| JS Daniels Consultancy Limited | Administrative & support | 2009 |
| JS Electrical Contractors Ltd | Construction | 2018 |
| JS Hartley Ltd | Health & social care | 2020 |
| JSM Bidco Limited | Financial services | 2020 |
| JSM Construction Limited | Construction | 2023 |
| JSM Group Holdings Limited | Financial services | 2015 |
| JSM Group Services Acquisition Limited | Financial services | 2024 |
| JSM Group Services Holdings Limited | Financial services | 2024 |
| JSM Group Services Intermediate Limited | Financial services | 2024 |
| JSM Group Services Limited | Construction | 1998 |
| JSM Midco Limited | Financial services | 2020 |
| JSM Topco Limited | Financial services | 2020 |
| JTA Developments Ltd | Financial services | 2025 |
| JTC Music Productions Ltd | Arts & recreation | 2012 |
| JTH Group Ltd | Information & communication | 2024 |
| JTJ Art Limited | Information & communication | 2025 |
| Juanxu Consultancy Service Limited | Administrative & support | 2018 |
| Judaicart Publishing Limited | Other services | 2019 |
| Judges Trading Limited | Hospitality | 2020 |
| Judo for ALL UK | Arts & recreation | 2010 |
| Juji Matcha Ltd | Wholesale & retail | 2024 |
| Jujumi Productions Limited Liability Partnership | | 2009 |
| Juliano Transport Ltd | Wholesale & retail | 2018 |
| Jumati Ltd | Hospitality | 2020 |
| Jump Design & Direction Limited | Information & communication | 1996 |
| Junction Internet Limited | Information & communication | 2022 |
| Junction Logistics LLP | | 2018 |
| Jungian Analyst London Ltd | Health & social care | 2022 |
| Jungian Directory CIC | Information & communication | 2022 |
| Junk Daddy Ltd | Water & waste | 2025 |
| Just Gents (Potters Bar) Limited | Other services | 2010 |
| Just Saying Events Limited | Arts & recreation | 2015 |
| Just Seventy Agency Limited | Other services | 2018 |
| Justmill Limited | Real estate | 1985 |
| JWD Health Limited | Other services | 2026 |
| Jyoti Investments Ltd | Real estate | 2017 |
| K C Hunt Ltd | Wholesale & retail | 2022 |
| K C Smith Ortho Limited | Extraterritorial | 2005 |
| K F Global Limited | Extraterritorial | 2013 |
| K George House Management Limited | Real estate | 2024 |
| K Hurst Consulting Limited | Administrative & support | 2026 |
| K Line Properties Ltd | Administrative & support | 2018 |
| K Simmonett Ltd | Other services | 2016 |
| K Squared Consulting Ltd | Professional & scientific | 2021 |
| K&N Associates Limited | Information & communication | 2019 |
| K- MAX Ltd | Wholesale & retail | 1995 |
| K. Achillea Autobody & Paint Limited | Wholesale & retail | 2005 |
| K.D.R. Carpentry & Joinery Ltd | Construction | 2008 |
| K.S. Car Electrics Limited | Real estate | 1973 |
| K2 Material Supply Limited | Wholesale & retail | 2017 |
| K2 Security Services Ltd | Other services | 2017 |
| Kallis London Ltd | Construction | 2024 |
| Kalm Technology Ltd | Wholesale & retail | 2015 |
| Kamalun Ltd | Transport & logistics | 2025 |
| KAN97 Ltd | Wholesale & retail | 2023 |
| Kapacity Plus Ltd | Wholesale & retail | 2021 |
| Kara Properties (UK) Limited | Real estate | 2005 |
| Karlton & Gerd Ltd | Information & communication | 2016 |
| Karma Kreations Limited | Professional & scientific | 2003 |
| Karmma Records Ltd | Wholesale & retail | 2025 |
| Kars Prestige Valeting Limited | Other services | 2010 |
| Kassim Investments 2024 Ltd | Real estate | 2024 |
| Kate Cary Limited | Arts & recreation | 2012 |
| Kavpar Limited | Health & social care | 2021 |
| Kaynath Consultancy Limited | Professional & scientific | 2015 |
| KC Issac Trading Limited | Wholesale & retail | 2025 |
| Kehoewalsh Limited | Professional & scientific | 2015 |
| Keith Rafferty Electrical Limited | Information & communication | 2015 |
| Kell’S Kitchen Limited | Hospitality | 2022 |
| KEM Grab Services Limited | Water & waste | 2020 |
| KEN Building Services Ltd | Construction | 2025 |
| Kenorp Ltd | Real estate | 2025 |
| KER Group Ltd | Information & communication | 2015 |
| Kerntrad Limited | Wholesale & retail | 2019 |
| KES Recovery Ltd | Transport & logistics | 2024 |
| Key Internet Limited | Information & communication | 2020 |
| Keystone Property Maintenance London Ltd | Construction | 2025 |
| Khan's IT Ltd | Information & communication | 2019 |
| Kids, Teens and Adults Limited | Extraterritorial | 2012 |
| Kieanit Properties Limited | Real estate | 2021 |
| Kieanit Tech Limited | Information & communication | 2024 |
| Kielty & Co Ltd | Construction | 2014 |
| Kieran Mccready Ltd | Administrative & support | 2023 |
| Kikka Marco Ltd | Administrative & support | 2016 |
| Kilbey Heating and Plumbing Services Limited | Construction | 2026 |
| Kilikita Transport Limited | Transport & logistics | 2019 |
| Kiltsandkente Limited | Administrative & support | 2024 |
| Kinay Limited | Transport & logistics | 2003 |
| King's Cross Hotel (London) Limited | Hospitality | 2011 |
| King's Road Auction House Ltd | Wholesale & retail | 2025 |
| Kingdom Group Construction Limited | Professional & scientific | 2021 |
| Kingdom Personnel (UK) Limited | Health & social care | 2012 |
| Kings Lodge (Finchley) RTM Company Limited | Real estate | 2013 |
| Kingsley Housing Development Limited | Construction | 2022 |
| Kingsley Housing Limited | Real estate | 2020 |
| Kingsley Housing Property Management Limited | Real estate | 2020 |
| Kingsley Property Group Limited | Real estate | 2018 |
| Kingston 3 Ltd | Real estate | 2018 |
| Kingston Academy Limited | Education | 2021 |
| Kingston Trampoline Academy Limited | Arts & recreation | 2011 |