| Black Sheep Operations Limited | Professional & scientific | 2022 |
| Black Stock Barber Ltd | Other services | 2026 |
| Black Swan (Jackfield) Ltd | Hospitality | 2003 |
| Black Women's Resource Centre Watoto Preschool | Education | 2006 |
| Black Wood Music Limited | Information & communication | 2012 |
| Blacka Moor Gardens Management Company Limited | Households | 2016 |
| Blackamoor Developments Limited | Construction | 2025 |
| Blackamoor Estates Limited | Real estate | 2016 |
| Blackamoor Limited | Real estate | 2011 |
| Blackbird Creative Studio Ltd | Arts & recreation | 2023 |
| Blackbull Ecclesfield Ltd | Hospitality | 2024 |
| Blackburn and Wincobank Conservative Club Limited(The) | Other services | 1899 |
| Blackburn Products Company Limited | Extraterritorial | 1919 |
| Blackest Rainbow Ltd | Wholesale & retail | 2016 |
| Blackfortz Capital Ltd | Professional & scientific | 2024 |
| Blackfriars 1962 Ltd | Professional & scientific | 2024 |
| Blackgreen Limited | Arts & recreation | 2016 |
| Blackhouse Rock Ltd | Hospitality | 2019 |
| Blackjack Buildings Ltd | Real estate | 2021 |
| Blackjackal Limited | Information & communication | 2011 |
| Blacklight Consulting Limited | Construction | 2006 |
| Blackmoor Croft Health Care Limited | Health & social care | 2019 |
| Blackmoor Farm Management Company Ltd | Real estate | 2020 |
| Blacksheepinc Limited | Wholesale & retail | 2025 |
| Blacksmith by Design Ltd | Manufacturing | 2024 |
| Blacksmith House Coaching & Consulting Ltd | Administrative & support | 2022 |
| Blackstock Road Nisa Local Limited | Wholesale & retail | 2025 |
| Blackstock Superstore Ltd | Wholesale & retail | 2026 |
| Blackstone Business Finance Ltd | Financial services | 2008 |
| Blackstone International Investments LLP | | 2012 |
| Blackstone Marketing Ltd | Professional & scientific | 2026 |
| Blackstone Property (Hallam) Limited | Construction | 2026 |
| Blackstone Sports Group Ltd | Arts & recreation | 2021 |
| Blackswan 2020 Limited | Manufacturing | 2020 |
| Blackswan Linen Ltd | Administrative & support | 2021 |
| Blackthorn Analytics Ltd | Financial services | 2025 |
| Blackthorne Building & Design Ltd | Construction | 2006 |
| Blackthorne Utilities Limited | Administrative & support | 2013 |
| Blacktip Design Limited | Arts & recreation | 2011 |
| Blacktree Data Ltd | Administrative & support | 2025 |
| Blackwater Properties Limited | Real estate | 1972 |
| Blackwell & SON Ltd | Real estate | 2025 |
| Blade Leasing Co Limited | Professional & scientific | 2006 |
| Blade Wheels Ltd | Transport & logistics | 2024 |
| Bladerunners Peaks Limited | Other services | 2012 |
| Blades Leisure Limited | Financial services | 2009 |
| Blades Power Services Limited | Construction | 2023 |
| Blake Coaching Limited | Other services | 2022 |
| Blakeward Limited | Hospitality | 2018 |
| Blanco Music Limited | Information & communication | 1999 |
| Blanco Y Negro Limited | Extraterritorial | 1983 |
| Blandygam Holdings Limited | Financial services | 2026 |
| Blank Record Limited | Manufacturing | 2017 |
| Blanket Studio Ltd | Professional & scientific | 2022 |
| Blanks 3D Ltd | Manufacturing | 2024 |
| Blastcom (U.K.) Limited | Wholesale & retail | 1996 |
| Blastech Limited | Professional & scientific | 2003 |
| Blastore Holdings Ltd | Financial services | 2025 |
| Blaydon Storage Limited | Transport & logistics | 2024 |
| Blaze Community Foundation | Arts & recreation | 2008 |
| BLB Communications Limited | Administrative & support | 2021 |
| BLB Developments (Yorkshire) Limited | Real estate | 2005 |
| BLE (Holdings) Limited | Professional & scientific | 1995 |
| BLE Lighting and Power Limited | Manufacturing | 1968 |
| BLE Smoke and Fire Curtains Limited | Manufacturing | 2004 |
| Bleach LAB Limited | Information & communication | 2017 |
| Bleak House Holdings Limited | Financial services | 2026 |
| Bleak House Limited | Hospitality | 1997 |
| Bledea Parts Ltd | Construction | 2022 |
| Blend Community CIC | Hospitality | 2024 |
| Blend Deansgate Ltd | Hospitality | 2025 |
| Blend E&C London Ltd | Hospitality | 2025 |
| Blend Factory Works Ltd | Hospitality | 2024 |
| Blend Family Ltd | Financial services | 2023 |
| Blend Made Ltd | Construction | 2024 |
| Blend Manchester Printworks Ltd | Hospitality | 2026 |
| Blend Nottingham Victoria Ltd | Hospitality | 2025 |
| Blenheim Developments Sheffield Limited | Construction | 2020 |
| Blenheim Heights Commercial Limited | Real estate | 2023 |
| Blenheim Land & Properties Ltd | Real estate | 2009 |
| Blenheim Mews (Sheffield) Limited | Households | 2005 |
| Blenheim Park Estates Ltd | Construction | 2020 |
| Blenhiem Motor's Ltd | Wholesale & retail | 2019 |
| Blenstone Limited | Administrative & support | 2000 |
| Bles Property Rentals and Services Ltd | Real estate | 2024 |
| Blessedduo Limited | Extraterritorial | 2018 |
| Blessmart Ltd | Other services | 2026 |
| Blessone's Kitchen Limited | Hospitality | 2017 |
| Bletchley Financial Ltd | Financial services | 2021 |
| Bletchley Park Consulting Limited | Professional & scientific | 2009 |
| BLH Ltd | Information & communication | 2019 |
| Blimsy Ltd | Wholesale & retail | 2025 |
| Blina Limited | Manufacturing | 2020 |
| Blind Beauty (Yorkshire) Limited | Administrative & support | 2006 |
| Blind Beauty Limited | Manufacturing | 2003 |
| Blind Inspiration Somerset Limited | Wholesale & retail | 2015 |
| Blind Mice Media Limited | Information & communication | 2007 |
| Blinds 4 Home Limited | Construction | 2022 |
| Blinds Expert Ltd | Wholesale & retail | 2019 |
| Blindsco Ltd | Wholesale & retail | 2012 |