| BAS Solutions Limited | Construction | 2020 |
| Baseline Creative Limited | Professional & scientific | 1984 |
| Basil's Kitchen Limited | Hospitality | 2025 |
| BAT Speed Limited | Transport & logistics | 2021 |
| Bathrooms of Cowbridge Ltd | Construction | 2023 |
| Batri Limited | Manufacturing | 2020 |
| Bay Developments (2016) Limited | Construction | 2016 |
| Bay:K Limited | Extraterritorial | 2022 |
| Baydean Limited | Extraterritorial | 2024 |
| Baykar Food Ltd | Hospitality | 2025 |
| BB & DB Consultancy Services Limited | Professional & scientific | 2025 |
| Bbhs Limited | Construction | 2000 |
| BCP Specialists Limited | Wholesale & retail | 2008 |
| BD Carr Limited | Construction | 2007 |
| BE Wise Business Solutions Ltd | Financial services | 2025 |
| Beach Court, Saundersfoot, Management Company Limited | Households | 2007 |
| Beacon Roofing Limited | Construction | 1993 |
| Beames Consulting Ltd | Professional & scientific | 2024 |
| Bear HUG TV Limited | Information & communication | 2014 |
| Beardo Gets Scared Limited | Information & communication | 2024 |
| Bearslogistics CYF | Transport & logistics | 2017 |
| Beasted Ltd | Arts & recreation | 2018 |
| Beautiful YOU UK Limited | Other services | 2018 |
| Beautybargainz Ltd | Wholesale & retail | 2025 |
| Because WE Care Northampton Ltd. | Other services | 2015 |
| Becky Matthews Writing Ltd | Other services | 2017 |
| Becky Preece Consult Ltd | Education | 2026 |
| Bedford Road Property Wales Ltd | Households | 2025 |
| Beech Regeneration Limited | Real estate | 2016 |
| Beer Barrels & Minerals (Wales) Limited | Wholesale & retail | 1995 |
| Behind the Pour Ltd | Hospitality | 2025 |
| Bella Beaute Make UP Studios Ltd | Other services | 2018 |
| Bellaboo Boutique Limited | Wholesale & retail | 2021 |
| Belleair Ltd | Manufacturing | 2026 |
| Belledge Limited | Wholesale & retail | 2020 |
| Bellissimo B Limited | Other services | 2016 |
| Bellrate Limited | Extraterritorial | 2025 |
| BEN Board Construction Management Ltd | Professional & scientific | 2020 |
| BEN Cruise Holdings Limited | Real estate | 2014 |
| Benabi Solutions Limited | Real estate | 2021 |
| Benelux Ltd | Hospitality | 2014 |
| Benjamin Stone Music Ltd | Arts & recreation | 2024 |
| Benk Limited | Information & communication | 2016 |
| Bennetts Engineering Services Ltd | Construction | 2023 |
| Benni Homes Ltd | Real estate | 2025 |
| Berranevra Ltd | Hospitality | 2025 |
| Berrow Property Holdings Ltd | Real estate | 2025 |
| Berryhorse Ltd | Manufacturing | 2010 |
| Bespoke Dignified Services Limited | Other services | 2013 |
| Bespoke UK Holdings Ltd | Manufacturing | 2025 |
| Bespoke-Uk Ltd | Manufacturing | 2015 |
| Besst Tyres Limited | Wholesale & retail | 2004 |
| Betts Publications Ltd | Professional & scientific | 2023 |
| Bettws F.C. Limited | Education | 2020 |
| Bettws Service Station Limited | Wholesale & retail | 2020 |
| Bevan College Ltd | Education | 2023 |
| Bevan Developments Limited | Construction | 2023 |
| BFL Engineering Services Ltd | Construction | 2006 |
| Bfxcapital Ltd | Financial services | 2017 |
| BGK Pyle Limited | Financial services | 2023 |
| Big Bocs Self Storage Ltd | Administrative & support | 2022 |
| Big Brothers Bridgend Ltd | Hospitality | 2026 |
| Billflip Ltd | Professional & scientific | 2025 |
| Biohack Gold Ltd | Wholesale & retail | 2026 |
| Biomet UK Healthcare Limited | Health & social care | 2009 |
| Biomonde Limited | Financial services | 2021 |
| Biomonde Technology Limited | Administrative & support | 2024 |
| Bipmark Limited | Real estate | 2022 |
| Birchgrove Design Limited | Administrative & support | 2012 |
| Birchway Limited | Professional & scientific | 2018 |
| Birchwood Portable Accommodation Limited | Hospitality | 2005 |
| Birmingham Properties & Investment Co.Limited | Construction | 1959 |
| Birr Enterprises Limited | Extraterritorial | 2017 |
| Birr Formations Limited | Professional & scientific | 2000 |
| Birr Legal Services Limited | Real estate | 2009 |
| Birr Nominees Limited | Professional & scientific | 2000 |
| Birr Secretaries Limited | Professional & scientific | 2000 |
| Bit-Soft Technology Ltd | Information & communication | 2026 |
| Bizrisk Limited | Administrative & support | 2006 |
| Bizzi Day Nurseries Limited | Education | 2012 |
| BJE Developments Limited | Real estate | 2000 |
| Bjorntjie Limited | Health & social care | 2024 |
| Bjpeye Ltd | Health & social care | 2024 |
| BK Decorating Ltd | Construction | 2023 |
| BKB Automotive Ltd | Wholesale & retail | 2020 |
| Black Canaries Ltd | Information & communication | 2020 |
| Black Cat Traders Limited | Hospitality | 2022 |
| Blacklock NON Destructive Testing Ltd | Administrative & support | 2015 |
| Blackout Barbers Ltd | Other services | 2023 |
| Blacktaff Ltd | Wholesale & retail | 2025 |
| Blackthorn Court Financial Ltd | Financial services | 2021 |
| Blaencrymlyn Properties Limited | Real estate | 2024 |
| Blaengarw Cricket Club Ltd | Arts & recreation | 2025 |
| Blaenogwr Hotel Limited | Construction | 2021 |
| Blakedon Limited | Construction | 2025 |
| BLG48PH Ltd | Transport & logistics | 2018 |
| Blitz Hospitality Academy Limited | Information & communication | 2017 |
| Block and Bridge Strategy Ltd | Professional & scientific | 2025 |
| Blockuno Ltd | Information & communication | 2021 |
| Blue Dragon Essentials Limited | Wholesale & retail | 2007 |