| Blacksmith Homes Ltd | Construction | 2024 |
| Blacktree Technologies Limited | Administrative & support | 2012 |
| Blade Ecology Ltd | Professional & scientific | 2020 |
| Blade Landscape Architects Ltd | Professional & scientific | 2017 |
| Blade Trees Ltd | Professional & scientific | 2021 |
| Blaggit Limited | Information & communication | 2024 |
| Blake & Co Property Limited | Real estate | 2026 |
| Blake Accountancy Limited | Professional & scientific | 2019 |
| Blakebrook Ltd | Professional & scientific | 1991 |
| Blakeman's Contracting Ltd | Professional & scientific | 2022 |
| Blaze Technologies Limited | Information & communication | 2026 |
| BLC Cleaning Ltd | Administrative & support | 2022 |
| Bldn Clothing Limited | Wholesale & retail | 2017 |
| Blindsforyou Ltd | Construction | 2020 |
| Blisjay Travels & Tours Ltd | Wholesale & retail | 2024 |
| Bliss Mill Management Limited | Households | 1993 |
| Blitbolt Limited | Construction | 2013 |
| Bloatify Ltd | Information & communication | 2025 |
| Bloomfield Wealth Management Ltd | Financial services | 2014 |
| Blooming Imaginations Ltd | Education | 2019 |
| Blossom Tree Dog Supplies Ltd | Wholesale & retail | 2022 |
| BLT Logistics Limited | Agriculture & fishing | 2018 |
| Blubuilt Ltd | Construction | 2018 |
| Blue and Co. EOT Limited | Extraterritorial | 2022 |
| Blue and Co. Limited | Construction | 1993 |
| Blue Box Software Limited | Information & communication | 2005 |
| Blue Diamond Vapors UK Limited | Wholesale & retail | 2015 |
| Blue Fire Communications Limited | Extraterritorial | 2009 |
| Blue Flame Ember Ltd | Wholesale & retail | 2025 |
| Blue Marble Asset Management Limited | Real estate | 2010 |
| Blue Marble Events Ltd | Arts & recreation | 2025 |
| Blue Marble Properties Limited | Extraterritorial | 2015 |
| Blue Martini Ltd | Transport & logistics | 2020 |
| Blue Monarch Business Services Ltd | Administrative & support | 2023 |
| Blue Mountain Refreshments Ltd | Wholesale & retail | 2020 |
| Blue Opal Limited | Health & social care | 2006 |
| Blue Route Express Ltd | Transport & logistics | 2025 |
| Blue Sea Holidays Limited | Administrative & support | 2007 |
| Blue Squared Solutions Limited | Information & communication | 2024 |
| Blue Squirrel Software Ltd | Information & communication | 2009 |
| Blue Task Limited | Construction | 1998 |
| BLUE22 Ltd | Hospitality | 2025 |
| Bluebell Retreat Limited | Hospitality | 2014 |
| Bluebirch Services UK Ltd | Professional & scientific | 2018 |
| Bluecube UV Tech (UK) Ltd | Administrative & support | 2021 |
| Blueeve Limited | Transport & logistics | 2026 |
| Bluehendrix Limited | Information & communication | 2014 |
| Bluemark Developments Limited | Construction | 2005 |
| Blueprint Training Limited | Arts & recreation | 2015 |
| Bluewave IT Solutions Ltd | Wholesale & retail | 2024 |
| Bluewave Mortgages and Protection Ltd | Financial services | 2022 |
| Bluline Administration Limited | Other services | 2017 |
| Bluline Gloucestershire Limited | Other services | 2013 |
| Bluline Health Limited | Other services | 2013 |
| Bluline West Yorkshire Limited | Health & social care | 2014 |
| Bluseal (Holdings) Limited | Financial services | 2010 |
| Bluseal Doors Limited | Extraterritorial | 2010 |
| Bluseal Limited | Manufacturing | 2004 |
| Bluseal Metals Limited | Extraterritorial | 2010 |
| Bmmc Limited | Construction | 2021 |
| Bmsquare Ltd | Health & social care | 2025 |
| Boar Valley Investments Limited | Real estate | 2023 |
| Boathouse Events and Management Limited | Hospitality | 2022 |
| Bobble Maintenance Services Limited | Construction | 2017 |
| Bobbysahota.Com Ltd | Professional & scientific | 2024 |
| Bodable Ltd | Wholesale & retail | 2026 |
| Body Shop Accident Repair Centre (Melksham) Ltd | Wholesale & retail | 2012 |
| Bohe Ltd | Extraterritorial | 2003 |
| Boho Ltd | Real estate | 2003 |
| Bohoism Ltd | Other services | 2005 |
| Boiler Choice Limited | Wholesale & retail | 2019 |
| Boism Ltd | Extraterritorial | 2005 |
| Bolero Enterprises Limited | Hospitality | 2008 |
| Bombonera Limited | Wholesale & retail | 2016 |
| Bone & Co LLP | | 2009 |
| Bonehill Construction and Contracting Services Ltd | Construction | 2023 |
| Bonitas Group Holdings Limited | Financial services | 2020 |
| Bonnard Group Ltd | Administrative & support | 2023 |
| Bonterre CIC | Agriculture & fishing | 2014 |
| BOO! Solutions Limited | Construction | 2010 |
| Book-O-Tel Limited | Administrative & support | 1995 |
| Bookkeeping and Accountancy Direct Ltd | Administrative & support | 2013 |
| Bookotel Events LLP | | 2009 |
| Boolean Operating Systems Ltd | Information & communication | 2026 |
| Boom Motors Ltd | Wholesale & retail | 2026 |
| Boombox Golf Limited | Arts & recreation | 2024 |
| Boomtown Bangers Limited | Hospitality | 2023 |
| Boost Personnel Limited | Administrative & support | 2024 |
| Bootforce Limited | Construction | 2015 |
| Borba Tattoo Limited | Arts & recreation | 2026 |
| Boreas Holdings Limited | Financial services | 2017 |
| Born Media Productions Ltd | Information & communication | 2023 |
| Borrowed Brains Group Ltd | Professional & scientific | 2025 |
| Borwell Limited | Information & communication | 2003 |
| Boscawen Street Limited | Financial services | 2020 |
| Bosch Thermotechnology Ltd | Manufacturing | 1986 |
| Boss Industrial Group Limited | Administrative & support | 2005 |
| Boston Fast Food Ltd | Hospitality | 2025 |
| Boston Matthews Limited | Manufacturing | 1986 |
| Boston Matthews Machinery Limited | Manufacturing | 1984 |