| Books Plus Cardiff Limited | Wholesale & retail | 2020 |
| Boom and Done Ltd | Transport & logistics | 2024 |
| Boom Cymru TV Ltd | Information & communication | 1994 |
| Boom Pro Ltd | Wholesale & retail | 2015 |
| Boomerang Developments Ltd | Administrative & support | 2017 |
| Boomerang Lounges Cardiff Ltd | Hospitality | 2024 |
| Boomrang Limited | Hospitality | 2010 |
| Boontr Limited | Wholesale & retail | 2025 |
| Boost Direct Limited | Professional & scientific | 2021 |
| Boost Live Limited | Information & communication | 2025 |
| Boost Your Tribe Ltd | Professional & scientific | 2019 |
| Boostbredda Ltd | Information & communication | 2025 |
| Booster Education Ltd | Extraterritorial | 2021 |
| Boostravel Ltd | Professional & scientific | 2023 |
| Booth Atlantic Limited | Hospitality | 2004 |
| Booth Group Leisure & Hospitality Limited | Professional & scientific | 2016 |
| Booth Group Ventures Limited | Real estate | 2017 |
| Bootham Enterprises Ltd | Wholesale & retail | 2023 |
| Bootle PTY Ltd | Wholesale & retail | 2020 |
| Bootlegger Bars Limited | Hospitality | 2016 |
| Bopbumpbounceevents Ltd | Arts & recreation | 2025 |
| Boptics Limited | Health & social care | 2010 |
| Bora Commerce Ltd | Wholesale & retail | 2025 |
| Borahaspe Limited | Manufacturing | 2023 |
| Borden Lane Ltd | Real estate | 2023 |
| Border Worldwide Drinks Ltd | Hospitality | 2020 |
| Border-Clash C.I.C. | Education | 2025 |
| Borderknot Limited | Households | 1979 |
| Borderless Bazaar Ltd | Wholesale & retail | 2025 |
| Bordew Limited | Professional & scientific | 2019 |
| Boreal Nest Saas Ltd | Information & communication | 2025 |
| Bored Sellers Ltd | Wholesale & retail | 2020 |
| Borehaven Saas Limited | Information & communication | 2025 |
| Borfreight Ltd | Transport & logistics | 2020 |
| Borg Estates Limited | Real estate | 2021 |
| Borges Services Ltd | Other services | 2020 |
| Borgo Ltd | Hospitality | 2020 |
| Borica JR Ltd | Transport & logistics | 2025 |
| Borja Jewellers Limited | Other services | 2019 |
| Bork Medicine and Vitamins Ltd | Manufacturing | 2021 |
| Borki Ltd | Information & communication | 2015 |
| Borley Associates Limited | Construction | 2020 |
| Borley Engineering Services Limited | Construction | 1992 |
| Borley Holdings Limited | Financial services | 2020 |
| Borley Medical Ltd | Health & social care | 2017 |
| Borley Property Investments Limited | Real estate | 2001 |
| Borley Property Management Limited | Real estate | 2015 |
| Born Happy Ltd | Wholesale & retail | 2010 |
| Born in a Storm Ltd | Wholesale & retail | 2022 |
| Born in ME Productions Limited | Information & communication | 2020 |
| Bornal Corporate PC | | 2018 |
| Borne Promotions Limited | Other services | 2017 |
| Borntrappy Ltd | Information & communication | 2022 |
| Boro Digital Dynamics Ltd | Information & communication | 2023 |
| Borras&Co Ltd | Wholesale & retail | 2026 |
| Borrell Properties Ltd | Real estate | 2020 |
| Borth Pharmacy Limited | Wholesale & retail | 2002 |
| Borz Ltd | Wholesale & retail | 2025 |
| Bos-Uie Limited | Energy | 1972 |
| Bosal Enterprises Limited | Other services | 2018 |
| Bosnian Voyager Ltd | Administrative & support | 2025 |
| Bosphorus Underground Ltd | Wholesale & retail | 2025 |
| Boss & Brew Academy C.I.C. | Hospitality | 2021 |
| Boss Building & DIY Supplies Ltd | Wholesale & retail | 2022 |
| Boss House Ltd | Real estate | 2021 |
| Boss House Management Company Limited | Households | 1995 |
| Boss Life Ltd | Wholesale & retail | 2023 |
| Boss Wallet Limited | Information & communication | 2025 |
| Boss Your Life Ltd. | Professional & scientific | 2017 |
| Bosselec Limited | Construction | 2018 |
| Bossnet Ltd | Administrative & support | 2018 |
| Boston House Investments 1 Limited | Construction | 2019 |
| Boston House Investments 2 Limited | Construction | 2023 |
| Boston International Company Ltd | Wholesale & retail | 2024 |
| Boston Media Communication Ltd | Wholesale & retail | 2021 |
| Boston Trading Limited | Extraterritorial | 2019 |
| Boston UK Courier Service Ltd | Transport & logistics | 2024 |
| BOT Accounting Ltd | Professional & scientific | 2021 |
| Botanico Cuisine Limited | Hospitality | 2025 |
| Bots for That Ltd | Information & communication | 2013 |
| Bottom Line Consultants Ltd | Other services | 2016 |
| BOU Properties Ltd | Households | 2019 |
| BOU Recruitment Ltd | Administrative & support | 2020 |
| Boudety Co., Ltd | Wholesale & retail | 2021 |
| Boudoir-Secrets Ltd | Wholesale & retail | 2003 |
| Bouff Ltd | Other services | 2017 |
| Boujee Drinks Ltd | Wholesale & retail | 2019 |
| Boujewels Limited | Wholesale & retail | 2024 |
| Boulton & Griffiths - Professionals Relocating Limited | Real estate | 2006 |
| Bounce International Ltd | Professional & scientific | 2016 |
| Bouncy Bees Bouncy Castle Hire Ltd | Administrative & support | 2023 |
| Boundary Developments Limited | Administrative & support | 2002 |
| Boundless Studio Ltd | Information & communication | 2023 |
| Bouom Company Ltd | Wholesale & retail | 2024 |
| Bournbuild Limited | Construction | 2016 |
| Bourne Systems Limited | Other services | 2010 |
| Bournecool Limited | Construction | 2010 |
| Bournegrove Financial Planning Limited | Financial services | 2017 |
| Boutique 53 Ltd | Wholesale & retail | 2015 |
| Boutique Occasions Ltd | Wholesale & retail | 2020 |