| Bahar-E-Madina | Professional & scientific | 2013 |
| BAJ Coatings Limited | Extraterritorial | 1958 |
| Baker Property Services Ltd | Construction | 2022 |
| Baker's Boxes Ltd | Wholesale & retail | 2023 |
| Bakers Place Management Company Limited | Households | 2016 |
| Bakery Mews RTE Company Limited | Extraterritorial | 2009 |
| Bakery Mews RTM Company Limited | Households | 2007 |
| Balintax Ltd | Transport & logistics | 2018 |
| Balkin Nutrition Ltd | Professional & scientific | 2026 |
| Ballista Ltd | Information & communication | 2019 |
| Ballot Ltd | Information & communication | 2026 |
| BAM Construct & Ventures UK Limited | Construction | 1997 |
| BAM Construction Limited | Construction | 1989 |
| BAM Design Limited | Professional & scientific | 1982 |
| BAM Glory Mill Limited | Real estate | 2006 |
| BAM Infrastructure Limited | Construction | 2005 |
| BAM Properties Limited | Real estate | 1996 |
| BAM Site Solutions Limited | Construction | 1959 |
| BAM TCP Atlantic Square Limited | Construction | 2001 |
| BAM UK & Ireland Enabling Services Limited | Administrative & support | 2024 |
| Bamboosh Limited | Real estate | 2016 |
| Bamford Technical Services Ltd | Wholesale & retail | 2024 |
| Bancroft Management Company Limited | Households | 2006 |
| Bannard Property Services Limited | Administrative & support | 2010 |
| Baotinermi Ltd | Hospitality | 2017 |
| Barbers 101 Ltd | Other services | 2020 |
| Barbican Management Company Limited | Real estate | 2004 |
| Barclay for Business Ltd | Public administration | 2025 |
| Bard Property Bidco Ltd | Financial services | 2023 |
| Bard Property Midco Ltd | Financial services | 2023 |
| Bardolin Limited | | 1920 |
| BARI2TA'S Limited | Hospitality | 2019 |
| Barista's Limited | Hospitality | 2008 |
| BARISTA’3 Limited | Hospitality | 2019 |
| Barkers Management Limited | Households | 2007 |
| Barking Brilliant Ltd | Information & communication | 2010 |
| Barkway Group Limited | Real estate | 2008 |
| Barley Fields Management Company Limited | Households | 2016 |
| Barley Meadows (Southminster) Management Company Limited | Households | 2014 |
| Barley Mews Management Company Limited | Construction | 1993 |
| Barmouth Bay Holiday Park Limited | Hospitality | 2013 |
| BARN112 Limited | Professional & scientific | 2008 |
| Barndello Consulting Limited | Professional & scientific | 2019 |
| Barnes Renewables Ltd | Real estate | 2021 |
| Barnet Theatre School LLP | | 2024 |
| Barnett's Coaches Ltd | Transport & logistics | 2005 |
| Barnrestore Limited | Construction | 2016 |
| BARO18 Limited | Hospitality | 2026 |
| Barrington Court (RTM) Company Limited | Households | 2003 |
| Barsotti's Food Ltd | Hospitality | 2022 |
| Bart Electrical Services Ltd | Construction | 2023 |
| Barton Corporation Ltd | Construction | 2001 |
| Barton Park (Oxford Phase 2, Phase 4A and Phase 4B) Estate Management Company Limited | Households | 2023 |
| Barton Residential Limited | Real estate | 2022 |
| Base One Cafe Ltd | Hospitality | 2023 |
| Basel UK Acquisition Co. Limited | Financial services | 2022 |
| Bashir Sons Global Ltd | Wholesale & retail | 2024 |
| Bashk Novo Commerce Ltd | Wholesale & retail | 2025 |
| Bassmead INV Ltd | Real estate | 2023 |
| Bastion Construction Ltd | Construction | 2015 |
| Bastwick Flat Management Limited | Households | 2011 |
| Batchelor GAS & Heating Ltd | Construction | 2018 |
| Batchwood Developments Ltd | Real estate | 2017 |
| Bath and Stone Ltd | Construction | 2024 |
| Batos Limited | Construction | 2025 |
| Battle Holdings Limited | Real estate | 2016 |
| Bausen Limited | Wholesale & retail | 1987 |
| Baweja London Ltd | Wholesale & retail | 2019 |
| Bawtrys Estate Management Limited | Households | 2019 |
| Baye Capital LLP | | 2023 |
| Bazil Ltd | Wholesale & retail | 2025 |
| BB Cakes Ltd | Manufacturing | 2015 |
| BB Plumbing & Heating Services Ltd | Construction | 2017 |
| BBB Builders Ltd | Construction | 2025 |
| Bbb(London) Limited | Construction | 2013 |
| BBM Electrical Services Limited | Construction | 2012 |
| BC Automation Ltd | Information & communication | 2024 |
| BCC Property Lettings Ltd | Real estate | 2025 |
| BCK Services Limited | Administrative & support | 2022 |
| BD Property Group Ltd | Real estate | 2017 |
| BDN Consulting Limited | Information & communication | 2025 |
| BE Consulting Partners Limited | Administrative & support | 2018 |
| BE My Beauty Clinic Ltd | Other services | 2023 |
| Beaconsfield Short Stays Ltd | Real estate | 2020 |
| Beaconstone Construction Services Ltd | Construction | 2020 |
| Beamac Associates Limited | Wholesale & retail | 2012 |
| Bear Building Services Limited | Professional & scientific | 2020 |
| Bearman Law LLP | | 2013 |
| Beart & Gibson Limited | Construction | 1997 |
| Beaufoy Services Ltd | Information & communication | 2021 |
| Beaulieu Grange (Chelmsford) Management Company Limited | Real estate | 2022 |
| Beaumont Place Management Limited | Households | 2012 |
| Beauty by Emily Ltd | Other services | 2022 |
| Beautyspauk Limited | Other services | 2021 |
| Beba Energy UK Ltd | Energy | 2009 |
| Beck Optronic Solutions Limited | Manufacturing | 2014 |
| Bedeau Russell Consulting Limited | Professional & scientific | 2026 |
| Bedford Valeting Limited | Wholesale & retail | 2023 |
| Bedrock Productions Limited | Information & communication | 2011 |
| Bedwell Hall Limited | Households | 2011 |