| Biome Limited | Manufacturing | 2003 |
| Bionovogene Limited | Professional & scientific | 2026 |
| Black COD Solutions Ltd | Professional & scientific | 2022 |
| Black Diamond Brokers Ltd | Financial services | 2020 |
| Black Diamond Investment Bank Ltd | Administrative & support | 2009 |
| Black Door Yachting Ltd | Arts & recreation | 2021 |
| Black House Farm Management Company Limited | Professional & scientific | 2006 |
| Black Stork Investments LLP | | 2021 |
| Black Swan Business SET UP Services Ltd | Professional & scientific | 2024 |
| Blackfort Ltd | Administrative & support | 2021 |
| Blackheath Care Limited | Health & social care | 2016 |
| Blackwater Capital International Ltd | Financial services | 2021 |
| Blades Barber Lounge Ltd | Other services | 2026 |
| Blavo & Co. Solicitors Limited | Professional & scientific | 2011 |
| Blenheim Software International Limited | Information & communication | 1996 |
| Bleu Blanc Ocean Racing Ltd | Arts & recreation | 2016 |
| Blocktimum Digital Assets PLC | Financial services | 2015 |
| Blocktimum Investments Ltd | Financial services | 2018 |
| Bloem Real Estate Ltd | Real estate | 2024 |
| Blooming Bliss Ltd | Real estate | 2025 |
| BLR Capital Investments Ltd | Real estate | 2023 |
| Blue Renova Ltd | Construction | 2025 |
| Blue Rondo Ltd | Real estate | 2025 |
| Blue Rose Care Limited | Health & social care | 2013 |
| Blue Skye Homes Ltd | Real estate | 2019 |
| Bluebell Real Estate Ltd | Real estate | 2025 |
| Blueberry Publishing Ltd | Information & communication | 1997 |
| Blueberry Research Limited | Administrative & support | 2008 |
| Bluebutterfly Property Ltd | Real estate | 2023 |
| Bluefields Energy Limited | Professional & scientific | 2017 |
| Bluefields Energy Marketing Limited | Wholesale & retail | 2017 |
| Bluefields Management Limited | Professional & scientific | 2015 |
| Bluelight Employment Limited | Health & social care | 2015 |
| Blueorka Construction Limited | Construction | 2022 |
| Blueorka Limited | Construction | 2020 |
| Bluerock Contracting Limited | Water & waste | 2025 |
| Bluesoul Global Ltd | Other services | 2024 |
| BMH Building Solutions Limited | Construction | 2021 |
| Bocaddon Limited | Information & communication | 2020 |
| Bodyscanner Support International Limited | Administrative & support | 2024 |
| Bogaers Properties Ltd | Real estate | 2025 |
| Bold Endeavours Group Ltd | Information & communication | 2008 |
| Bond Street Property Ltd | Real estate | 2022 |
| Boond Ltd | Wholesale & retail | 2023 |
| Bootea Limited | Wholesale & retail | 2012 |
| BOS Holdings Limited | Real estate | 2022 |
| BOS Properties Ltd | Real estate | 2020 |
| Bossdale Ltd | Real estate | 2022 |
| Boston Buildings Cardiff Ltd | Construction | 2024 |
| Bottega Productions Limited | Professional & scientific | 2025 |
| Boundless AI Limited | Information & communication | 2025 |
| Bourneside Group Limited | Wholesale & retail | 2023 |
| Bowmann Associates Limited | Construction | 2017 |
| Box Bear Pictures Limited | Information & communication | 2015 |
| Braakman Real Estate Investment Ltd | Real estate | 2024 |
| Bradway Care Home Holdings Limited | Financial services | 2019 |
| Bradway Care Home Limited | Construction | 2015 |
| Bradway Care Limited | Health & social care | 2019 |
| Brained Impact Ltd | Professional & scientific | 2022 |
| Bramfield Securities Limited | | 1973 |
| Brand Brilliance Ltd | Information & communication | 2023 |
| Brands Property Ltd | Real estate | 2023 |
| Brannon Ltd | Professional & scientific | 2024 |
| Brasserie 191 Ltd | Professional & scientific | 2014 |
| Brazzacott Paint & Body Limited | Wholesale & retail | 2016 |
| Brewers Build Limited | Construction | 2024 |
| Brewpack Limited | Manufacturing | 1995 |
| Brick & Beam Properties Ltd | Manufacturing | 2018 |
| BRICK4YOU Ltd | Real estate | 2021 |
| Bricks & Passion Ltd | Real estate | 2021 |
| Brickwise Capital Ltd | Real estate | 2025 |
| Bridge House of Twyford Ltd | Health & social care | 2012 |
| Bright Futures Rentals Ltd | Hospitality | 2025 |
| Bright Personnel Limited | Administrative & support | 2006 |
| Brightgrove Limited | Other services | 2007 |
| Brightside Real Estate Ltd | Real estate | 2021 |
| Brikstone Ltd | Professional & scientific | 2022 |
| Bring Your 'a' Game Consulting Ltd | Professional & scientific | 2014 |
| Brisby Properties LLP | | 2005 |
| Britannica Accounting Ltd | Professional & scientific | 2000 |
| Britannica Consulting Ltd | Transport & logistics | 2015 |
| Britannica Corporation LLP | | 2023 |
| Britannica Investments Ltd | Professional & scientific | 1990 |
| Britasia Home Improvment Ltd | Construction | 2021 |
| Brizzi Investments UK Ltd | Real estate | 2025 |
| Broak Limited | Real estate | 2021 |
| Broek Properties Ltd | Real estate | 2020 |
| Brook & Smid Property Ltd | Real estate | 2025 |
| Brooklands Staff Bureau Limited | Administrative & support | 1978 |
| Bros and Co Consulting Ltd | Information & communication | 2026 |
| Bros and Co Group Ltd | Professional & scientific | 2020 |
| Bros and Co Holdings Ltd | Financial services | 2025 |
| Brownacre Capital Limited | Construction | 2017 |
| Brunel Precision Engineering Limited | Professional & scientific | 2022 |
| Brunetres Properties Ltd | Real estate | 2026 |
| Brunner Properties Ltd | Real estate | 2022 |
| Bscfm Property Invest Ltd | Real estate | 2022 |
| BSM Prop Limited | Real estate | 2018 |
| Bucks DIE Casting Company Limited(The) | Manufacturing | 1941 |
| Bugday Global Ltd | Professional & scientific | 2025 |