| Black Water Chauffeurs Ltd | Transport & logistics | 2025 |
| Black's Design Services Limited | Professional & scientific | 1988 |
| Blackb Financial Services Limited | Financial services | 2017 |
| Blackberry Close Management Limited | Administrative & support | 2025 |
| Blackberry Finance Solutions Limited | Financial services | 2007 |
| Blackbriar Plant Hire Ltd | Administrative & support | 2022 |
| Blackbuck Acquisitions Limited | Financial services | 2017 |
| Blackdombo International Ltd | Professional & scientific | 2021 |
| Blackhawk Private Limited | Administrative & support | 2025 |
| Blackjack Shops Limited | Hospitality | 2025 |
| Blackpool Food & Beverages Limited | Wholesale & retail | 2010 |
| Blackshore (Holdings) Limited | Other services | 2024 |
| Blackstar Trading Ltd | Wholesale & retail | 2025 |
| Blackstone Building & Construction Limited | Construction | 2023 |
| Blackstone Financial & Tax Advisors Limited | Professional & scientific | 2025 |
| Blackstone Global Group Ltd | Other services | 2020 |
| Blackstone Investment Holdings Ltd | Real estate | 2025 |
| Blackstone Legal & Marketing Consultants Ltd | Professional & scientific | 2025 |
| Blackstone Vetting Ltd | Information & communication | 2026 |
| Blackstone Wealth Ltd | Financial services | 2022 |
| Blackthorn Construction Group Ltd | Construction | 2022 |
| Blackthorne Industries Ltd | Professional & scientific | 2025 |
| Blackwood Blinds Limited | Manufacturing | 2000 |
| Blackwood Executive Travel Ltd | Transport & logistics | 2026 |
| Blade Security Services Limited | Administrative & support | 2020 |
| Blaithin Limited | Professional & scientific | 2017 |
| Blake and Brown Ltd | Agriculture & fishing | 2020 |
| Blake Global Holdings Ltd | Wholesale & retail | 2026 |
| Blana Painting & Decorating Ltd | Construction | 2020 |
| Blandford Properties Ltd | Real estate | 2023 |
| Blaque Edmonds Ltd | Wholesale & retail | 2020 |
| Blastbusters Ltd | Administrative & support | 2020 |
| Blastim Ltd | Administrative & support | 2020 |
| Blazon Studios Limited | Manufacturing | 2014 |
| BLB Brickwork Limited | Construction | 2024 |
| Bledi M.L Transport Limited | Transport & logistics | 2024 |
| Bledi Painting & Decorating Ltd | Construction | 2024 |
| Bleep Care Limited | Health & social care | 2013 |
| Blench Skip Hire Ltd | Water & waste | 2025 |
| Blend Bazaar Limited | Wholesale & retail | 2024 |
| Blendz Limited | Other services | 2016 |
| Blessed IS OUR Hands Limited | Health & social care | 2020 |
| Bleu Signal Ltd | Information & communication | 2026 |
| Blip Discs Limited | Information & communication | 2016 |
| Blip Driver Training Ltd | Education | 2023 |
| Bliss Beauty Salon Luton Limited | Other services | 2020 |
| Bliss Boutique Luton Limited | Wholesale & retail | 2024 |
| Blissbee Nature Private Limited | Wholesale & retail | 2025 |
| Blissful Luxury Ltd | Hospitality | 2023 |
| Blissings Limited | Wholesale & retail | 2021 |
| Blizz Healthcare Limited | Health & social care | 2022 |
| Block a Millennium Drive Management Company Limited | Households | 2000 |
| Block Bazzar Limited | Health & social care | 2020 |
| Blocks Direct Ltd | Manufacturing | 2025 |
| Bloodline Homes Ltd | Households | 2025 |
| Bloom and Create CIC | Arts & recreation | 2025 |
| Bloom and Stitch CIC | Education | 2025 |
| Bloomed Limited | Health & social care | 2013 |
| Bloomhurst Services Ltd | Transport & logistics | 2013 |
| Blooming Valley Limited | Wholesale & retail | 2025 |
| Blooming Wild Ltd | Health & social care | 2021 |
| Bloomwise Cleaners Limited | Administrative & support | 2026 |
| Bloomyy Ltd | Health & social care | 2024 |
| Blossom Advanced Care Services Ltd | Health & social care | 2020 |
| Blossom Beauty Studio Limited | Wholesale & retail | 2019 |
| Blossom Fostering Services Limited | Health & social care | 2021 |
| Blossom Hill Care and Support Services Ltd | Hospitality | 2024 |
| Blossom Hill Support Services Limited | Hospitality | 2024 |
| Blossom Homes (Beds) Ltd | Health & social care | 2026 |
| Blossome Care Limited | Health & social care | 2024 |
| BLR Group Limited | Wholesale & retail | 2022 |
| Blue Catering Services Limited | Hospitality | 2019 |
| Blue Drive Limited | Wholesale & retail | 2025 |
| Blue Driving Ltd | Education | 2025 |
| Blue Economy Solution Limited | Professional & scientific | 2022 |
| Blue Express Courier Limited | Transport & logistics | 2023 |
| Blue Flame Plumbing&Heating Ltd | Construction | 2023 |
| Blue Horizon HR Limited | Administrative & support | 2024 |
| Blue Horse Logistics Ltd | Wholesale & retail | 2021 |
| Blue India Takeaway Ltd | Hospitality | 2023 |
| Blue Iroko Ltd | Health & social care | 2021 |
| Blue Line Customs Limited | Wholesale & retail | 2022 |
| Blue Lion London Limited | Real estate | 2025 |
| Blue Lotus Properties Ltd | Real estate | 2023 |
| Blue Mountain Shipping Company Ltd | Other services | 2019 |
| Blue Orchid Aspley Guise Ltd | Hospitality | 2018 |
| Blue Scaffolding Ltd | Construction | 2014 |
| Blue Vision Consulting Group LLP | | 2022 |
| Bluebell House Care Limited | Health & social care | 2026 |
| Bluebell Property Solutions Limited | Real estate | 2021 |
| Bluebelle Retail Ltd | Wholesale & retail | 2013 |
| Bluebird International Ltd | Administrative & support | 2026 |
| Bluebrick and Steel Developments Limited | Construction | 2014 |
| Bluebridge Living Ltd | Real estate | 2025 |
| Bluecause Properties Limited | Real estate | 2025 |
| Bluefields Asset Management Ltd | Financial services | 2023 |
| Bluefields Property Portfolio Ltd | Real estate | 2023 |
| Bluehat Cyber Ltd | Information & communication | 2023 |
| Bluehawk Networks & Security Ltd | Construction | 2023 |
| Blueline Group Ltd | Construction | 2025 |