| Birth and Beyond (Bucks) Limited | Health & social care | 2017 |
| Biscuit AV Ltd | Construction | 2018 |
| Bishop's Skip Hire Limited | Water & waste | 1986 |
| BIT and Byte Solutions Limited | Information & communication | 2012 |
| Bittree Digital Limited | Information & communication | 2018 |
| Biz-Tech Communications Limited | Information & communication | 2014 |
| Bizen Solutions Ltd | Transport & logistics | 2026 |
| BJB Management Ltd | Arts & recreation | 2017 |
| Bjic Business Services Limited | Information & communication | 2010 |
| BJL Law Ltd | Professional & scientific | 2024 |
| BJP Property Investments Ltd | Real estate | 2024 |
| BK Arlo Construction Ltd | Construction | 2026 |
| BK Organises for YOU Ltd | Administrative & support | 2025 |
| Bkaur Enterprises Limited | Wholesale & retail | 2020 |
| BKD Admin Services Ltd | Administrative & support | 2025 |
| BL Construction Ltd | Construction | 2025 |
| Black 5 Consultancy Limited | Professional & scientific | 2026 |
| Black Letter PR LLP | | 2011 |
| Black Onyx Partnership Ltd | Administrative & support | 2009 |
| Black Time Film Ltd | Information & communication | 2023 |
| Blackbird Channel Ltd | Information & communication | 2010 |
| Blackcat Networks Ltd | Information & communication | 2021 |
| Blackcurrant Babies Limited | Manufacturing | 2014 |
| Blackcurrant Media Limited | Professional & scientific | 2008 |
| Blackhawk Network Emea Limited | Administrative & support | 2001 |
| Blackness Films Ltd | Information & communication | 2020 |
| Blains Trailers & Tyres Ltd | Wholesale & retail | 1997 |
| Blake Johnson Healthcare Ltd | Health & social care | 2021 |
| Blake's Roofing Specialists Ltd | Other services | 2021 |
| Blakemore Manor (Hertford) Management Company Ltd | Households | 2020 |
| Blaze Peri Peri Burgers Ltd | Hospitality | 2026 |
| Bligh Properties Ltd | Real estate | 2025 |
| Blissreal Experience Ltd | Administrative & support | 2025 |
| Blitas Ltd | Professional & scientific | 2020 |
| Blizzard Telecom Limited | Information & communication | 2007 |
| Blizzard Utilities Limited | Energy | 2006 |
| Blizzard Utility Holdings Limited | Financial services | 2011 |
| Blizzard Utility Trustees Limited | Professional & scientific | 2019 |
| Blizzard Wholesale Limited | Information & communication | 2009 |
| Blockchainten Limited | Professional & scientific | 2018 |
| Bloom & Vine Floral Design Ltd | Wholesale & retail | 2026 |
| Bloom Group Thailand Ltd | Real estate | 2026 |
| Bloom Life Science Ltd | Administrative & support | 2024 |
| Bloomsbury Dental Services Limited | Health & social care | 2017 |
| Bloomsproperty Ltd | Real estate | 2018 |
| Bloq Management Services Limited | Real estate | 2013 |
| Blossom Gate (Congleton) Management Company Limited | Households | 2019 |
| Blsomerset Ltd | Real estate | 2025 |
| Blubell Estates Limited | Real estate | 2022 |
| Blue a Ltd | Water & waste | 2013 |
| Blue Business Capital Ltd | Financial services | 2025 |
| Blue Cloud Property Maintenance Ltd | Construction | 2019 |
| Blue Cloud Property Renovations Ltd | Construction | 2016 |
| Blue Cuckoo Ltd | Other services | 2016 |
| Blue Duck Luck Limited | Information & communication | 2019 |
| Blue Horizon Developers Ltd | Construction | 2025 |
| Blue Light Gift CIC | Wholesale & retail | 2024 |
| Blue Man's Court Management Company Limited | Households | 2002 |
| Blue Nile Consulting Ltd | Professional & scientific | 2013 |
| Blue Scenic Ltd | Construction | 2025 |
| Blue SEO Ltd | Professional & scientific | 2020 |
| Blue Shield Fire Protection Ltd | Construction | 2003 |
| Blue Shield Property Limited | Professional & scientific | 2005 |
| Blue Solar Ltd | Construction | 2025 |
| Bluebell Boutique Limited | Wholesale & retail | 2010 |
| Bluebell Woods (Wyke) Management Company Limited | Households | 2015 |
| Bluebelles by the Sea Ltd | Wholesale & retail | 2021 |
| Blueberry Local Ltd | Wholesale & retail | 2022 |
| Bluedeckshoe Ltd | Information & communication | 2025 |
| Bluehorizonproperty Ltd | Real estate | 2026 |
| Bluesky Support & Cleaning Services Limited | Administrative & support | 2010 |
| Blukloud Ltd | Information & communication | 2021 |
| Blumatech Ltd | Professional & scientific | 2019 |
| Blurok Ltd | Professional & scientific | 2016 |
| Blush & Co (London) Ltd | Other services | 2023 |
| BM World Consulting LLP | | 2025 |
| BMC Bodyshop (Hemel Hempstead) Limited | Wholesale & retail | 2016 |
| BMC Consultancy Limited | Information & communication | 2012 |
| Bmce Networks Limited | Information & communication | 2011 |
| BMH Design Engineers Ltd | Professional & scientific | 2016 |
| BMR Developments Ltd | Construction | 2021 |
| BNH Limited | Construction | 2024 |
| BNM Drylining Ltd | Construction | 2020 |
| Bobby 76 Ltd | Transport & logistics | 2014 |
| Bobby's Driving School Ltd | Education | 2025 |
| Bobson Chifan Ltd | Construction | 2014 |
| Bodis Holdings Ltd | Real estate | 2021 |
| Bodis Media Ltd | Professional & scientific | 2017 |
| Body Unity (Hemel Hempstead) Ltd | Health & social care | 2024 |
| Body Unity Ltd | Health & social care | 2023 |
| Boghani Groups Ltd | Professional & scientific | 2023 |
| Bogjohn Trans Ltd | Wholesale & retail | 2017 |
| Boho 72 Limited | Wholesale & retail | 2020 |
| Bojoaga Ltd | Real estate | 2021 |
| Bola Verde Ltd | Real estate | 2025 |
| Bolag Consulting Ltd | Professional & scientific | 2022 |
| Bold Writers Ltd | Information & communication | 2023 |
| Bollin Meadow Management Company Limited | Real estate | 2017 |
| Bolton Hotel Opco Limited | Financial services | 2025 |
| Bolton Hotel Propco Limited | Financial services | 2025 |