| Jencog Services Limited | Health & social care | 2010 |
| Jennifer Effie's Hair Solutions Limited | Other services | 2014 |
| Jenny Motoring World Ltd | Wholesale & retail | 2024 |
| Jess Trading Limited | Real estate | 2013 |
| Jessie Sutton Limited | Health & social care | 2013 |
| JET Travels Limited | Administrative & support | 2015 |
| Jeyrs Ltd | Real estate | 2021 |
| JF Sixteen Homes Ltd | Real estate | 2024 |
| JG Pure Heating Ltd | Construction | 2015 |
| JGX Ltd | Wholesale & retail | 2025 |
| JH1 Maintenance Ltd | Construction | 2025 |
| JIGSAW4U Limited | Health & social care | 2005 |
| Jimmy Autos Limited | Manufacturing | 2023 |
| Jinnac Limited | Wholesale & retail | 2002 |
| Jiya Food Ltd | Hospitality | 2026 |
| JJ Flores Limited | Health & social care | 2012 |
| JJ Retail Hub Limited | Wholesale & retail | 2026 |
| JJO Construction Limited | Construction | 2007 |
| Jjpm ( London ) Ltd | Construction | 2019 |
| Jjpm South Ltd | Construction | 2025 |
| Jjpr Investments Limited | Real estate | 2025 |
| JJU Limited | Information & communication | 2009 |
| JJV Care Limited | Health & social care | 2022 |
| JK Cleans Ltd | Administrative & support | 2025 |
| JK Trade Solutions Ltd | Wholesale & retail | 2021 |
| JK71GROUP Limited | Wholesale & retail | 2025 |
| Jkem Ltd | Construction | 2016 |
| JL Takeaway Restaurant Ltd | Hospitality | 2022 |
| Jl's Drainage Ltd | Water & waste | 2023 |
| JLB Healthcare Limited | Health & social care | 2022 |
| Jlhb Ltd | Households | 2019 |
| JMG Contracts (London) Limited | Construction | 2011 |
| Jmiah 2911 Limited | Administrative & support | 2018 |
| JML London Property Investment Ltd | Real estate | 2019 |
| JML London Property Ltd | Real estate | 2018 |
| JML Polaris Ltd | Professional & scientific | 2025 |
| JN Infinity Limited | Wholesale & retail | 2026 |
| JN Platinum Estates Ltd | Real estate | 2026 |
| Joboat Ltd | Hospitality | 2025 |
| JOE BEL Limited | Real estate | 2025 |
| Joeztech Limited | Information & communication | 2025 |
| John Mckelvie Ltd | Transport & logistics | 2017 |
| John Property UK2025 Ltd | Real estate | 2025 |
| John Sharp (Wire) Limited | Extraterritorial | 1979 |
| John Shaw Lifting & Testing Services Limited | Extraterritorial | 1967 |
| Johnny Plumbing and Heating Ltd | Manufacturing | 2026 |
| Johny B Ltd | Construction | 2021 |
| JON Tyres Limited | Wholesale & retail | 2024 |
| Jona Infrastructure Advisory Ltd | Professional & scientific | 2023 |
| Jonas Woodhead & Sons Limited | Extraterritorial | 1920 |
| Jonas Woodhead (Manchester) Limited | Extraterritorial | 1946 |
| Jonas Woodhead (Ossett) Limited | Extraterritorial | 1947 |
| Jonas Woodhead (Sheffield) Limited | Extraterritorial | 1914 |
| Jonas Woodhead Limited | Extraterritorial | 1932 |
| Jonathan D'Souza-Rauto Consulting Limited | Professional & scientific | 2026 |
| Jorae Limited | Wholesale & retail | 2019 |
| Josan Property Maintenance Ltd | Real estate | 2025 |
| Josbol Limited | Real estate | 2017 |
| Joshi Repair Ltd | Manufacturing | 2024 |
| Joval Multi-Choice Limited | Energy | 2020 |
| Joval Prime Ltd | Wholesale & retail | 2026 |
| Joyclicks Limited | Information & communication | 2020 |
| Joym Backstage Ltd | Information & communication | 2021 |
| JP London Properties Limited | Real estate | 2014 |
| Jpcandyandpop Ltd | Hospitality | 2024 |
| Jpcarco Limited | Wholesale & retail | 2025 |
| Jratnam Ltd | Hospitality | 2021 |
| JRI Cars Ltd | Transport & logistics | 2026 |
| JS Amazing Ltd | Transport & logistics | 2017 |
| JST Photography Limited | Professional & scientific | 2011 |
| Jstory Vison Ltd | Information & communication | 2025 |
| JTA Soft Services Limited | Administrative & support | 2025 |
| Junglespire Ltd | Wholesale & retail | 2025 |
| Jungletradeskum Ltd | Professional & scientific | 2025 |
| JUS "T" Learn (Merton) Ltd | Education | 2021 |
| Just Chris Carpentry Ltd | Construction | 2015 |
| Justice Academy 60 TAG Ltd. | Arts & recreation | 2022 |
| Justyk Ltd | Construction | 2018 |
| Jutts Heating & Electrics Ltd | Construction | 2016 |
| Juwon Ltd | Administrative & support | 2017 |
| JW Beauty LAB Ltd | Wholesale & retail | 2025 |
| JW Transport (UK) Limited | Transport & logistics | 2014 |
| Jzaib Limited | Wholesale & retail | 2025 |
| JZZ UK Ltd | Wholesale & retail | 2022 |
| K & a Food Centre Ltd | Wholesale & retail | 2010 |
| K & R Creative Ltd | Information & communication | 2024 |
| K 2 a Holdings Limited | Hospitality | 2017 |
| K and L Scaffolding Services Ltd | Construction | 2015 |
| K Marsh Group Ltd | Construction | 2021 |
| K Ming Limited | Professional & scientific | 2010 |
| K MYS Cargo-Van Limited | Transport & logistics | 2017 |
| K PAK Limited | Administrative & support | 2002 |
| K PAK Logistic Services Ltd | Transport & logistics | 2023 |
| K T I (UK) Limited | Wholesale & retail | 2011 |
| K Treads Services Ltd | Manufacturing | 2024 |
| K&A Business Solutions Ltd | Administrative & support | 2025 |
| K&J Kris&Jimmy Ltd | Transport & logistics | 2015 |
| K&K 2 Services Ltd | Transport & logistics | 2020 |
| K&Kanev Ltd | Construction | 2020 |
| K&S Comfort Ltd | Transport & logistics | 2023 |