| BIT Cargo Air & Sea Global Ltd | Transport & logistics | 2026 |
| Bitesize Therapy Limited | Real estate | 2017 |
| Bits and Boba Ltd | Wholesale & retail | 2022 |
| Bits and Parts Limited | Wholesale & retail | 2012 |
| BIZ Engineering Limited | Manufacturing | 1946 |
| BIZ Group Holdings Limited | Administrative & support | 2005 |
| BIZ Karts Limited | Manufacturing | 1987 |
| BIZ Pinnacle Limited | Wholesale & retail | 2023 |
| Bizbenefit Ltd | Professional & scientific | 2015 |
| Biznext Ltd | Professional & scientific | 2016 |
| Bizopti Ltd | Professional & scientific | 2015 |
| Bizzy Logistics Ltd | Transport & logistics | 2025 |
| Bizzy Trade Ltd | Wholesale & retail | 2020 |
| BJC (Billericay) Limited | Real estate | 2006 |
| Bkcuts Ltd | Other services | 2025 |
| Black and White RIO Ltd | Information & communication | 2025 |
| Black Birch Maintenance Ltd | Construction | 2021 |
| Black Birdcage Entertainment Ltd | Other services | 2014 |
| Black Cat Filmmaking Ltd | Arts & recreation | 2024 |
| Black Door Press Ltd | Information & communication | 2016 |
| Black FAN Close Management Limited | Real estate | 1988 |
| Black Legacy Limited | Wholesale & retail | 2023 |
| Black Tree Development Limited | Real estate | 2025 |
| Black Wall Street Media Ltd | Information & communication | 2023 |
| Blackarrow Ltd | Wholesale & retail | 2025 |
| Blackheath Fish & Chips Limited | Hospitality | 2021 |
| Blackline Estates Ltd | Real estate | 2025 |
| Blackness JA Ltd | Real estate | 2018 |
| Blacksmith Store Essex Ltd | Wholesale & retail | 2022 |
| Blackstone Hire Ltd | Administrative & support | 2025 |
| Blackstone Projects Ltd. | Construction | 2011 |
| Blackstripe Consultants Limited | Information & communication | 2010 |
| Blackwood Consultancy Ltd | Wholesale & retail | 2019 |
| Blacwater Brokers Ltd | Financial services | 2023 |
| Blacwater Consultancy Ltd | Professional & scientific | 2018 |
| Blade Bikelights Limited | Manufacturing | 2017 |
| Blanc River Ltd | Manufacturing | 2026 |
| Blaze Communication Limited | Professional & scientific | 1990 |
| Blefu Ltd | Hospitality | 2021 |
| Blended Learning Academy Ltd | Education | 2021 |
| Blfc & Ribs Limited | Hospitality | 2025 |
| Blinds Home Ltd | Wholesale & retail | 2022 |
| Blindsons Ltd | Hospitality | 2024 |
| Blink Surgident Ltd | Other services | 2023 |
| Bliss Roofing Contractors Ltd | Construction | 2017 |
| Blissful Needs Ltd | Wholesale & retail | 2024 |
| Blix Power Europe LP | | 2018 |
| Block 18-28 Crofton Way Management Company Limited | Households | 2002 |
| Block Investments Limited | Real estate | 2022 |
| BLOCK257 Ltd | Professional & scientific | 2026 |
| Blockage Busters Ltd | Water & waste | 2020 |
| Blood Sweat and Tea Marketing Limited | Professional & scientific | 2025 |
| Bloom and Roar Brand Consultancy Ltd | Professional & scientific | 2026 |
| Blooming Minds Centre for Counselling & Psychotherapy Ltd | Health & social care | 2022 |
| Blossom Lane Limited | Other services | 2016 |
| Blossomnation Limited | Transport & logistics | 2023 |
| BLP Plumbing Group Ltd | Construction | 2025 |
| Blue BG Limited | Construction | 2007 |
| Blue Cleaning Services Ltd | Administrative & support | 2024 |
| Blue Court Management Limited | Households | 2008 |
| Blue Donkey London Ltd | Administrative & support | 2019 |
| Blue Dragon Consultants Ltd | Professional & scientific | 2026 |
| Blue Holly Partnership Ltd | Real estate | 2016 |
| Blue INK Entertainment Ltd | Information & communication | 2025 |
| Blue Nails Limited | Other services | 2021 |
| Blue Oak Property Investment Limited | Real estate | 2025 |
| Blue Orchid Counselling and Consultancy Ltd | Health & social care | 2023 |
| Blue Star Transport Ltd | Transport & logistics | 2020 |
| Bluecircle IT Ltd | Information & communication | 2022 |
| Bluelight London Limited | Construction | 2021 |
| Blueline Security Limited | Public administration | 2017 |
| Blueprint of Zion Limited | Arts & recreation | 2018 |
| Bluequess Limited | Real estate | 2025 |
| Blustin Design Ltd | Professional & scientific | 2002 |
| BM Digital Marketing Ltd | Professional & scientific | 2018 |
| Bmagroup Ltd | Wholesale & retail | 2025 |
| BMB Property Maintenance Limited | Construction | 2025 |
| BMD Accountancy Ltd | Professional & scientific | 2023 |
| Bmgworknet Ltd | Construction | 2025 |
| BMH Tiles Ltd | Wholesale & retail | 2026 |
| BMS Corporate Limited | Administrative & support | 2009 |
| BMS Empresa Ltd | Real estate | 2021 |
| BMT Engineering Solutions Ltd | Construction | 2019 |
| Bmtc Properties Ltd | Real estate | 2019 |
| BN & Will Limited | Other services | 2021 |
| BNA Services Limited | Wholesale & retail | 2019 |
| BNA Tyres Ltd | Wholesale & retail | 2025 |
| BNP London Ltd | Construction | 2019 |
| BOB (Marketing) Limited | Professional & scientific | 2018 |
| Bobat Electrical Services Ltd | Professional & scientific | 2018 |
| Bobcreative Ltd | Arts & recreation | 2019 |
| Bodied by XO Ltd | Wholesale & retail | 2020 |
| Bodilabs Ltd | Arts & recreation | 2024 |
| Bodybymillie Ltd | Other services | 2024 |
| BODYBYXO2 Limited | Arts & recreation | 2021 |
| Bodyshop Support Limited | Professional & scientific | 2022 |
| Bohdidharma Perfume UK Limited | Wholesale & retail | 2017 |
| Boiler Surgeon Ltd | Construction | 2018 |
| Bold Industries Limited | Wholesale & retail | 2025 |
| Bombay Spice Takeaway (Enfield) Ltd | Hospitality | 2020 |