information & communication | 2002 |
| Bure Consultancy Ltd | Professional & scientific | 2011 |
| Bureau Properties Limited | Professional & scientific | 1984 |