| Birdlife International | Professional & scientific | 1994 |
| Birdlife LWS Limited | Professional & scientific | 1997 |
| Birdwood Holdings Ltd | Households | 2019 |
| Biscotti DI Debora Limited | Wholesale & retail | 2022 |
| Bisell Petroleum Technical Service Corporation Limited | Wholesale & retail | 2025 |
| Bishop Management Solutions Ltd | Real estate | 2004 |
| Bishop's Walk (Broad Street ELY) Management Company Limited | Households | 2000 |
| BIT Store GP Ltd | Professional & scientific | 2022 |
| BIT2QUBIT Technologies Ltd | Information & communication | 2024 |
| Bitcrunchstudio Ltd | Information & communication | 2025 |
| Bitdit Ltd | Information & communication | 2025 |
| Bite Medical Consulting Ltd | Professional & scientific | 2013 |
| Bite Street India Ltd | Hospitality | 2025 |
| Bitheim Global Limited | Financial services | 2025 |
| Bithia Limited | Agriculture & fishing | 2010 |
| Bithunter Technology Company Limited | Information & communication | 2021 |
| Bitknowledge Ltd | Information & communication | 2020 |
| Bitslice AI Ltd | Information & communication | 2024 |
| Bitstream Commerce Ltd | Wholesale & retail | 2026 |
| Bizbees Ltd | Information & communication | 2018 |
| Bizmart Shop Ltd | Wholesale & retail | 2021 |
| Bizz Trading Limited | Wholesale & retail | 2024 |
| Bjrees Marketing Ltd | Professional & scientific | 2023 |
| BJZ Property Doctors Limited | Real estate | 2017 |
| BK Camb Properties Ltd | Real estate | 2024 |
| BKW Property Management Ltd. | Real estate | 2023 |
| BL Property Development Ltd | Construction | 2021 |
| Blablabla Services Ltd | Professional & scientific | 2024 |
| Black & White Numbers LLP | | 2014 |
| Black Baltic Limited | Real estate | 2008 |
| Black Bess Limited | Manufacturing | 2014 |
| Black Box Prdcts Ltd | Wholesale & retail | 2025 |
| Black Cat Cafe Ltd | Hospitality | 2025 |
| Black Coffee Trading Ltd | Wholesale & retail | 2026 |
| Black Diamond Fibreglass Ltd | Manufacturing | 2024 |
| Black Flamingo Limited | Wholesale & retail | 2012 |
| Black Horse (2025) Ltd | Hospitality | 2025 |
| Black House Common Management Ltd | Households | 2024 |
| Black Igloo Group Limited | Information & communication | 2021 |
| Black OPS Investments Ltd | Administrative & support | 2023 |
| Black Rice VLC Limited | Hospitality | 2020 |
| Black Sheep Clothing ENG Limited | Wholesale & retail | 2023 |
| Black Sheep Composites Ltd | Manufacturing | 2025 |
| Black Tank Limited | Hospitality | 2019 |
| Black Type Ltd | Agriculture & fishing | 2004 |
| Blackbridge Corporation Ltd | Manufacturing | 2024 |
| Blackdot Solutions Ltd. | Information & communication | 2011 |
| Blacket Turner & Co Limited | Information & communication | 2009 |
| Blackford Technologies (UK) Limited | Information & communication | 2026 |
| Blackhawk Innovation Limited | Professional & scientific | 2017 |
| Blackman Agriculture Limited | Agriculture & fishing | 2004 |
| Blackman-Harris Ventures Ltd | Administrative & support | 2026 |
| Blackout Creativity on Ltd | Professional & scientific | 2020 |
| Blade AID Ltd | Other services | 2021 |
| Blakeland 1954 Limited | Extraterritorial | 2013 |
| Blakeney Garage Limited | Wholesale & retail | 2005 |
| Blaknblu Limited | Manufacturing | 2003 |
| Blanc Atelier Ltd | Other services | 2026 |
| Blanding Holdings Limited | Financial services | 2021 |
| Blank Canvas Build Ltd | Construction | 2025 |
| Blank Canvas Construction Group Ltd | Construction | 2025 |
| Blashfields Place Management Company Limited | Households | 2004 |
| Blayney Electrical Ltd | Construction | 2023 |
| Blayson - Olefines Limited | Manufacturing | 1961 |
| Blayson Casting Systems Limited | Manufacturing | 1990 |
| Blaz Global Limited | Wholesale & retail | 2026 |
| Blazing AXE Ltd | Information & communication | 2025 |
| Blazing Enamels Limited | Wholesale & retail | 2022 |
| BLE Trade Ltd | Wholesale & retail | 2025 |
| Blecon Ltd | Information & communication | 2020 |
| Bleed on IT CIC | Hospitality | 2023 |
| Bleeta.Ai LLP | | 2011 |
| Blended Learning International Ltd | Education | 2024 |
| Blended Roots Ltd | Other services | 2023 |
| Blendology Limited | Manufacturing | 2011 |
| Blenheim (Duxford) Limited | Administrative & support | 2003 |
| Blenheim Court Management Company (Cambridge) Limited | Real estate | 1974 |
| Blessedkelvinwill & Co Ltd | Other services | 2015 |
| Blessings Resolution Limited | Real estate | 2019 |
| Bleu JAY Ltd | Manufacturing | 2019 |
| Blib Studio Ltd | Information & communication | 2019 |
| Bliss International Media Co., Ltd. | Wholesale & retail | 2025 |
| Blitzen One Limited | Administrative & support | 2015 |
| BLM Trade Ltd | Arts & recreation | 2014 |
| Block and Beam Limited | Real estate | 2024 |
| Block Genie Limited | Administrative & support | 2025 |
| Blockchain Infrastructure Alliance Limited | Financial services | 2021 |
| Blockchain Marketing Solutions Limited | Other services | 2008 |
| Blockhistory Technology Limited | Manufacturing | 2021 |
| Blocks 5 and 6 Ravensworth Gardens Limited | Real estate | 2004 |
| Blocksage Engineering Ltd | Professional & scientific | 2022 |
| Blood of Angels Limited | Other services | 2017 |
| Bloodhound Books Ltd | Information & communication | 2016 |
| Bloodomics Ltd | Information & communication | 2023 |
| Bloodstock AI Ltd | Professional & scientific | 2025 |
| Bloom and Boom Limited | Manufacturing | 2025 |
| Bloom Edtech Ltd | Information & communication | 2025 |
| Bloom TEX Ltd | Wholesale & retail | 2021 |
| Bloomhall Limited | Professional & scientific | 2019 |
| Bloomsbury Cambridge Ltd. | Wholesale & retail | 2016 |