| Big Commercial Assets Limited | Financial services | 2023 |
| Big Fish Advantage Limited | Arts & recreation | 2025 |
| Big Power Services LLP | | 2016 |
| Big Shopper Ltd | Wholesale & retail | 2025 |
| Big Shot Management Ltd | Information & communication | 2021 |
| Bigfem IT & Business Management Limited | Public administration | 2025 |
| Bikes for Good Causes Limited | Wholesale & retail | 2014 |
| Bill Bright Limited | Construction | 2004 |
| Bill's Wheels Ltd | Wholesale & retail | 2025 |
| Billericay Farm Services Limited | Manufacturing | 1948 |
| Bimadeb Global Services Limited | Professional & scientific | 2020 |
| Bimprex Ltd | Health & social care | 2018 |
| Bined Ltd | Health & social care | 2022 |
| Bini Ltd | Other services | 2012 |
| Binnit Ltd | Water & waste | 2023 |
| Bino Solutions Ltd | Wholesale & retail | 2022 |
| Biodiscovery Consulting Ltd | Professional & scientific | 2024 |
| Bioinform Ltd | Information & communication | 2010 |
| Bioreg Life Sciences Ltd | Professional & scientific | 2025 |
| Birch Capital Limited | Professional & scientific | 2020 |
| Bird in Hand Court RTM Company Limited | Households | 2021 |
| Bishop & Reed Construction Ltd | Construction | 2016 |
| Bisma Ltd | Wholesale & retail | 2024 |
| Bismot Cleaning Services Ltd | Administrative & support | 2025 |
| Biss One Ltd | Transport & logistics | 2023 |
| BIT4YOU Limited | Transport & logistics | 2024 |
| Bits UK Limited | Information & communication | 1998 |
| Bittany Ltd | Wholesale & retail | 2022 |
| Biya Foods Ltd | Hospitality | 2023 |
| BIZ Projx Ltd | Professional & scientific | 2018 |
| Biztech IT Solutions Ltd | Information & communication | 2013 |
| BJ Carpentry Ltd | Manufacturing | 2025 |
| BJF Building Services Limited | Construction | 2013 |
| BJJ Havering Limited | Arts & recreation | 2016 |
| BK Harlow Limited | Hospitality | 2025 |
| BKV 2003 Ltd | Construction | 2018 |
| Black Bean Productions Ltd | Manufacturing | 2022 |
| Black Book Properties Limited | Real estate | 2025 |
| Black Bull Services Ltd | Wholesale & retail | 2016 |
| Black Eats Ltd | Hospitality | 2020 |
| Black Label Electrical Ltd | Construction | 2018 |
| Black Lion CS Ltd | Professional & scientific | 2024 |
| Black Lion Projects Ltd | Construction | 2025 |
| Black Oak ARB Ltd | Administrative & support | 2023 |
| Black Opal Holdings Ltd | Administrative & support | 2023 |
| Black WAX Music Ltd | Arts & recreation | 2018 |
| Blackbeard Tactical Ltd | Wholesale & retail | 2026 |
| Blackbird Car Maintenance Limited | Wholesale & retail | 2010 |
| Blackhorse Gate Limited | Administrative & support | 2022 |
| Blackman's Building Services Ltd | Construction | 2023 |
| Blackwater LEE Property Management Limited | Households | 2004 |
| Blackwood Property Management Limited | Wholesale & retail | 2023 |
| Blade Court Residents Association Limited | Households | 2004 |
| Blanche Health UK Limited | Health & social care | 2020 |
| Blancmange Co. Ltd | Real estate | 2024 |
| Blanden Property Solutions Ltd | Construction | 2025 |
| Blazersriders Limited | Other services | 2025 |
| Blazin Squad Ltd | Arts & recreation | 2024 |
| BLB Harlow Ltd | Hospitality | 2021 |
| BLD Security Systems Ltd | Administrative & support | 2019 |
| Blessed Dwom Ventures Ltd | Wholesale & retail | 2025 |
| BLG Drylining Ltd | Construction | 2024 |
| Bliss Essentials Limited | Wholesale & retail | 2025 |
| Blissapparel Ltd | Wholesale & retail | 2025 |
| BLK Building Services Limited | Construction | 2023 |
| Blockheads Limited | Arts & recreation | 2001 |
| Bloom and Mellow Tech Services Ltd | Information & communication | 2015 |
| Bloom Consults Limited | Professional & scientific | 2017 |
| Blooming Field Ltd | Real estate | 2024 |
| Blooms Consult Limited | Information & communication | 2023 |
| Blossom and Grow Florist Ltd | Wholesale & retail | 2021 |
| Blossom Healthcare Group Limited | Financial services | 2020 |
| Blossom Healthcare Solutions Hertfordshire Limited | Health & social care | 2020 |
| Blossom Healthcare Solutions Limited | Health & social care | 2019 |
| Blossom Nail Salon Ltd | Other services | 2026 |
| Blossomed Travel and Security Services Ltd | Transport & logistics | 2026 |
| Blossoms Community Nursery Ltd | Education | 2025 |
| Blossoms Nursery Ltd | Education | 2011 |
| Blox Project Management Ltd | Professional & scientific | 2019 |
| Bludor Ltd | Wholesale & retail | 2022 |
| Blue Buddleia Ltd | Extraterritorial | 2025 |
| Blue Coat Court Management Company Limited | Households | 2004 |
| Blue Haven Transport Limited | Transport & logistics | 2021 |
| Blue JAY Consult Ltd | Professional & scientific | 2021 |
| Blue LEE Consulting Ltd | Professional & scientific | 2017 |
| Blue Moon Wealth Ltd | Financial services | 2022 |
| Blue Pearl Homecare Ltd | Health & social care | 2019 |
| Blue Property Management Services Ltd | Real estate | 2021 |
| Blue Sky 20 Ltd | Transport & logistics | 2020 |
| Blue Squirrel Services Ltd | Construction | 2017 |
| Bluebridge Holdings Limited | Professional & scientific | 2007 |
| Bluecrest Property Holding Ltd | Real estate | 2024 |
| Bluedove Care Ltd | Health & social care | 2024 |
| Bluestar Print Finishers Limited | Manufacturing | 2006 |
| Bluestone Conveyancing Services Limited | Professional & scientific | 2025 |
| Bluhill Consulting Ltd | Wholesale & retail | 2013 |
| Blupanda Health Ltd | Health & social care | 2024 |
| Bluz Rock Limited | Hospitality | 2024 |
| Bmat Education | Education | 2011 |
| Bmbh Holdings Ltd | Information & communication | 2021 |