| BG Construction and Plant Ltd | Administrative & support | 2018 |
| BGC Sussex Ltd | Construction | 2023 |
| BGD One Ltd | Real estate | 2018 |
| BGM Leisure Limited | Real estate | 2013 |
| BH Price Realty Ltd | Real estate | 2021 |
| Bhatthal Properties Limited | Real estate | 2024 |
| BHP Global Limited | Professional & scientific | 2007 |
| BI Developers Limited | Information & communication | 2012 |
| Bibby's Beans Festivals Ltd | Hospitality | 2024 |
| Bibby's Beans Ltd | Hospitality | 2024 |
| BIC UK North Ltd | Administrative & support | 2020 |
| Bickford Building and Civil Engineering Ltd | Construction | 2022 |
| Bidder Care Ltd | Health & social care | 2025 |
| Bierspool Cycles Limited | Wholesale & retail | 2015 |
| Big Apple Ltd | Wholesale & retail | 2005 |
| Big Box Enterprises Ltd | Professional & scientific | 2023 |
| Big Meadow CSA Ltd | Agriculture & fishing | 2022 |
| Big Picture Concepts Limited | Information & communication | 2004 |
| Big Sky Technical Consultancy Ltd | Agriculture & fishing | 2024 |
| Big Spuds Ltd | Hospitality | 2021 |
| Big Wide Smile Ltd | Health & social care | 2014 |
| Bigcam Ltd | Real estate | 2019 |
| Bigfish Investors Limited | Real estate | 2018 |
| Bigfoot Grooming Ltd | Wholesale & retail | 2025 |
| Bigth Limited | Information & communication | 2024 |
| Bikeability Wales | Arts & recreation | 2008 |
| Bill Will Waste Management Limited | Water & waste | 2015 |
| Billy Sharp Music Ltd | Information & communication | 2026 |
| BIN & LI International Trade Ltd | Wholesale & retail | 2024 |
| BIN Bags on Line Limited | Wholesale & retail | 2012 |
| BIN Hard (UK1) Limited | Wholesale & retail | 2018 |
| Binary Properties Cyfyngedig | Real estate | 2020 |
| Binoji's Kitchen Ltd | Hospitality | 2024 |
| Bio-Energy International Ltd | Water & waste | 2019 |
| Bio-Isolates Limited | Professional & scientific | 2016 |
| Biobased Solutions Ltd | Professional & scientific | 2011 |
| Biocontrol Innovation Centre Ltd | Professional & scientific | 2025 |
| Biomat Innovations Ltd | Professional & scientific | 2023 |
| Bionema Group Limited | Professional & scientific | 2012 |
| Biophilic Life Limited | Construction | 2021 |
| Biophillic Swansea Ltd | Agriculture & fishing | 2024 |
| Biosafety Systems Limited | Professional & scientific | 2024 |
| Biovici Limited | Administrative & support | 2013 |
| Bippa Development Limited | Real estate | 2013 |
| Bira Care Group Limited | Financial services | 2025 |
| Bira Care Homes Limited | Health & social care | 2014 |
| Bira Group Limited | Financial services | 2019 |
| Birb Vending Limited | Wholesale & retail | 2023 |
| Birch Fish Bar Limited | Hospitality | 2015 |
| Birch Socials Group Ltd | Professional & scientific | 2023 |
| Birch Tippers and Plant Limited | Transport & logistics | 2006 |
| Birchgrove Mini Travel Ltd | Transport & logistics | 2013 |
| Bird in Hand (Fforest) Limited | Hospitality | 2019 |
| Biresa Limited | Hospitality | 2002 |
| Birla Group Limited | Households | 2022 |
| Birwelco Limited | Professional & scientific | 2004 |
| Bishop Lifting Services (Wales) Limited | Wholesale & retail | 1982 |
| Bishop Road Limited | Real estate | 2025 |
| Bishop's Cafe Bistro Limited | Hospitality | 2018 |
| Bishops Stone Limited | Construction | 2025 |
| Bishopston Imaging Ltd | Health & social care | 2009 |
| Bislar Limited | Construction | 2025 |
| Bisp Civil Engineering Ltd | Construction | 2020 |
| BIT2BYTE Solutions Ltd | Wholesale & retail | 2024 |
| Bite Brazil Ltd | Hospitality | 2025 |
| Bits and Pieces (Clydach) Limited | Wholesale & retail | 2007 |
| Bitz & Pizzaz Ltd | Hospitality | 2015 |
| Bizee Software Limited | Information & communication | 2005 |
| Bizis Limited | Professional & scientific | 2005 |
| Bizzy Pubs Ltd | Hospitality | 2022 |
| BJ Holdings Ltd | Agriculture & fishing | 2010 |
| Bj's 2010 Limited | Extraterritorial | 2010 |
| Bjornen Consult Ltd | Professional & scientific | 2015 |
| BJT Maintenance Limited | Construction | 2019 |
| BKL Property Ltd | Real estate | 2020 |
| Black Belt Driver Ltd | Transport & logistics | 2025 |
| Black Belt Property Ltd | Real estate | 2023 |
| Black Cat PUB Company Limited | Hospitality | 2025 |
| Black EWE Limited | Hospitality | 2023 |
| Black Horse Cleaning Solutions Ltd | Administrative & support | 2025 |
| Black Iron Energy Ltd | Manufacturing | 2025 |
| Black LAB Films Ltd | Information & communication | 2017 |
| Black Lion Lampeter Ltd | Hospitality | 2019 |
| Black Lion United Limited | Hospitality | 2020 |
| Black Mountain Construction Services Limited | Construction | 2025 |
| Black Mountain Limited | Information & communication | 1981 |
| Black Mountain Mortgages Ltd | Financial services | 2025 |
| Black Mountain Products and Services Limited | Information & communication | 2013 |
| Black Mountain Properties Limited | Real estate | 1995 |
| Black Mountain Valley Ltd | Wholesale & retail | 2025 |
| Black TAR Brewing Co Ltd | Manufacturing | 2025 |
| Black Tread Limited | Wholesale & retail | 2018 |
| Black Welsh Music Awards CIC | Arts & recreation | 2025 |
| Black Welsh Music CIC | Information & communication | 2026 |
| Black Women Empowerment Network C.I.C. | Professional & scientific | 2024 |
| Blackbear Finance Limited | Financial services | 2025 |
| Blackbird Holdings Ltd | Professional & scientific | 2018 |
| Blackfoot Limited | Transport & logistics | 2000 |
| Blackham Properties Limited | Households | 2000 |
| Blackhills Caravan Sales Ltd | Wholesale & retail | 2007 |