| Black HAT Ventures Ltd. | Exeter | 2025 |
| Black Hill Holdings Limited | Oldham | 2006 |
| Black Hill Private Office Limited | London | 2025 |
| Black Hollow Group Ltd | Wellington | 2025 |
| Black Horse (TRF) Limited | London | 1999 |
| Black Horse Finance Holdings Limited | | 1999 |
| Black Horse Homes Holding Limited | Birmingham | 2025 |
| Black Horse Limited | | 1960 |
| Black Hydra Investments Limited | Manchester | 2014 |
| Black INK UK Property Ltd | Ryehill | 2020 |
| Black Isle Capital Partners Limited | London | 2022 |
| Black J a Limited | Lincoln | 2023 |
| Black Kettle Group Limited | Harrogate | 1999 |
| Black Kettle International Limited | Harrogate | 1999 |
| Black Key Enterprises Ltd | London | 2025 |
| Black Knight Capital Limited | Manchester | 2026 |
| Black Knight Financial Services Limited | Bedford | 2025 |
| Black Knight Football Club UK Limited | Bournemouth | 2022 |
| Black LAB Investments Limited | Taunton | 2021 |
| Black LAB Norton Ltd | Litlington | 2013 |
| Black Label Financial Ltd | Seaford | 2010 |
| Black Label Holdings Ltd | Lisburn | 2025 |
| Black Label Syndicate Limited | Horsham | 2020 |
| Black Label Wealth Management Ltd | Poole | 2015 |
| Black Lion Broking Services Ltd | Thames Ditton | 2016 |
| Black Lion Wealth Management Limited | Cardiff | 2018 |
| Black Lola Ltd | London | 2019 |
| Black Manga Group Ltd | London | 2025 |
| Black Mango Capital UK Ltd | Birmingham | 2014 |
| Black Manor Limited | Lichfield | 2011 |
| Black Marble Group Ltd | Chelmsford | 2023 |
| Black Maverick Investments Ltd | Pontypridd | 2022 |
| Black Megaurion Ltd | London | 2024 |
| Black Metals Trading Limited | London | 2016 |
| Black Mountain Asset Management Limited | Hereford | 2021 |
| Black Mountain Mortgages Ltd | Swansea | 2025 |
| Black Nose Holdings Ltd | Liverpool | 2026 |
| Black Oak Global Ltd. | London | 2015 |
| Black Oak Holdings Ltd | Coventry | 2025 |
| Black Oak Investment Group Limited | Stanmore | 2020 |
| Black Oaks Investments Limited | Pinner | 2013 |
| Black Onyx Holdings Limited | Stoke-On-Trent | 2020 |
| Black Onyx Investment Group Ltd | Woodford Green | 2025 |
| Black OPS Security Group Ltd | Aylesbury | 2025 |
| Black OPS Security Services Ltd | Essex | 2026 |
| Black ORB Holdings Ltd | London | 2023 |
| Black Orbit Commodity Partners Ltd | Carshalton | 2025 |
| Black Orchid Corporation Ltd | London | 2023 |
| Black OWL Holdco Ltd | London | 2025 |
| Black OWL Ventures Ltd | London | 2025 |
| Black Panther Capital Ltd | Portsmouth | 2019 |
| Black Panther Holdings Ltd | Axminster | 2024 |
| Black Pearl Capital Management Ltd | Bristol | 2019 |
| Black PIG Holdings Limited | Royston | 2021 |
| Black PIG Investments Limited | Weybridge | 2021 |
| Black Point Partnership Limited | London | 2013 |
| Black Point Patrimonial (UK) Ltd | London | 2025 |
| Black Porcelain Investments Ltd | Bristol | 2020 |
| Black Property & Investments Limited | Southampton | 2024 |
| Black Raven Capital Ltd | London | 2020 |
| Black Raven Holdings Ltd | London | 2020 |
| Black Resin Cosmetics Ltd | Kettering | 2026 |
| Black REX Holdings Limited | York | 2026 |
| Black Robin Capital Limited | Penrith | 2024 |
| Black Rock Express Insurance and Financial Services Limited | Tonbridge | 2000 |
| Black Rock Financial Ltd | Romford | 2012 |
| Black Rock Group of Companies Ltd | London | 2025 |
| Black Rock Restaurant Group Ltd | Brighton | 2017 |
| Black ROD Financial Ltd | Wimborne | 2026 |
| Black Rose Group Ltd | London | 2025 |
| Black Rose Holdings Ltd | London | 2018 |
| Black Rosh Ltd | Slough | 2024 |
| Black Sapphire Finance Limited | London | 2017 |
| Black Sea and Baltic General Insurance Company Limited | | 1925 |
| Black Sea Entertainment Ltd | London | 2016 |
| Black Seven Holdings Ltd | Wrexham | 2025 |
| Black Shadow Limited | Kent | 2007 |
| Black Sheep Capital Limited | London | 2017 |
| Black Sheep Financial Ltd | Blackpool | 2017 |
| Black Shield Protection Ltd | Barking | 2025 |
| Black Shield Security Ltd | Bradford | 2025 |
| Black Spring Investments Limited | Llanelli | 2025 |
| Black Springs Investments | Edinburgh | 2023 |
| Black Square Portfolio Ltd | London | 2021 |
| Black Stallion London Limited | London | 2017 |
| Black Star Holdings Limited | London | 2017 |
| Black Stars Investments Limited | London | 2020 |
| Black Stone Capital Investment Limited | London | 2025 |
| Black Stone Commercial Finance Ltd | Swanage | 2019 |
| Black Swan Capital Ltd | Hove | 1999 |
| Black Swan Capital Trading Ltd | London | 2017 |
| Black Swan Currency Ltd | Kingston Upon Thames | 2020 |
| Black Swan Developments Limited | Brightlingsea | 2021 |
| Black Swan Film Group Ltd | Blackwood | 2026 |
| Black Swan Financial Services Ltd | Southampton | 2014 |
| Black Swan Obsidian Ltd | Braintree | 2025 |
| Black Swan Recruitment Limited | London | 2013 |
| Black Swan Tax Limited | Liverpool | 2025 |
| Black Swan Topco Limited | Norwich | 2020 |
| Black Swan UK Holdings Ltd | Southampton | 2019 |