| Beto Solutions Ltd | Health & social care | 2015 |
| Betta Aquatics Limited | Wholesale & retail | 2000 |
| Betterlife Properties Ltd | Real estate | 2007 |
| Betty Kermen Ltd | Real estate | 2023 |
| Beulah&H Limited | Health & social care | 2025 |
| Beulah's Decor Ltd | Hospitality | 2018 |
| BEV & Co Property Management Limited | Hospitality | 2014 |
| BG Mashine Limited | Other services | 2012 |
| BG Sports Ltd | Information & communication | 2025 |
| BGR Controls Limited | Construction | 2014 |
| Bhachu Holdings Ltd | Financial services | 2024 |
| Bhai Jaaan Ltd | Wholesale & retail | 2026 |
| Bhaijaans Biryani Restaurant Ltd | Hospitality | 2019 |
| Bhatti International Trading Ltd | Wholesale & retail | 2026 |
| Bhuiyan Group UK Ltd | Wholesale & retail | 2023 |
| Bibeuns of London Limited | Real estate | 1995 |
| BID Build Manage Limited | Professional & scientific | 2016 |
| Bids Rush Ltd | Wholesale & retail | 2025 |
| Bidwell (Machine Tools & Equipment) Limited | Wholesale & retail | 1979 |
| Bidwick Ltd | Real estate | 2003 |
| Bifrostix Technology Ltd | Administrative & support | 2025 |
| Big Bear Homes Ltd | Real estate | 2019 |
| Big Portion London Ltd | Hospitality | 2013 |
| Bikehead Ltd | Wholesale & retail | 2007 |
| Bikerpicsuk Ltd | Professional & scientific | 2025 |
| Bill Baylis Music Limited | Arts & recreation | 2001 |
| Billericay Golf Limited | Wholesale & retail | 2008 |
| Billet Auto Sales Limited | Wholesale & retail | 1977 |
| Billings Jenkins (BJ) Limited | Other services | 2024 |
| Billionaire Beach Club Ltd | Wholesale & retail | 2014 |
| Billiton Executive Pension Scheme Trustee Limited | Administrative & support | 1999 |
| Billy Bains Limited | Construction | 2008 |
| BIN Munir Ltd | Wholesale & retail | 2026 |
| Birch Airfield Composting Services Limited | Water & waste | 2007 |
| Birchrose Enterprises Limited | Hospitality | 2005 |
| Birchwood+ Management Ltd | Real estate | 2023 |
| Biryaani Boss Ltd | Hospitality | 2024 |
| Bishop Hall Properties Limited | Construction | 1994 |
| Bishop Stortford Developments Ltd | Construction | 2024 |
| Bishopric Limited | Construction | 2005 |
| Biyyk Ltd | Wholesale & retail | 2026 |
| Bizco Travels Limited | Transport & logistics | 2019 |
| Bizz Genius Limited | Information & communication | 2025 |
| BJB Holdings Limited | Professional & scientific | 1999 |
| BKZ Prestige Ltd | Wholesale & retail | 2025 |
| Black Birds Estates Ltd | Real estate | 2022 |
| Black Cat Energy Services Ltd | Mining & quarrying | 2007 |
| Black OPS Security Services Ltd | Financial services | 2026 |
| Blackbeam Consulting Ltd | Professional & scientific | 2026 |
| Blackbox Music Group Ltd | Information & communication | 2021 |
| Blackcat Automotive Limited | Transport & logistics | 2006 |
| Blackwater Consulting Limited | Professional & scientific | 2002 |
| Blackwater Property Group Limited | Real estate | 2025 |
| Blake Court Management Company Limited | Households | 1993 |
| Blakeana Developments Ltd | Construction | 2026 |
| Blakeana Holdings Ltd | Financial services | 2026 |
| Blakeana Properties Ltd | Real estate | 2025 |
| Blast Marketing Limited | Professional & scientific | 2007 |
| Blazex Ltd | Wholesale & retail | 2026 |
| Blendhold Limited | Professional & scientific | 1992 |
| Bliksem Geophysical Services Limited | | 1975 |
| Blind Cat Software Limited | Information & communication | 2023 |
| Bliss Event Hire Ltd | Hospitality | 2023 |
| Blissfy Ltd | Wholesale & retail | 2025 |
| BLM Plumbing Limited | Construction | 2020 |
| Block U.K. Limited | Administrative & support | 1996 |
| Blue Chip Event Security Ltd | Other services | 2019 |
| Blue Feather Network Ltd | Information & communication | 2025 |
| Blue Kite Management Ltd | Real estate | 2025 |
| Blue Planet Consulting Limited | Professional & scientific | 1998 |
| Blue Sapphire Hotel Ltd | Hospitality | 2021 |
| Blue Sky Education and Consultancy Ltd | Administrative & support | 2018 |
| Blue Whale HO Limited | Wholesale & retail | 2021 |
| Bluearc Global Ltd | Wholesale & retail | 2025 |
| Bluebeak Group Ltd | Information & communication | 2025 |
| Bluehouse Farm Community Centre Limited | Wholesale & retail | 2003 |
| Blueinc Support Services Limited | Other services | 2019 |
| Blueprint Collections Limited | Administrative & support | 1999 |
| Blueshine Limited | Hospitality | 2017 |
| Bluesky Electric Vehicles Ltd | Professional & scientific | 2009 |
| Bluestone Recovery London Ltd | Professional & scientific | 2023 |
| Bluetana Limited | Hospitality | 2022 |
| BM Estate Investments Limited | Real estate | 2024 |
| BM Heatelect Limited | Construction | 2021 |
| Bmarsh Computers Limited | Information & communication | 2007 |
| Bmcar Limited | Real estate | 1999 |
| BNM Scaffolding Ltd | Construction | 2025 |
| BO Medical Limited | Health & social care | 2025 |
| Boardnote Limited | | 1979 |
| Bobabbey Limited | Wholesale & retail | 1972 |
| Bobs OIL Boiler Service LLP | | 2002 |
| Bodhill Limited | | 1986 |
| Body Jewels Limited | Wholesale & retail | 2005 |
| Bodycare Personal Fitness Club Limited | Arts & recreation | 2004 |
| Bohbupmed Limited | Health & social care | 2024 |
| Bolbless UK Limited | Health & social care | 2016 |
| Boldea Ltd | Construction | 2019 |
| Boldpixel Ltd | Information & communication | 2026 |
| Bomoco Limited | Wholesale & retail | 1992 |
| Bonds of Essex Ltd | Real estate | 2018 |