| Blackfinch Energy Transition Nominees Limited | Cheltenham | 2024 |
| Blackfinch Financial Limited | Cheltenham | 2005 |
| Blackfinch Group Limited | Cheltenham | 2005 |
| Blackfinch Holdings Limited | Cheltenham | 2019 |
| Blackfinch Investments Limited | Cheltenham | 1992 |
| Blackfinch Nominees Limited | Cheltenham | 2013 |
| Blackfinch Spring VCT PLC | Cheltenham | 2019 |
| Blackfinch Trustees Limited | Cheltenham | 2018 |
| Blackfinch Ventures Nominees Limited | Cheltenham | 2018 |
| Blackfire Trading Ltd | Barnet | 2023 |
| Blackfishers Ltd | London | 2018 |
| Blackfoot (Holdings) Ltd | Brighton | 2012 |
| Blackfoot Asset Management Limited | Crowborough | 2020 |
| Blackford Capital Ltd | London | 2026 |
| Blackford Financial Solutions Limited | Blackford | 2007 |
| Blackford Group Limited | Inverness | 2018 |
| Blackford Holdings Ltd | London | 2019 |
| Blackfordby Finance Limited | Blackfordby | 2013 |
| Blackfort Global Ltd | Cheltenham | 2025 |
| Blackfort Group Ltd | London | 2024 |
| Blackfox Partners Ltd | Cardiff | 2025 |
| Blackfriars (West Norfolk) Limited | Norfolk | 1997 |
| Blackfriars Advisors Ltd | London | 2016 |
| Blackfriars Asset Management Limited | London | 1996 |
| Blackfriars Court Limited | King'S Lynn | 2016 |
| Blackfriars Insurance Brokers Limited | Leeds | 1995 |
| Blackfriars Wealth Management Ltd | Gloucester | 2014 |
| Blackgate Holdings North Ltd | Stoke-On-Trent | 2010 |
| Blackgate Investments Ltd | Horsham | 2025 |
| Blackglass Capital Ltd | London | 2025 |
| Blackgold Capital Ltd | London | 2013 |
| Blackgrid Holdings Limited | Bolton | 2025 |
| Blackham Court Holdings Limited | Faversham | 2022 |
| Blackhawk Financial Ltd | London | 2024 |
| Blackhawk Global Capital Ltd | London | 2023 |
| Blackhawk Insurance Services Limited | Westcliff-On-Sea | 2013 |
| Blackheart Holdings Ltd | Stockport | 2026 |
| Blackheath Apex Holding Group Ltd | London | 2026 |
| Blackheath Group Limited | West Midlands | 1933 |
| Blackheath Prop Co Ltd | London | 2026 |
| Blackheath Property Holdings Ltd | Norwich | 2019 |
| Blackhedge Holdings Limited | Ware | 2017 |
| Blackhill Private Finance Limited | London | 2021 |
| Blackhillock Grid Complex Limited | London. | 2021 |
| Blackhorse Capital Group Ltd | Belfast | 2025 |
| Blackhound Investments Limited | Hampshire | 2015 |
| Blackhouse Holdings 1 Limited | London | 2019 |
| Blackhouse Investments Limited | Nr Hulland Ward | 2024 |
| Blackhurst Investments Limited | Macclesfield | 2012 |
| Blackinkgroup Limited | London | 2021 |
| Blackjack Beers (Holdings) Limited | Manchester | 2019 |
| Blackjade Finance Ltd | Belfast | 2024 |
| Blackladies Investments Limited | Brewood | 2019 |
| Blacklands Finance Limited | London | 1991 |
| Blackleaf Financial Planning Ltd | Huddersfield | 2026 |
| Blackledge Mortgage Services Limited | Colne | 2019 |
| Blackler Finance Ltd | London | 2023 |
| Blackline Holdings Limited | Cullompton | 2023 |
| Blacklink Legal Indemnities Ltd | Salford | 2023 |
| Blacklion Capital Group Ltd | Belfast | 2025 |
| Blackmar Limited | West Malling | 2019 |
| Blackmaria Ltd | London | 2017 |
| Blackmarsh Ltd | Sherborne | 2024 |
| Blackmead Forestry II Limited | London | 2021 |
| Blackmead Forestry III Limited | London | 2012 |
| Blackmead Forestry Limited | London | 2020 |
| Blackmead Solar Limited | London | 2023 |
| Blackmere Capital Management Ltd | London | 2025 |
| Blackmere Limited | London | 2025 |
| Blackmont Capital Ltd | London | 2026 |
| Blackmont Strategic Advisory Ltd | Manchester | 2021 |
| Blackmoor Investment Partners Limited | London | 2016 |
| Blackmoor Risk Limited | Worthing | 2026 |
| Blackmore Bond PLC | London | 2016 |
| Blackmore Park Holdings Limited | Worcester | 1992 |
| Blackmoreholdings Limited | London | 2026 |
| Blackmount Capital Ltd | London | 2026 |
| Blackmount Private Wealth Limited | Glasgow | 2022 |
| Blackness Asset Limited | Woking | 2018 |
| Blacknight Capital Limited | Feltham | 2026 |
| Blacknoll Holdings Limited | Dorchester | 2023 |
| Blackoak Capital Partners Limited | Chester | 2021 |
| Blackoak Equity Ltd | London | 2022 |
| Blackoak Intermediate Life Limited | Chester | 2025 |
| Blackoak Life Limited | Chester | 2013 |
| Blackox Ventures Limited | Birmingham | 2021 |
| Blackpearl Finance Ltd | Stanmore | 2025 |
| Blackpebble Ltd | Brighton | 2019 |
| Blackpoint Biotech Limited | London | 2022 |
| Blackpole Group Limited | Kidderminster | 2025 |
| Blackpoll Holdings Limited | Bournemouth | 2021 |
| Blackprint Holdings Ltd | Dudley | 2024 |
| Blackrayder Investments Ltd | London | 2025 |
| Blackridge Capital Partners Ltd | London | 2026 |
| Blackridge Crown Investments Ltd | London | 2024 |
| Blackridge Enterprises Ltd | Belfast | 2025 |
| Blackridge Group Ltd | London | 2025 |
| Blackridge Oxford Ltd | Oxford | 2022 |
| Blackridge Risk Services Ltd | Sutton | 2026 |
| Blackrock Advisors (UK) Limited | London | 1964 |