| Blaxmill (Twenty-Five) Limited | Professional & scientific | 2004 |
| Blaxmill (Twenty-Six) Limited | Professional & scientific | 2004 |
| Blay's Plumbing & Heating Ltd | Construction | 2012 |
| Blayds Mews Properties Limited | Households | 2019 |
| Blaymires Plumbing & Heating Limited | Construction | 2018 |
| Blaze Trap Innovations Ltd | Professional & scientific | 2026 |
| Blaze Trap Ltd | Professional & scientific | 2019 |
| Blazing Bites Ltd | Hospitality | 2025 |
| Bldg Workshop Ltd | Agriculture & fishing | 2018 |
| Blen Ltd | Extraterritorial | 2013 |
| Blend & Nourish Ltd | Hospitality | 2019 |
| Blend by G Limited | Other services | 2025 |
| BLEND8BLOOM Limited | Wholesale & retail | 2024 |
| Blenheim Advisory Limited | Professional & scientific | 2020 |
| Blenheim Financial Limited | Financial services | 2025 |
| Blenheim Tax Limited | Professional & scientific | 2025 |
| Blerim Ltd | Hospitality | 2022 |
| Bless Barbs Healthcare Limited | Health & social care | 2022 |
| Bless YOU Ltd | Wholesale & retail | 2017 |
| BLESS:44 Ltd | Wholesale & retail | 2020 |
| Blessington's Property Services Limited | Construction | 2025 |
| BLG (Burlington House) Limited | Real estate | 2018 |
| BLG Gordon Limited | Construction | 2014 |
| BLG Property Limited | Real estate | 2014 |
| BLG Space Properties Limited | Real estate | 2021 |
| Blhbc Ltd | Hospitality | 2025 |
| Blike Consult Ltd | Professional & scientific | 2024 |
| Bliksem Limited | Manufacturing | 2023 |
| Blind EYE Blink Limited | Real estate | 2016 |
| Blind Night Records Ltd | Information & communication | 2020 |
| Blind OWL Barbering Limited | Other services | 2017 |
| Blind Ventures Limited | Real estate | 2015 |
| Blindfaith Ventures Limited | Real estate | 2024 |
| Blinds & Co (Leeds) Ltd | Manufacturing | 2003 |
| Blinds 2 Suit Ltd | Wholesale & retail | 2017 |
| Blinds by Video Limited | Wholesale & retail | 2023 |
| Blinds for Apartments Ltd | Construction | 2023 |
| Blinds to YOU "2002" Limited | Manufacturing | 2002 |
| Blindsbypost Ltd | Wholesale & retail | 2018 |
| Blindsforlessyorkshire Ltd | Wholesale & retail | 2020 |
| Blindside Consulting Limited | Financial services | 2024 |
| Blink Studios Design Limited | Other services | 1998 |
| Blinkhorn Financial Limited | Administrative & support | 2006 |
| Blinok Limited | Hospitality | 2015 |
| Blinxy Lashes Ltd | Wholesale & retail | 2019 |
| Bliss (Killamarsh) Limited | Construction | 2019 |
| Bliss Bathrooms Limited | Construction | 2025 |
| Bliss Bites Catering Ltd | Hospitality | 2023 |
| Bliss Managing Ltd | Wholesale & retail | 2024 |
| Bliss Spa Limited | Other services | 2005 |
| Blissful GLO Cleaning Services Limited | Administrative & support | 2025 |
| Blissful Global Creations Ltd | Wholesale & retail | 2025 |
| Blissful Properties Global (UK) Ltd | Real estate | 2024 |
| Blissie Limited | Wholesale & retail | 2025 |
| Blite Ltd | Transport & logistics | 2025 |
| Blitz Brands Ltd | Wholesale & retail | 2024 |
| BLJ Hard Ding Property Limited | Real estate | 2024 |
| Blks Investments Ltd | Real estate | 2025 |
| Blnce Ltd | Wholesale & retail | 2026 |
| Bloc Properties Limited | Real estate | 2018 |
| Bloc Studio Wellness Limited | Arts & recreation | 2024 |
| Bloc Wellbeing CIC | Arts & recreation | 2021 |
| Blockchain IOT & Commerce Limited | Information & communication | 2016 |
| Blocpay Limited | Information & communication | 2020 |
| Blokes UP North Limited | Real estate | 1974 |
| Blood Sweat & Tears Enterprises Ltd | Arts & recreation | 2025 |
| Bloom Beauty Ltd | Other services | 2019 |
| Bloom Gardening Limited | Administrative & support | 2020 |
| Bloom Longevity Labs Ltd | Public administration | 2025 |
| Bloom NG Ltd | Administrative & support | 2026 |
| Bloom Skincare Clinic Ltd | Other services | 2023 |
| Bloomin Awesome Ltd | Other services | 2014 |
| Bloomin' Joy Ltd | Wholesale & retail | 2025 |
| Blooming Flora Limited | Administrative & support | 2020 |
| Blooming Life Limited | Health & social care | 2022 |
| Blooming Property Investments Limited | Real estate | 2016 |
| Bloomshill Ltd | Information & communication | 2023 |
| Bloomtree Ltd | Arts & recreation | 2020 |
| Blootek Ventures Capital Limited | Real estate | 2022 |
| Blootek Ventures Limited | Real estate | 2019 |
| Blootek Ventures Marketing Limited | Professional & scientific | 2025 |
| Blootek Ventures Trading Limited | Real estate | 2021 |
| Bloq Hoardings Ltd | Construction | 2025 |
| Blossom Care Services Ltd | Health & social care | 2025 |
| Blossom Childcare Consultancy Ltd | Professional & scientific | 2025 |
| Blossom Training Ltd | Professional & scientific | 2018 |
| Blossoming Property Ltd | Real estate | 2025 |
| Bloze Ltd | Wholesale & retail | 2015 |
| BLR (Flat Roofing) Ltd | Construction | 2025 |
| BLT Works Group Ltd | Construction | 2026 |
| BLU Boutique Ltd | Wholesale & retail | 2023 |
| BLU UK Holdings Limited | Financial services | 2023 |
| Blucentric Solutions Ltd | Wholesale & retail | 2024 |
| Blue and White Modelling Limited | Professional & scientific | 2025 |
| Blue Apple Holdings Limited | Professional & scientific | 2019 |
| Blue Apple Recruitment Limited | Professional & scientific | 2019 |
| Blue Apple Training Ltd | Education | 2012 |
| Blue Arrow Healthcare Ltd | Health & social care | 2020 |
| Blue Beech Limited | Other services | 2020 |
| Blue Box (UK) Limited | Extraterritorial | 2001 |