| Bj&P Services Limited | Information & communication | 2009 |
| Bjgan Ltd | Wholesale & retail | 2025 |
| BJM IG Privacy Limited | Information & communication | 2018 |
| BJV Tech Ltd | Wholesale & retail | 2025 |
| BL Carpentry & Construction Ltd | Construction | 2025 |
| Black & White Property Management Ltd | Households | 2019 |
| Black Badges Ltd | Wholesale & retail | 2017 |
| Black BUN Limited | Other services | 2020 |
| Black Cedar and Teakwood Limited | Real estate | 2021 |
| Black Diamond Services Consultancy Ltd | Professional & scientific | 2022 |
| Black Iris Flowers Ltd | Wholesale & retail | 2024 |
| Black Knight Labs Ltd | Information & communication | 2023 |
| Black Pearl Interactive Limited | Professional & scientific | 2008 |
| Black River (Technical Services) Limited | Agriculture & fishing | 1995 |
| Black Seed Carry Vehicle LLP | | 2022 |
| Black Seed GP LLP | | 2022 |
| Black Seed LP | | 2022 |
| Black Star Construction Ltd | Construction | 2026 |
| Black Taxi Hearse Hire Ltd | Other services | 2023 |
| Black Trans Foundation C.I.C. | Health & social care | 2021 |
| Black Watermelon Ltd | Hospitality | 2021 |
| Blackbridge Capital Ltd | Financial services | 2023 |
| Blacks of Sopwell Limited | Manufacturing | 2005 |
| Blackshield International Ltd | Information & communication | 2025 |
| Blackwater Accountants & Tax Advisers Limited | Professional & scientific | 2020 |
| Blade Logistics Ltd | Transport & logistics | 2011 |
| Blagoy Yanchev Limited | Manufacturing | 2008 |
| Blake Luxury Mini Coach Travel Ltd | Transport & logistics | 2003 |
| Blanaru Ltd | Construction | 2024 |
| Blankpad Ltd | Real estate | 2023 |
| Blaxills Fitted Furniture Limited | Construction | 2015 |
| BLC Construction Solutions Ltd | Construction | 2025 |
| BLC Maintenance Limited | Real estate | 2015 |
| Bletchley Industries Limited | Financial services | 2025 |
| Blink Charging Holdings UK Limited | Financial services | 2015 |
| Blink Charging UK Limited | Administrative & support | 2015 |
| Blink Consulting & Tech Ltd | Professional & scientific | 2018 |
| Blissful Being Ltd | Wholesale & retail | 2020 |
| Blizzard Plastering Ltd | Construction | 2024 |
| Block 4 Phoenix Park Property Management Company Ltd | Households | 2024 |
| Block Fire Ltd | Construction | 2026 |
| Blood Red Ventures Ltd | Hospitality | 2016 |
| Bloom Clinical Ltd | Health & social care | 2024 |
| Bloom Enterprise Limited | Financial services | 2019 |
| Bloom Teas Limited | Manufacturing | 2010 |
| Bloomsbury Commercial Property Surveyors Ltd | Administrative & support | 2020 |
| Bloomsbury Construction Ltd | Construction | 2020 |
| Bloomsbury Court (ST Albans) Management Company Limited | Households | 2016 |
| Bloomsbury Homes Limited | Construction | 2003 |
| Blue Allium HR Ltd | Professional & scientific | 2016 |
| Blue Cat Design Ltd | Manufacturing | 2015 |
| Blue Chyp Limited | Manufacturing | 2009 |
| Blue Consultant Services Ltd | Professional & scientific | 2025 |
| Blue Curve Solutions Ltd | Information & communication | 2019 |
| Blue Green Ocean Limited | Construction | 2017 |
| Blue Jewels Ltd | Hospitality | 2026 |
| Blue Light Workforce Solutions Ltd | Administrative & support | 2024 |
| Blue Orchard Estates Ltd | Real estate | 2022 |
| Blue Paradise Properties Ltd | Real estate | 2018 |
| Blue Riband Reporting Limited | Health & social care | 2015 |
| Blue Rose Consultancy Limited | Real estate | 2017 |
| Blue Spherical Limited | Information & communication | 2022 |
| Bluebell Residents Association Limited | Households | 2009 |
| Bluebells Taxi Ltd | Transport & logistics | 2025 |
| Bluebird Properties & Lettings Ltd | Real estate | 2024 |
| Bluecroft Consultants Limited | Administrative & support | 2022 |
| Bluefern Designs Limited | Professional & scientific | 2025 |
| Bluefin Land Limited | Real estate | 2018 |
| Bluelight Lifetime Partners Limited | Financial services | 2013 |
| Blueseed Learning Solutions Limited | Information & communication | 2004 |
| Bluesquare and Associates Ltd | Financial services | 2022 |
| Bluetouchpaper Consulting Limited | Professional & scientific | 2014 |
| Blutok Limited | Information & communication | 2010 |
| Blyth Developments Limited | Extraterritorial | 2007 |
| BMON25 Investment Limited | Real estate | 2025 |
| BMP General Construction Ltd | Construction | 2024 |
| Bnpharma Ltd | Professional & scientific | 2021 |
| Boadicea Technologies Limited | Real estate | 2012 |
| BOB Jones and Daughters Ltd | Agriculture & fishing | 2014 |
| Bodkin Lane Limited | Arts & recreation | 2008 |
| Body Tempering Limited | Arts & recreation | 2020 |
| Body Tempering UK Limited | Arts & recreation | 2020 |
| Bodylimit Gym Limited | Arts & recreation | 2016 |
| Bodyrevolution Training Limited | Arts & recreation | 2023 |
| Boffin Life Ltd | Financial services | 2023 |
| Boffin Media Limited | Professional & scientific | 2014 |
| Boghani Consultancy Services Ltd | Information & communication | 2012 |
| Boinclo Ltd. | Wholesale & retail | 2016 |
| Bolero Queens World Music Limited | Arts & recreation | 2021 |
| Bolt Building & Maintenance Ltd | Construction | 2014 |
| Bond Street (CS) Limited | Real estate | 2019 |
| Bonsai HR Ltd | Administrative & support | 2025 |
| Boodhun Medical Services Ltd | Health & social care | 2023 |
| Bookdmedia Ltd | Information & communication | 2026 |
| Bookkeeping Made Easy Services Limited | Professional & scientific | 2013 |
| Books on the Hill Ltd | Professional & scientific | 2015 |
| Boolean Logic Limited | Information & communication | 2009 |
| Booth Glazing Limited | Construction | 2026 |
| Bootproof Ltd | Manufacturing | 2024 |
| Booze on Wheels Limited | Hospitality | 2017 |