| BKS Utilities Limited | Construction | 2023 |
| Bktd Limited | Professional & scientific | 2024 |
| Bkupe Care Limited | Health & social care | 2019 |
| BL Bars Ltd | Hospitality | 2022 |
| BL Convenience Store Ltd | Wholesale & retail | 2025 |
| BLA Consultancy Limited | Hospitality | 2020 |
| Blabla Ltd | Wholesale & retail | 2020 |
| Blac Holdings Limited | Real estate | 2018 |
| Black & Decker Batteries Management Limited | Professional & scientific | 1988 |
| Black & White Financial Solutions Ltd | Financial services | 2012 |
| Black Brick Holdings Limited | Real estate | 2026 |
| Black Cat Aero Services Limited | Professional & scientific | 2025 |
| Black Deaf UK C.I.C. | Education | 2025 |
| Black Diamond-Uk Ltd | Wholesale & retail | 2017 |
| Black Dog Properties Limited | Real estate | 1999 |
| Black Family 1 Limited | Construction | 2020 |
| Black Family Holdings Ltd | Construction | 2019 |
| Black Health Initiative (BHI) | Public administration | 1996 |
| Black Horse PUB (Chesham Vale) Ltd | Hospitality | 2026 |
| Black KAT HR Ltd | Administrative & support | 2019 |
| Black Label Competitions Limited | Administrative & support | 2022 |
| Black Label Vehicle Sales Limited | Wholesale & retail | 2019 |
| Black Line Distribution Ltd | Wholesale & retail | 2019 |
| Black Lion (Bramley) Limited | Hospitality | 2017 |
| Black Lodge Holdco Limited | Information & communication | 2023 |
| Black Lodge Limited | Information & communication | 2014 |
| Black Mill Studio Ltd | Professional & scientific | 2020 |
| Black Night Bay Horse Limited | Hospitality | 2025 |
| Black Night Holdings Ltd | Real estate | 2019 |
| Black Night Orangery Ltd | Manufacturing | 2019 |
| Black Night Trading Ltd | Hospitality | 2019 |
| Black Pepper Creations Limited | Hospitality | 2014 |
| Black Product Consultancy Ltd | Professional & scientific | 2025 |
| Black Star Certification Limited | Professional & scientific | 2020 |
| Black Star Motorsport Ltd | Manufacturing | 2022 |
| Black Swan (Leeds) Limited | Hospitality | 2024 |
| Black&White Solutions Ltd | Transport & logistics | 2016 |
| Blackabey's Happy Skin Company Limited | Health & social care | 2024 |
| Blackbox Creative Limited | Information & communication | 2013 |
| Blackbox Monitoring Systems Limited | Professional & scientific | 2015 |
| Blackboxed Solutions Ltd | Information & communication | 2016 |
| Blackcastle Properties Ltd | Real estate | 2018 |
| Blackdice Cyber Limited | Information & communication | 2019 |
| Blackfriars Insurance Brokers Limited | Financial services | 1995 |
| Blackgate Asset Management Ltd | Real estate | 2024 |
| Blackgate Property Limited | Households | 2024 |
| Blackgates Developments Limited | Construction | 2013 |
| Blackhat Creative Limited | Arts & recreation | 2015 |
| Blackhold Protection Limited | Administrative & support | 2025 |
| Blackman Alcohol Ltd | Wholesale & retail | 2024 |
| Blackmoor Films Limited | Information & communication | 2012 |
| Blackmoss Ltd | Real estate | 2025 |
| Blackpool Markets Limited | Extraterritorial | 1992 |
| Blackrock Contractors Ltd | Mining & quarrying | 2026 |
| Blacks Affinity Limited | Professional & scientific | 2014 |
| Blacks Connect Limited | Extraterritorial | 2012 |
| Blacks Solicitors LLP | | 2004 |
| Blacks Trustees Limited | Professional & scientific | 2004 |
| Blackspace Media Ltd | Wholesale & retail | 2011 |
| Blackstilt Limited | Real estate | 2011 |
| Blackstone Estates (Yorkshire) Ltd | Real estate | 2015 |
| Blackstone Investment (Yorkshire) Ltd | Real estate | 2020 |
| Blackstone Lighting Limited | Wholesale & retail | 2012 |
| Blackstone Property Lets Ltd | Real estate | 2016 |
| Blackstone Tax Limited | Professional & scientific | 2023 |
| Blackstory Limited | Wholesale & retail | 2025 |
| Blackthorn Consulting UK Limited | Professional & scientific | 2017 |
| Blackthorn Defence & Research Limited | Professional & scientific | 2025 |
| Blackthorn IT Advisory Limited | Information & communication | 2025 |
| Blackthorn Projects Ltd | Construction | 2020 |
| Blacktop Surfacing Limited | Construction | 2006 |
| Blackwell Financial Solutions Ltd | Financial services | 2020 |
| Blackwell Mortgage Solutions Limited | Financial services | 2022 |
| Blackwire Intelligence Ltd | Information & communication | 2022 |
| Blackwood House Property Management Company Limited | Households | 2023 |
| Blackwood Private Reserve Limited | Wholesale & retail | 2026 |
| Blackwoods Medical Ltd | Health & social care | 2014 |
| Blackxray Tech Ltd | Information & communication | 2025 |
| Blade Public Relations Limited | Professional & scientific | 1996 |
| Blair Roofing Limited | Construction | 2025 |
| Blairfettie Estate Forests LLP | | 2020 |
| Blake Henry's Family Butchers Ltd | Wholesale & retail | 2024 |
| Blake Marketing Limited | Administrative & support | 2001 |
| Blakewood Estates Ltd | Real estate | 2024 |
| Blakewood Holdings Ltd | Real estate | 2025 |
| Blakewood Landscapes Ltd. | Administrative & support | 1999 |
| Blanc Digital Limited | Administrative & support | 2025 |
| Blanc Studios Leeds Limited | Other services | 2025 |
| Bland and Swift Limited | Professional & scientific | 1993 |
| Bland Media Limited | Professional & scientific | 2026 |
| Blankson Consulting Limited | Administrative & support | 2020 |
| Blankson Enterprises Limited | Information & communication | 1996 |
| Blast Cleaning & Maintenance Ltd | Administrative & support | 2009 |
| Blast Digital Ltd | Professional & scientific | 2021 |
| Blast Radius Films Ltd | Arts & recreation | 2025 |
| Blast-Tech Limited | Construction | 2026 |
| Blastoise Brokers Limited | Wholesale & retail | 2025 |
| Blastwave Limited | Construction | 2012 |
| Blawhurst Limited | Hospitality | 1971 |
| Blaxmill (Thirty-Eight) Limited | Real estate | 2004 |