| Black Dog Productions Limited | Information & communication | 2011 |
| Black Eagle International UK Ltd. | Manufacturing | 2016 |
| Black Girls Booked Ltd | Other services | 2022 |
| Black Glass Comms Ltd | Information & communication | 2019 |
| Black Horse at Chippenham Ltd | Hospitality | 2025 |
| Black Ivory Ltd | Manufacturing | 2020 |
| Black LAB Designs Ltd | Professional & scientific | 2018 |
| Black Meadow Letting Ltd | Real estate | 2025 |
| Black Meadow Property Group Limited | Construction | 2023 |
| Black Mothers Matter CIC | Education | 2020 |
| Black Pearl Capital Management Ltd | Financial services | 2019 |
| Black Peppers Whitchurch Limited | Hospitality | 2024 |
| Black PIG Pizza Co Ltd | Hospitality | 2025 |
| Black Piper Limited | Administrative & support | 2023 |
| Black Piste Consulting Ltd | Professional & scientific | 2020 |
| Black Pixel Limited | Education | 2011 |
| Black Porcelain Investments Ltd | Financial services | 2020 |
| Black Series Group Limited | Wholesale & retail | 2019 |
| Black Series Limited | Wholesale & retail | 2016 |
| Black Sheep Bars Limited | Hospitality | 2001 |
| Black Sheep Tattoo Ltd | Other services | 2021 |
| Black South West Network | Administrative & support | 2005 |
| Black Street Works Ltd | Professional & scientific | 2007 |
| Black Swan MEG Limited | Hospitality | 2010 |
| Black Timber Limited | Professional & scientific | 2023 |
| Black Turtle Consulting Ltd | Information & communication | 2019 |
| Black Welsh Mountain Sheep Breeders' Association | Agriculture & fishing | 1922 |
| Black Women LET Loose Theatre Company CIC | Education | 2020 |
| Blackart Management Limited | Professional & scientific | 2016 |
| Blackberry Building Limited | Construction | 2024 |
| Blackberry Cottage Holidays Ltd | Hospitality | 2020 |
| Blackberry Management Ltd | Real estate | 2022 |
| Blackbird Property Ltd | Real estate | 2023 |
| Blackbolt Enterprises Ltd | Extraterritorial | 2020 |
| Blackbox Building Services Ltd | Construction | 2025 |
| Blackburn Community Radio Limited | Wholesale & retail | 2017 |
| Blackcore Technologies Ltd | Manufacturing | 2023 |
| Blackcrest International Ltd | Wholesale & retail | 2026 |
| Blackdog Energy and Services Ltd | Real estate | 2019 |
| Blackfields Furniture Ltd | Manufacturing | 2014 |
| Blackfin Media Ltd | Administrative & support | 2018 |
| Blackfish Engineering Design Limited | Professional & scientific | 2016 |
| Blackhorse Construction Limited | Construction | 2000 |
| Blackhorse Lane Management Company Limited | Households | 2003 |
| Blackhorse Place Ltd | Real estate | 2019 |
| Blackhorse Tiling Contractors Ltd | Construction | 2017 |
| Blacklight Productions Limited | Information & communication | 2015 |
| Blackmaple Limited | Professional & scientific | 2014 |
| Blackmore & Langdon Limited | Agriculture & fishing | 1963 |
| Blackmore Chauffeurs Limited | Transport & logistics | 2023 |
| Blackmore Down Management Company (Shaftesbury) Limited | Real estate | 2019 |
| Blackmore Head Ltd | Real estate | 2007 |
| Blackmore Services Limited | Real estate | 2020 |
| Blacknore Consulting Ltd | Information & communication | 2021 |
| Blackpoint IT Limited | Information & communication | 2011 |
| Blackpoint Lettings Limited | Real estate | 2016 |
| Blackrock Investments Limited | Financial services | 1981 |
| Blackrock Marble Co. Ltd. | Construction | 2007 |
| Blackrockprop Limited | Construction | 2013 |
| Blacksand Capital UK Limited | Professional & scientific | 2022 |
| Blackshield Protection Group Ltd | Administrative & support | 2026 |
| Blackstable Limited | Financial services | 2010 |
| Blackstar Property Solutions Limited | Real estate | 2023 |
| Blackstone Chauffeurs Ltd | Transport & logistics | 2022 |
| Blackstone Energy Group Ltd | Other services | 2025 |
| Blackstone Living Ltd | Real estate | 2025 |
| Blackstory Entertainment Ltd | Information & communication | 2012 |
| Blackstowe Ltd | Extraterritorial | 2026 |
| Blackswarth House Limited | Households | 1984 |
| Blacktide Partners Ltd | Professional & scientific | 2024 |
| Blackwell Hydraulics Limited | Extraterritorial | 1979 |
| Blackwell Martin John 80007 Limited | Transport & logistics | 2014 |
| Blackwell Surveying Ltd | Professional & scientific | 2026 |
| Blackwood Landscapes Ltd | Administrative & support | 2022 |
| Blackz Property Group Ltd | Construction | 2023 |
| Blade Zone Barber Ltd | Other services | 2024 |
| Bladeless BIN the Blade CIC | Education | 2024 |
| Bladen Commercial Property Consultants Ltd | Real estate | 2013 |
| Bladon & COX Ltd | Hospitality | 2018 |
| Blagdon IT Limited | Information & communication | 2008 |
| Blagdon Tree Surgeons Limited | Agriculture & fishing | 2020 |
| Blagdon Valley GUN Club Limited | Arts & recreation | 2004 |
| Blagdon Valley Minibus Association | Transport & logistics | 1995 |
| Blagford Developments Ltd | Construction | 2016 |
| Blagford Properties Limited | Real estate | 2000 |
| Blagsaey Arts CIC | Arts & recreation | 2020 |
| Blaircourt Equine Veterinary Clinic Limited | Professional & scientific | 2009 |
| Blaise Care Limited | Health & social care | 2024 |
| Blaise Consulting Ltd | Information & communication | 2025 |
| Blaise Dell Brickworks Limited | Construction | 2003 |
| Blaise Dell Flat Management Co. Limited | Households | 1973 |
| Blaise Ltd | Construction | 2005 |
| Blak Wave Productions Ltd | Information & communication | 2020 |
| Blake Elearning UK Limited | Education | 1987 |
| Blake Joinery Company Limited | Manufacturing | 1989 |
| Blake Roofing SW Ltd | Construction | 2025 |
| Blake Sports Activation Limited | Professional & scientific | 2025 |
| Blake Veterinary Group Limited | Extraterritorial | 2005 |
| Blakeborough Ltd | Professional & scientific | 2007 |
| Blakes Construction (SW) Limited | Construction | 2025 |