| Black Zebra London Limited | Wholesale & retail | 2024 |
| Blackbox Entertainment Ltd | Wholesale & retail | 2013 |
| Blackcurrant Contract Solutions Limited | Professional & scientific | 2017 |
| Blackmoor Knight Ltd | Construction | 2006 |
| Blackmore Commercial Group Ltd | Construction | 2025 |
| Blackmore Property Group Ltd | Real estate | 2021 |
| Blackton Services Limited | Administrative & support | 2018 |
| Blackwood & Hall Ltd | Construction | 2014 |
| Blackwood and Hall Engineering Ltd | Construction | 2025 |
| Block Elite Projects Ltd | Construction | 2025 |
| Blokus Family Ltd | Administrative & support | 2025 |
| Bloomfield Deliveries Ltd | Wholesale & retail | 2002 |
| BLU Willow Properties Limited | Real estate | 2022 |
| Blue Checkbox Ltd | Information & communication | 2010 |
| Blue Door Homes Limited | Construction | 2005 |
| Blue FOG Limited | Professional & scientific | 2025 |
| Blue Haven Assets Limited | Financial services | 2022 |
| Blue Q Capital Ltd | Real estate | 2022 |
| Blue Shells Boutique Ltd | Wholesale & retail | 2026 |
| Blue Sky Property Solutions South East Ltd | Construction | 2016 |
| Blue Sky Security Services Limited | Administrative & support | 2018 |
| Blue Sky Security Solutions Limited | Administrative & support | 2018 |
| Blue Sky Security Systems Limited | Administrative & support | 2003 |
| Blue(Sussex) Ltd | Administrative & support | 2019 |
| Bluebell and Robin Gardens Limited | Administrative & support | 2021 |
| Bluebell Projects (Essex) Limited | Construction | 2022 |
| Bluebells Catering Ltd | Hospitality | 2020 |
| Blueprint Construction Herts Ltd | Construction | 2026 |
| Blueprint Construction Ltd | Construction | 2019 |
| Blueqmortgage Ltd | Financial services | 2005 |
| Blumarble Capital Limited | Financial services | 2012 |
| Blumarble Property Limited | Real estate | 2014 |
| Bmjcontractors Ltd | Manufacturing | 2021 |
| Boardfine Limited | Other services | 1998 |
| Bobby Kamal Limited | Administrative & support | 2019 |
| Bobson Concept Ltd | Professional & scientific | 2014 |
| Boca Construction Limited | Construction | 2012 |
| Bodymech Consulting Limited | Professional & scientific | 2025 |
| Boiler Assist Ltd | Financial services | 2025 |
| Bolthouse Ltd | Real estate | 2020 |
| Bond Mckenzie Limited | Administrative & support | 2008 |
| Bondpro Ltd | Construction | 2024 |
| Bonnbell Estates Limited | Real estate | 2020 |
| BOO & Kins Ltd | Other services | 2025 |
| Boomflow Property Limited | Real estate | 2023 |
| Boomflow Services Limited | Administrative & support | 2024 |
| Boraes Ltd | Real estate | 2025 |
| Bosenn Properties Limited | Real estate | 2026 |
| Boss Group Services Limited | Administrative & support | 2025 |
| Boss Paint Finishers Ltd | Wholesale & retail | 2018 |
| Boss Waste Ltd | Administrative & support | 2019 |
| Boss Waste Management Ltd | Water & waste | 2021 |
| Bottomlip Tackle Limited | Wholesale & retail | 2014 |
| Boundless Clean Ltd | Administrative & support | 2025 |
| Bounty Ltd | Real estate | 2024 |
| BOV Engineering Ltd | Construction | 2020 |
| Bowden Group Holdings Limited | Financial services | 2023 |
| Bowden Property Holdings Ltd | Real estate | 2024 |
| Bowden Property Services Limited | Real estate | 2022 |
| Bowlane Properties Ltd | Real estate | 2007 |
| Box Events Ltd | Arts & recreation | 2011 |
| Boxed UP Media Limited | Information & communication | 2014 |
| BP Jenkins Ltd | Information & communication | 2022 |
| BP Security Ltd | Administrative & support | 2026 |
| Bpmt Growth Strategy Limited | Extraterritorial | 2016 |
| Bpmt Ltd | Financial services | 2021 |
| Brace Productions Limited | Professional & scientific | 2012 |
| Bradshaw Pearson Limited | Information & communication | 2019 |
| Bramston Brook Limited | Professional & scientific | 2001 |
| Bramston Property Limited | Professional & scientific | 2002 |
| Bran Investments Limited | Financial services | 2016 |
| Branching OUT Careers C.I.C. | Education | 2018 |
| Brand Dine Ltd | Hospitality | 2019 |
| Branded Trading Limited | Wholesale & retail | 2010 |
| Brandingplus South Essex Ltd | Wholesale & retail | 2001 |
| Brandlife Limited | Administrative & support | 2002 |
| Brando Productions UK Limited | Information & communication | 2005 |
| BRE Services Limited | Wholesale & retail | 2022 |
| Brentor Consultants Limited | Professional & scientific | 2019 |
| Brentwood Beauty Ltd | Other services | 2019 |
| Brentwood Lashes Training Academy Ltd | Education | 2020 |
| Briar Health Ltd | Health & social care | 2024 |
| Brick Lane Bagel Co Boxpark Croydon Ltd | Hospitality | 2024 |
| Brick Lane Bagel Co Freeport Ltd | Hospitality | 2024 |
| Brick Lane Bagel O2 Limited | Hospitality | 2022 |
| Brick Lane Bagel Westfield Ltd | Hospitality | 2022 |
| Bridger Consulting Ltd | Information & communication | 2012 |
| Bright Mortgage Services Limited | Financial services | 2014 |
| Bright Star Financial Limited | Financial services | 2010 |
| Brighter Future Cleaning Ltd | Administrative & support | 2023 |
| Brightside CX Consulting Ltd | Information & communication | 2016 |
| Brightsky Technology Ltd | Professional & scientific | 2024 |
| Britmod Studio Ltd | Arts & recreation | 2023 |
| Broadtech Network Solutions Limited | Administrative & support | 2010 |
| Broadway Assets Limited | Construction | 2018 |
| Brook Forwarding Limited | Professional & scientific | 2015 |
| Broomhills Cockapoos Limited | Agriculture & fishing | 2020 |
| BSS Fibre Ltd | Information & communication | 2022 |
| Bucharest Restaurants Limited | Hospitality | 2019 |
| Building Design Consultants Limited | Construction | 2013 |