| Big MAN and Van Removals Ltd | Transport & logistics | 2019 |
| Big Pawrsonailty Limited | Wholesale & retail | 2025 |
| Big Red Button Limited | Information & communication | 2002 |
| Big Step Properties Limited | Real estate | 2024 |
| Big Trash Limited | Arts & recreation | 1984 |
| Bigdawgssrt Ltd | Administrative & support | 2024 |
| Bigsteps Consulting Ltd | Other services | 2011 |
| Bilal Supermarket Ltd | Wholesale & retail | 2016 |
| Bimavens Limited | Information & communication | 2026 |
| BIN N Gone Limited | Water & waste | 2012 |
| Binderella Limited | Information & communication | 2017 |
| Bindi Holdings Limited | Financial services | 2020 |
| Bindi Investments Limited | Real estate | 2019 |
| Biodanza UK Limited | Arts & recreation | 1998 |
| Birchanger Investment Company Limited | Real estate | 1962 |
| Birchworth Limited | Real estate | 2007 |
| Bird Events Ltd | Other services | 2020 |
| BIS Coatings (UK) Limited | Construction | 2021 |
| Bishendas Brothers Limited | Real estate | 2014 |
| Bishopken Limited | Real estate | 2016 |
| Bisons International Limited | Wholesale & retail | 2019 |
| Bisou Clinics Limited | Health & social care | 2017 |
| Bite Runners Ltd | Hospitality | 2025 |
| Bizi Holdings Limited | Professional & scientific | 2006 |
| Bizware Solutions Ltd | Information & communication | 2017 |
| Bjes Limited | Construction | 2013 |
| BJP Investments Limited | Real estate | 2020 |
| BJP Law Limited | Professional & scientific | 2022 |
| Bkbooks Limited | Wholesale & retail | 2026 |
| BKS Surveyors Ltd | Professional & scientific | 2023 |
| Bkynd Limited | Administrative & support | 2020 |
| Blachill Limited | Information & communication | 2005 |
| Black Girls Brunch UK C.I.C. | Hospitality | 2020 |
| Black Oak Investment Group Limited | Financial services | 2020 |
| Blackberry Properties Limited | Construction | 2014 |
| Blackfriars Investments (Management) Limited | Real estate | 1995 |
| Blackfriars Investments Limited | Professional & scientific | 1995 |
| Blackfriars Land Company Limited | Administrative & support | 1997 |
| Blackpearl Finance Ltd | Financial services | 2025 |
| Blackridge Investments Limited | Real estate | 2016 |
| Blackrush Ltd | Information & communication | 2020 |
| Bladon Sears (Properties) Limited | Construction | 2004 |
| Bladon Sears Limited | Real estate | 2002 |
| Blakescdesigns Ltd | Wholesale & retail | 2024 |
| Blam Ltd | Wholesale & retail | 2005 |
| Blankson Sodha Associates Ltd | Wholesale & retail | 2010 |
| Blase Productions Limited | Other services | 2018 |
| BLB General Construction Limited | Construction | 2025 |
| Blend Ventures Ltd | Professional & scientific | 2016 |
| Blenheim Estates Limited | Real estate | 1997 |
| Blenheim Leicester Limited | Real estate | 2024 |
| Blenheim Nursing Homes Limited | Real estate | 2005 |
| Blenheim Property Management Limited | Real estate | 1997 |
| Blert Properties Ltd | Real estate | 2016 |
| Blimp Media Limited | Professional & scientific | 2019 |
| Blingstone UK Limited | Professional & scientific | 2023 |
| Blio Ltd | Information & communication | 2021 |
| Blisique Limited | Manufacturing | 2017 |
| Bliss Station Ltd | Information & communication | 2021 |
| Blitzfair Limited | Construction | 1985 |
| BLM Author Limited | Extraterritorial | 2012 |
| Block 401 Limited | Real estate | 2025 |
| Blocknet Consulting Ltd | Information & communication | 2019 |
| Bloom Legal Recruitment Limited | Administrative & support | 2012 |
| Bloom Therapeutic Services Limited | Health & social care | 2025 |
| Blossom Beauty Academy Limited | Education | 2018 |
| BLT Group Ltd | Wholesale & retail | 2026 |
| BLU Design Limited | Information & communication | 2011 |
| BLU Jewellery Limited | Manufacturing | 2025 |
| Blubear Ltd | Wholesale & retail | 2019 |
| Blue 9 Security Limited | Public administration | 2006 |
| Blue Banana Distributors Ltd | Wholesale & retail | 2011 |
| Blue Diamond Security Solutions Limited | Administrative & support | 2007 |
| Blue Four Associates Ltd | Professional & scientific | 2004 |
| Blue Horse Design Limited | Other services | 2015 |
| Blue Meadow Solutions Ltd | Information & communication | 2012 |
| Blue Moon Academy Ltd | Education | 2024 |
| Blue Peak Investments Ltd | Real estate | 2024 |
| Blue Song Consulting Ltd | Financial services | 2025 |
| Blue Steed Consultancy Limited | Professional & scientific | 2003 |
| Blue Winder Ltd | Professional & scientific | 2025 |
| Bluebelle Ventures Limited | Construction | 2022 |
| Bluebridge Asset Management Ltd | Administrative & support | 2025 |
| Bluebridge Group Limited | Administrative & support | 2025 |
| Bluepoint Brivio Limited | Real estate | 2025 |
| Blueprints Collective Ltd | Arts & recreation | 2015 |
| Bluesprite Limited | Information & communication | 2012 |
| Blunt London Limited | Professional & scientific | 2011 |
| Bluorca Plumbing & Heating Ltd | Construction | 2025 |
| Blythe House Estates Limited | Real estate | 2006 |
| BMC Financial Planning Ltd | Financial services | 2017 |
| BMP Holdco Ltd | Financial services | 2025 |
| BMS Chesham Ltd | Construction | 2019 |
| BNO Marketing Limited | Professional & scientific | 2023 |
| BO88 Ltd | Information & communication | 2023 |
| Board Game Accessories Limited | Wholesale & retail | 2025 |
| Board Measures Limited | Professional & scientific | 2026 |
| Boca Drylining Ltd | Construction | 2024 |
| Body Matters Skin Ltd | Other services | 2025 |
| Body Matters Spa Ltd | Other services | 2025 |