| Blackwater Fencing Ltd | Administrative & support | 2025 |
| Blackwater GRC Ltd | Professional & scientific | 2025 |
| Blackwater Osteopathic Clinic Ltd | Professional & scientific | 2015 |
| Blackwater Pharma Ltd | Health & social care | 2008 |
| Blackwater Podiatry Ltd | Health & social care | 2025 |
| Blackwater Professional Services Ltd | Professional & scientific | 2026 |
| Blackwater Rubber and Plastic Extrusions Limited | | 1978 |
| Blackwater Sailing Club Limited | Arts & recreation | 1960 |
| Blackwater Scaffolding Limited | Other services | 2000 |
| Blastit Limited | Construction | 1992 |
| Blinds N' Blessings Ltd | Manufacturing | 2006 |
| Bling Bling Nails 999 Ltd | Other services | 2024 |
| Bliss Bridgwater Ltd | Hospitality | 2024 |
| Block G Freeholders Limited | Households | 1999 |
| Bloomfield Finance Limited | Financial services | 2024 |
| Bloomsbury Property Finance Limited | Financial services | 2008 |
| Blount Shutters Limited | Manufacturing | 1984 |
| BLP Group Ltd | Financial services | 2014 |
| Blue Block Limited | Transport & logistics | 2025 |
| Blue Cactus Digital Ltd | Professional & scientific | 2017 |
| Blue Cube Consulting Ltd | Information & communication | 2022 |
| BLUE2 Contractors Ltd | Construction | 2018 |
| Bluepencil Designs Ltd | Professional & scientific | 2012 |
| Blues Clothing Limited | Wholesale & retail | 1987 |
| Blues Group (Holdings) Limited | Manufacturing | 2013 |
| Blues Group Ltd | Wholesale & retail | 2017 |
| Blues Nightwear Limited | Wholesale & retail | 2015 |
| BNG Works Limited | Agriculture & fishing | 2023 |
| BOD Marine Limited | Manufacturing | 2024 |
| Bodi Barbers Ltd | Other services | 2019 |
| Bodxan Co Ltd | Financial services | 2021 |
| Bold-Sp (UK) Ltd | Extraterritorial | 2025 |
| Bollfilter U.K. Limited | Wholesale & retail | 1999 |
| Bond Legacy Property Group Limited | Financial services | 2025 |
| BOO Theatre and Entertainment Ltd | Education | 2025 |
| Bookbridge Forwarders Limited | Professional & scientific | 1994 |
| Booker HR Consulting Limited | Health & social care | 2017 |
| Borough Bejou Limited | Wholesale & retail | 2021 |
| Borough Carpets Ltd | Wholesale & retail | 2016 |
| Boswells Residential Limited | Real estate | 2014 |
| Boucherne Ltd | Health & social care | 2002 |
| Boudicca Financial Solutions Ltd | Financial services | 2012 |
| Boujee Nails & Beauty Limited | Other services | 2017 |
| Bourners Limited | Construction | 2017 |
| Bowman Bespoke Limited | Manufacturing | 2020 |
| Box Consolidators Limited | Extraterritorial | 1978 |
| BOX2BURN Limited | Arts & recreation | 2024 |
| BP Group Limited | Financial services | 2017 |
| BP Health & Safety Consultants Limited | Professional & scientific | 2012 |
| Bradwell Bay Ltd. | Transport & logistics | 2013 |
| Branch Hotel Limited | Hospitality | 2009 |
| Brandpointe Limited | Professional & scientific | 2009 |
| Braxted Interiors Limited | Professional & scientific | 2013 |
| Bray Giffin Accountants Limited | Professional & scientific | 2021 |
| Bray House Management Limited | Households | 1996 |
| Breakspear Share Redistribution Ltd | Financial services | 2023 |
| Breakspear Ventures Ltd | Financial services | 2021 |
| Brecrest Fashion Limited | Wholesale & retail | 2022 |
| Brecrest Sports Ltd | Wholesale & retail | 2014 |
| Bretts Country Restaurant Ltd | Hospitality | 2013 |
| Brianna Andone Ltd | Transport & logistics | 2015 |
| Bright & Sons (Solicitors) Limited | Professional & scientific | 2013 |
| Bright Control Systems Limited | Other services | 1997 |
| Bright Ideas (Maldon) Limited | Real estate | 2004 |
| Bright Metal Limited | Professional & scientific | 2000 |
| Brightspark, Plumbing, Heating and GAS Ltd | Construction | 2015 |
| Brimpton House Kelvedon Management Company Limited | Households | 2014 |
| Brisons Developments Ltd | Real estate | 2022 |
| Britanets Education Group Ltd | Education | 2023 |
| Britannia Liner Agencies Limited | Professional & scientific | 2004 |
| Broadacres Limited | Agriculture & fishing | 1994 |
| Broadgate Paper Co Limited | Administrative & support | 1996 |
| Broadway Painting Limited | Construction | 2005 |
| Brook Lyndhurst Limited | Professional & scientific | 1999 |
| Brookes Gallery (Guildford) Limited | Wholesale & retail | 2022 |
| Brookes Gallery Limited | Wholesale & retail | 2022 |
| Brookes Property Group Limited | Real estate | 2016 |
| Brookes Property International Ltd | Real estate | 2021 |
| Brookgate Management Company Limited | Households | 1982 |
| Brooks Bros. (Danbury) Limited | Wholesale & retail | 1997 |
| Brooks Bros. (Maldon) Limited | Wholesale & retail | 1975 |
| Brooks Bros. (NE) Limited | Wholesale & retail | 2010 |
| Brooks Bros. (UK) Limited | Wholesale & retail | 1982 |
| Brooks Bros.(Midlands) Limited | Manufacturing | 1989 |
| Brookside Care Solutions Ltd | Health & social care | 2024 |
| Brown Consult Ltd | Other services | 2022 |
| Bserv (Building Services) Limited | Construction | 2022 |
| BSG Supplies Limited | Wholesale & retail | 1987 |
| Buddy's Studio Ltd | Wholesale & retail | 2024 |
| Building Compliance Testing Limited | Professional & scientific | 2020 |
| Building Safety Services Ubique Ltd | Professional & scientific | 2023 |
| Bulk Haulage Group Limited | Financial services | 2019 |
| Bull & Sons Automation Limited | Construction | 2024 |
| Burlington Residential Ltd | Real estate | 2025 |
| Business Box Solutions Ltd | Information & communication | 2013 |
| Bytebuild Limited | Information & communication | 1997 |
| C & C Phiri Ltd | Real estate | 2023 |
| C & H Premier Homes Property Limited | Financial services | 2024 |
| C & M Precision Limited | Manufacturing | 2000 |
| C D Garden Maintenance (Essex) Limited | Administrative & support | 2016 |