| Blackhills Community Supported Agriculture CIC | Agriculture & fishing | 2023 |
| Blackhills Leisure (Gower) Limited | Hospitality | 1978 |
| Blackpill Associates Ltd | Professional & scientific | 2023 |
| Blackpill Property Ltd | Real estate | 2024 |
| Blackridge Engineering Limited | Professional & scientific | 2025 |
| Blackrock Living Ltd | Real estate | 2020 |
| Blacksea Cafe Ltd | Hospitality | 2025 |
| Blackseed Property Ltd | Real estate | 2024 |
| Bladdercare Limited | Health & social care | 2019 |
| Blaen Y Gors Farm Ltd | Agriculture & fishing | 2026 |
| Blaen-Y-Maes Drop in Centre CIC | Other services | 2024 |
| Blaenymaes Stores Ltd | Wholesale & retail | 2020 |
| Blake Commercial Properties Limited | Real estate | 2024 |
| Blake’S Party Hire Ltd | Administrative & support | 2025 |
| Blank Group Ltd | Administrative & support | 2016 |
| Blastd Ltd | Wholesale & retail | 2022 |
| BLB Business Advisors Limited | Professional & scientific | 2022 |
| Blba Limited | Wholesale & retail | 2020 |
| Bledi Hand Car Wash Ltd | Wholesale & retail | 2018 |
| Blessed Island UK Ltd | Wholesale & retail | 2022 |
| Blinds Express Limited | Manufacturing | 2009 |
| Blinging Stunning Ltd | Wholesale & retail | 2019 |
| Blinkin-Bananas Limited | Wholesale & retail | 2010 |
| Bliss Apartments Limited | Real estate | 2008 |
| Bliss Bedding Limited | Manufacturing | 2007 |
| Bliss Cleaning Group Ltd | Administrative & support | 2022 |
| Blitzer Group Ltd | Administrative & support | 2024 |
| BLJ Travel Ltd | Administrative & support | 2023 |
| Bllr Properties Limited | Real estate | 2008 |
| Block 3 Vivian Mansions Management Company Limited | Households | 1986 |
| Block a Gelli Rhedyn RTM Company Limited | Real estate | 2020 |
| Block B Gelli Rhedyn RTM Company Limited | Real estate | 2020 |
| Block Property Maintenance Limited | Construction | 2024 |
| Bloke Barber Limited | Other services | 2021 |
| Bloom Lounge Cafe Ltd | Hospitality | 2025 |
| Bloomer Accountancy Limited | Professional & scientific | 2014 |
| Blooming Belles Limited | Other services | 2023 |
| Bloomnow Limited | Wholesale & retail | 2024 |
| Bloomsbury Economics Ltd | Professional & scientific | 2016 |
| Bloorcorp Ltd | Information & communication | 2015 |
| Blotch Ltd | Professional & scientific | 2025 |
| Blount Properties Limited | Real estate | 2018 |
| BLU Asset Holdings Ltd | Administrative & support | 2026 |
| BLU Thomas Ltd | Manufacturing | 2015 |
| BLU Thomas Medical Ltd | Manufacturing | 2019 |
| Blue Alpha Management Consultants Limited | Information & communication | 2004 |
| Blue Bubbles Services Ltd | Administrative & support | 2025 |
| Blue Butterfly Properties Ltd | Real estate | 2025 |
| Blue Chip Innovation Ltd | Professional & scientific | 2015 |
| Blue Cornflower Limited | Professional & scientific | 2024 |
| Blue Crystal Azure Limited | Administrative & support | 2016 |
| Blue Electronics Design Solutions Limited | Information & communication | 2009 |
| Blue Fairy Bridal Limited | Wholesale & retail | 2005 |
| Blue Land Consultancy Limited | Professional & scientific | 2006 |
| Blue Nile Centre Ltd | Wholesale & retail | 2025 |
| Blue Palm Apartments Ltd | Hospitality | 2019 |
| Blue Press Media Ltd | Professional & scientific | 2025 |
| Blue Rock Capital A4 Ltd | Real estate | 2025 |
| Blue Rock Construction Limited | Construction | 2006 |
| Blue Rock Demolition Ltd | Construction | 2019 |
| Blue Sky Grill Limited | Hospitality | 2020 |
| Blue Sky Holding Group Ltd | Real estate | 2025 |
| Blue Sky Laser Technologies Ltd | Manufacturing | 2016 |
| Blue Sky Metal Fabrication Ltd | Manufacturing | 2019 |
| Blue Water Bottle Ltd | Wholesale & retail | 2021 |
| Bluebell Gwesty Limited | Hospitality | 2022 |
| Bluebell Property Holdings Limited | Professional & scientific | 2016 |
| Bluebell Specialist Support Limited | Administrative & support | 2014 |
| Bluebell Wood Pet Crematorium Limited | Other services | 2023 |
| Bluebox Optics Limited | Manufacturing | 2017 |
| Bluemoon Healthcare Limited | Health & social care | 2016 |
| Bluephoenix AI Ltd | Administrative & support | 2023 |
| Blueprint Financial Holdings Limited | Financial services | 2020 |
| Bluestaff Property Ltd. | Real estate | 2026 |
| Bluetree Installations Ltd | Construction | 2014 |
| Blush and Feather Limited | Other services | 2024 |
| Blytt Ltd | Construction | 2013 |
| BLZ Trading Ltd | Information & communication | 2025 |
| BM Carpentry Solutions Limited | Construction | 2026 |
| Bmech Limited | Construction | 2018 |
| BMJ & RS Properties Ltd | Real estate | 2022 |
| BML Interiors Limited | Construction | 2025 |
| BML Property and Maintenance Ltd | Real estate | 2024 |
| BML Property Showcase Ltd | Real estate | 2022 |
| BMR Decoration Services Ltd | Construction | 2025 |
| BMS Property Investing Ltd | Real estate | 2024 |
| BNA Vehicles Ltd | Wholesale & retail | 2025 |
| Boapio Ltd | Information & communication | 2011 |
| Bobby Cole Music Ltd | Information & communication | 2016 |
| Bodhi White Properties Ltd | Real estate | 2025 |
| Bodlon Limited | Real estate | 2005 |
| Body Mind Soul Osteopathy Ltd | Health & social care | 2021 |
| Body Project Systems Ltd | Arts & recreation | 2013 |
| Body Reform PT Limited | Health & social care | 2011 |
| Bodyfreaks Limited | Wholesale & retail | 2016 |
| Bodyfreakz Activewear Ltd | Wholesale & retail | 2026 |
| Bodyshop Repair Network Limited | Wholesale & retail | 2008 |
| Boeen Ltd | Wholesale & retail | 2025 |
| Bohan Limited | Professional & scientific | 2013 |
| Bohgan Ltd | Wholesale & retail | 2017 |