| Biglink Limited | Information & communication | 1994 |
| BII Properties Limited | Real estate | 2026 |
| Bike Angel Limited | Wholesale & retail | 2019 |
| Bike Boom Ltd | Wholesale & retail | 2020 |
| Bike for Life (South) C.I.C. | Education | 2011 |
| Bilginata Ltd | Wholesale & retail | 2020 |
| Bill Newman Holdings Ltd | Financial services | 2024 |
| Bill RAE Smith Limited | Information & communication | 2014 |
| Bill Starmer Painting & Decorating Ltd | Construction | 2015 |
| Billion Bottles Ltd | Administrative & support | 2014 |
| Billy Brighton Ltd | Wholesale & retail | 2026 |
| Bilston (EO & C) Training Limited | Administrative & support | 1992 |
| Binary Bear Ltd | Information & communication | 2016 |
| Binary Stars IT Services Ltd | Information & communication | 2016 |
| Bing Inventive Limited | Construction | 2011 |
| Binghams Group Limited | Real estate | 2021 |
| Binghams OFF Market Ltd | Financial services | 2019 |
| Binocle Limited | Financial services | 2018 |
| Bioberry Ltd | Wholesale & retail | 2019 |
| Biofeedback Global Health Ltd | Professional & scientific | 2021 |
| Biofeedback Healthcare Ltd | Professional & scientific | 2020 |
| Biome Bombs Ltd | Wholesale & retail | 2024 |
| Bionicmedia Limited | Information & communication | 2000 |
| Bionomica Limited | Professional & scientific | 2015 |
| Biotranslation Ltd | Professional & scientific | 2016 |
| BIP - Art Ltd | Arts & recreation | 2010 |
| Birtwell & Dorman LLP | | 2023 |
| Bishness AS Usual Ltd | Information & communication | 2023 |
| Bismuth AV Limited | Health & social care | 2022 |
| Bistro Kemptown Ltd | Hospitality | 2025 |
| Bistro Stft Ltd | Hospitality | 2025 |
| BIT by BIT Limited | Wholesale & retail | 2021 |
| BIT60 Ltd | Professional & scientific | 2011 |
| Bite Club Events Ltd | Hospitality | 2024 |
| Bite-Size Plays Limited | Extraterritorial | 2007 |
| Bits and Releases Ltd | Information & communication | 2019 |
| Bizvizion Creative Ltd | Professional & scientific | 2005 |
| Bizz Multiservices Ltd | Professional & scientific | 2020 |
| Bjde Kitchens Ltd | Hospitality | 2026 |
| BJS Homes Limited | Real estate | 2018 |
| Bjsc Ltd | Real estate | 2024 |
| Black "N" White Cat Ltd | Arts & recreation | 2019 |
| Black & Minority Ethnic Community Partnership | Health & social care | 2001 |
| Black and White Live Limited | Arts & recreation | 2010 |
| Black Anti-Racism Community Organisation C.I.C. | Professional & scientific | 2021 |
| Black Asterisk Limited | Information & communication | 2025 |
| Black Bull Films Limited | Information & communication | 2006 |
| Black Circle Pictures Ltd | Information & communication | 2023 |
| Black Flamingo Homes Ltd | Real estate | 2024 |
| Black Flamingo Management Ltd | Real estate | 2026 |
| Black Homes Ltd | Construction | 2020 |
| Black Horse PUB Ltd | Hospitality | 2025 |
| Black Horse Rottingdean Ltd | Hospitality | 2026 |
| Black Knight Southern Ltd | Construction | 2023 |
| Black Pearl Design Ltd | Professional & scientific | 2010 |
| Black Pearl Shop Limited | Wholesale & retail | 2012 |
| Black Pepper Parade Limited | Hospitality | 2025 |
| Black Pumpkin Limited | Professional & scientific | 2011 |
| Black Rock Restaurant Group Ltd | Financial services | 2017 |
| Black Rock Tyres Ltd | Wholesale & retail | 2013 |
| Black Sheep Support Limited | Information & communication | 2023 |
| Black Sheep Utilities Limited | Administrative & support | 2010 |
| Black Tourmaline Assets UK Limited | Real estate | 2017 |
| Black Tritribe CIC | Education | 2023 |
| Blackbird Film Collective Ltd | Information & communication | 2022 |
| Blackbird House Freehold Company Limited | Households | 2019 |
| Blackbriar Gates Limited | Construction | 2024 |
| Blackcat Content Ltd | Professional & scientific | 2025 |
| Blackfoot (Holdings) Ltd | Financial services | 2012 |
| Blackfoot (UK) Limited | Information & communication | 2008 |
| Blackhawk Taxis Ltd | Transport & logistics | 2022 |
| Blackpebble Ltd | Financial services | 2019 |
| Blackridge Capital Ltd | Real estate | 2019 |
| Blackspike Ltd | Information & communication | 2011 |
| Blackstardesign Ltd | Professional & scientific | 2022 |
| Blackstone Investment Management Limited | Professional & scientific | 2020 |
| Blackstone Ventures Ltd | Wholesale & retail | 2023 |
| Blackwood Creative Group Limited | Financial services | 2022 |
| Blackwood Creative Limited | Professional & scientific | 2010 |
| Blade Consulting Ltd | Professional & scientific | 2012 |
| Blank Associates Design & Advertising Limited | Professional & scientific | 2005 |
| Blanksn London Ltd | Wholesale & retail | 2020 |
| Blast Communications Limited | Arts & recreation | 1989 |
| Blast Media Ltd | Administrative & support | 2010 |
| Blast Theory | Arts & recreation | 1996 |
| Blatch Stores Ltd | Wholesale & retail | 2024 |
| Blaze Compliance Ltd | Financial services | 2026 |
| Blaze Distribution Ltd | Wholesale & retail | 2019 |
| BLB Surveyors Limited | Professional & scientific | 2002 |
| BLB Utilities Ltd | Professional & scientific | 2012 |
| Bleeding Heart Recordings Ltd | Information & communication | 2014 |
| Blencorporation Ltd | Real estate | 2016 |
| Blend Audio Limited | Information & communication | 2013 |
| Blend Catering Ltd | Hospitality | 2011 |
| Blend Coffee Co Limited | Hospitality | 2018 |
| Blend Projects Ltd | Construction | 2025 |
| Blenheim Digital Ltd | Financial services | 2016 |
| Blenheim Sealants Limited | Construction | 2006 |
| Blenheim Securities Limited | Real estate | 1977 |
| Blest Ltd | Hospitality | 2023 |