| Blaze Media Limited | Information & communication | 2019 |
| Blazesafe Solutions Limited | Professional & scientific | 2025 |
| Blazing Knuckles Limited | Arts & recreation | 2025 |
| Blazing Luxe Ltd | Wholesale & retail | 2025 |
| Blck Mamba Ltd | Administrative & support | 2024 |
| Blek White Ltd | Transport & logistics | 2025 |
| Blend IT Hair Ltd | Wholesale & retail | 2025 |
| Blenheim Road Harrow Management Limited | Households | 1985 |
| Blessed Basket Limited | Professional & scientific | 2023 |
| Blessed Crosses Ltd | Wholesale & retail | 2024 |
| Blessed Holy Family Catholic Academy Trust | Education | 2019 |
| Blessed Riya Limited | Health & social care | 2024 |
| Blighty Films Limited | Information & communication | 2014 |
| Blimey Britannia Ltd | Wholesale & retail | 2024 |
| Blind Vision Limited | Administrative & support | 1994 |
| Blink and Think Ltd | Professional & scientific | 2023 |
| Blink Xpress Limited | Wholesale & retail | 2025 |
| Blinket Limited | Wholesale & retail | 2024 |
| Blinking Media Limited | Information & communication | 2018 |
| Blisful Home Supply Limited | Other services | 2025 |
| Bliss Care Ltd | Administrative & support | 2020 |
| Bliss DRY Cleaners Limited | Other services | 2006 |
| Bliss Health and Wellbeing Limited | Other services | 2024 |
| Bliss Infotech Ltd | Information & communication | 2015 |
| BLK and WHT Records Limited | Administrative & support | 2020 |
| Block Group Properties Ltd | Real estate | 2025 |
| Blockrisk Consulting Ltd | Information & communication | 2026 |
| Blocks Online Limited | Information & communication | 2013 |
| Blond Contemporary Limited | Wholesale & retail | 2015 |
| Blood Sisters Limited | Information & communication | 2013 |
| Bloodline Effects Limited | Information & communication | 2020 |
| Bloom Properties Limited | Financial services | 2017 |
| Bloom Restaurant Limited | Hospitality | 2017 |
| Bloomco Ltd | Professional & scientific | 2014 |
| Bloomesupplements Ltd | Wholesale & retail | 2026 |
| Blooming Boutique Limited | Wholesale & retail | 2013 |
| Bloomsbury Beauty & Aesthetics Ltd | Other services | 2026 |
| Bloomsbury Events Limited | Other services | 2022 |
| Bloomstyle Ltd | Information & communication | 2024 |
| Bloon Box Ltd | Wholesale & retail | 2020 |
| Blossom Education Ltd | Education | 2020 |
| Blossoming Mind Ltd | Education | 2016 |
| Blossoms Care Group Ltd | Health & social care | 2024 |
| Blpv Holdings Ltd | Financial services | 2023 |
| Blrn (Holdings) Ltd | Real estate | 2018 |
| Blrn (London) Ltd | Real estate | 2018 |
| Blrn (West Hampstead) Ltd | Real estate | 2018 |
| BLS Design Limited | Construction | 2019 |
| Bluberry Ltd | Administrative & support | 2024 |
| Blue 7 Enterprises Ltd | Information & communication | 2015 |
| Blue Ace Trading Limited | Wholesale & retail | 2016 |
| Blue Addiction Group Ltd | Administrative & support | 2017 |
| Blue Anchor International UK Limited | Transport & logistics | 2025 |
| Blue Badge Alliance Ltd | Health & social care | 2025 |
| Blue Bay 21 Ltd | Health & social care | 2022 |
| Blue BEE Enterprise Limited | Professional & scientific | 2023 |
| Blue Bird Healthcare Ltd | Health & social care | 2018 |
| Blue Blood Entertainment Limited | Information & communication | 2017 |
| Blue Cactus Ltd | Administrative & support | 2020 |
| Blue Clean Limited | Construction | 2018 |
| Blue Cuckoo Pictures Limited | Information & communication | 2025 |
| Blue Dawn Associates Ltd | Information & communication | 2015 |
| Blue Derm Limited | Health & social care | 2023 |
| Blue Dips Ltd | Arts & recreation | 2017 |
| Blue Dream Marine Limited | Administrative & support | 2007 |
| Blue Electrical Services Limited | Construction | 2007 |
| Blue Funnel Logistics Ltd | Transport & logistics | 2020 |
| Blue Hackle Limited | Administrative & support | 2004 |
| Blue Haven Properties Ltd | Real estate | 2020 |
| Blue Heron Catering Limited | Hospitality | 2012 |
| Blue Horizons Development Limited | Real estate | 2024 |
| Blue Iceberg Limited | Hospitality | 2017 |
| Blue India Properties Limited | Real estate | 2025 |
| Blue Jasmine Property Limited | Real estate | 2022 |
| Blue JAY Consulting Ltd | Information & communication | 2026 |
| Blue Lake Film Limited | Information & communication | 2021 |
| Blue Line Express Haulage Ltd | Transport & logistics | 2026 |
| Blue Lion Place Freehold Limited | Households | 2013 |
| Blue Marlin Television Limited | Information & communication | 2006 |
| Blue Monday Limited | Administrative & support | 2002 |
| Blue Nest Montessori School Ltd | Administrative & support | 2020 |
| Blue Ocean Consultants Ltd | Information & communication | 2018 |
| Blue Ocean Estates Ltd | Real estate | 2022 |
| Blue Ocean Property Consultants Limited | Real estate | 2002 |
| Blue Point (Harrow) Residents Association Ltd | Households | 2002 |
| Blue Point (Tenants) Limited | Households | 2001 |
| Blue Quartz Ltd | Health & social care | 2022 |
| Blue Season Limited | Professional & scientific | 2024 |
| Blue Sky Builders Ltd | Construction | 2017 |
| Blue Sky Corporate Solutions Limited | Professional & scientific | 2008 |
| Blue Sky Fostering Limited | Health & social care | 2005 |
| Blue Sonic (Europe) Limited | Wholesale & retail | 2016 |
| Blue Square Motors Ltd | Wholesale & retail | 2018 |
| Blue Square Property Solutions Ltd | Real estate | 2023 |
| Blue Star Dent Limited | Health & social care | 2022 |
| Blue Theobald Limited | Information & communication | 2005 |
| Blue Thread Solutions Limited | Information & communication | 2010 |
| Blue Tornado Limited | Wholesale & retail | 1996 |
| Blue Umbrella Films Ltd | Information & communication | 2026 |
| Blue Universe Ltd | Professional & scientific | 2021 |