| Bordon Service Station Limited | Wholesale & retail | 1955 |
| Borough Electrical Limited | Construction | 2014 |
| Borras Construction Ltd. | Construction | 1980 |
| Borras Group Holdings Limited | Financial services | 2013 |
| Bosphorus (ST Albans) Ltd | Hospitality | 2019 |
| Bostock Locum Services Ltd | Professional & scientific | 2013 |
| Boston Heat & Power Ltd | Energy | 2022 |
| Boston Limited | Information & communication | 1992 |
| Boston Superstore Limited | Real estate | 2020 |
| BOT Music Ltd | Arts & recreation | 2019 |
| Both Strands Ltd | Professional & scientific | 2023 |
| Bothongo Hygiene Solutions UK Limited | Manufacturing | 2020 |
| Botsedge Technology Private Limited | Information & communication | 2023 |
| Bottom Line Films Limited | Professional & scientific | 2016 |
| Boucetta Ltd | Administrative & support | 2018 |
| Boutique of Dreams Limited | Wholesale & retail | 2016 |
| Bouyage Studio Ltd | Other services | 2022 |
| Bowpoint Limited | Professional & scientific | 2018 |
| Box Sport London Ltd | Arts & recreation | 2018 |
| Boxer Books Limited | Information & communication | 2000 |
| Boxsport Kids Academy Limited | Education | 2024 |
| BP Management Investment Ltd | Professional & scientific | 2017 |
| Brackley Group Ltd | Construction | 2023 |
| Brackley Property Management Ltd | Hospitality | 2025 |
| Brackner Consultancy Services Ltd | Administrative & support | 2017 |
| Bradford Howley (Harpenden) LLP | | 2010 |
| Bradford Howley LLP | | 2009 |
| Braeburn Court Management Ltd | Households | 2019 |
| Braid Maidens Limited | Extraterritorial | 2024 |
| Brainspark Ltd | Information & communication | 2014 |
| Bramall Enterprises Limited | Education | 2015 |
| Brampton Advisory Limited | Professional & scientific | 2025 |
| Brampton Partners Ltd | Professional & scientific | 2013 |
| Brand Infusion LLP | | 2010 |
| Brand Recruitment Limited | Administrative & support | 2005 |
| Brand Talent Ltd | Professional & scientific | 2011 |
| Branding First Limited | Wholesale & retail | 2019 |
| Brandon Aylott Limited | Other services | 2025 |
| Brandon Bay Holdings Limited | Health & social care | 2020 |
| Brandwell Ltd | Professional & scientific | 2011 |
| Branover Sewerage Ltd | Water & waste | 2024 |
| Brantingham Residential Ltd | Real estate | 2024 |
| Brava Lettings and Property Management Ltd | Real estate | 2026 |
| Brave New Pictures Ltd | Information & communication | 2011 |
| Breaconridge | Financial services | 2012 |
| Breaconridge Chalets Limited | Real estate | 2014 |
| Break. Vintage Ltd | Wholesale & retail | 2022 |
| Brenfold Limited | Professional & scientific | 2015 |
| Bretherton Assets Limited | Administrative & support | 2025 |
| Bretherton Estate Limited | Financial services | 2025 |
| Bretherton Law Ltd | Professional & scientific | 2011 |
| Breton Thomas Garden Design Ltd | Administrative & support | 2019 |
| Brewtini Ltd | Manufacturing | 2025 |
| Brian Moody Cleaning Services Ltd | Other services | 2017 |
| Briants of Risborough Limited | Wholesale & retail | 1964 |
| Briar Capital Limited | Financial services | 2025 |
| Brick & Giggle Properties Ltd | Real estate | 2026 |
| Brick Freedom Limited | Information & communication | 2017 |
| Brick Wood Homes Limited | Construction | 2023 |
| Bricket Services Limited | Construction | 2022 |
| Bricket Wood Cleaning Services Ltd | Administrative & support | 2024 |
| Bricket Wood Limited | Real estate | 2013 |
| Bricketwood Practice Limited | Health & social care | 2025 |
| Bricks Property Ltd | Real estate | 2017 |
| Bricks With Purpose Ltd | Real estate | 2024 |
| Bricktraders ST Albans Ltd | Wholesale & retail | 2026 |
| Bridge Brands Ltd | Wholesale & retail | 2024 |
| Bridge Gate Interiors Limited | Other services | 2017 |
| Bridge Street Limited Partnership | | 2024 |
| Bridge-Mountain Consulting Ltd | Information & communication | 2025 |
| Bridgecloud Ltd | Professional & scientific | 2024 |
| Bridgeland Consulting Limited | Professional & scientific | 2021 |
| Bridgeman Kent Limited | Administrative & support | 2022 |
| Bridgepath Ltd | Professional & scientific | 2024 |
| Bridgewater Consulting Limited | Professional & scientific | 2019 |
| Bridgewater Homes Limited | Construction | 2013 |
| Bright Earth Ltd | Professional & scientific | 2017 |
| Bright Future Home Education UK Limited | Extraterritorial | 2025 |
| Bright Lane Limited | Information & communication | 2023 |
| Bright Lights Business Services Ltd | Administrative & support | 2020 |
| Bright Path Studio Ltd | Health & social care | 2026 |
| Brightcrest Energy Ltd | Construction | 2025 |
| Brighter Blue Psychology LLP | | 2024 |
| Brightline Consultancy Limited | Professional & scientific | 2026 |
| Brightlobe Labs Limited | Professional & scientific | 2023 |
| Brightworthy HR Ltd | Professional & scientific | 2025 |
| Britannia Music Shop Limited | Wholesale & retail | 2006 |
| Britannia RE Limited | Construction | 2022 |
| Britannica Education Consultancy Ltd | Education | 2014 |
| British Association for Early Childhood Education(The) | Education | 1945 |
| Broadlake Studios Limited | Information & communication | 2016 |
| Brohms' Whiskey Ltd | Wholesale & retail | 2023 |
| Brompton DCL Ltd | Real estate | 2016 |
| Bronwen Anthony Counselling Limited | Health & social care | 2016 |
| Brook & Brook Limited | Extraterritorial | 2021 |
| Brooke 5 Limited | Real estate | 2019 |
| Brooke Simons Limited | Professional & scientific | 2021 |
| Brooke Williams Limited | Real estate | 2022 |
| Brookfield Care Home Limited | Health & social care | 2006 |
| Brookfield Limited | Households | 2002 |