| John Islip Street (Freehold) Limited | Real estate | 2004 |
| John Islip Street (Management) Limited | Households | 1977 |
| John Lyon Properties Limited | Real estate | 2019 |
| John Parry Electrical Limited | Energy | 2016 |
| John R Luck and Company Limited | Construction | 1987 |
| Johnson Elborne Holdings Limited | Financial services | 2023 |
| Johnson Elborne UK Limited | Administrative & support | 2018 |
| Jonathan Dean Developments Limited | Construction | 1972 |
| Jonathan Hilton Consulting Ltd | Professional & scientific | 2025 |
| Jones Property Limited | Real estate | 2019 |
| Jones Realty Limited | Real estate | 2012 |
| Joraz Properties Limited | Real estate | 2014 |
| Jordans Environment Trust Limited | Health & social care | 1973 |
| Jordans Hostel Community Interest Company | Hospitality | 2025 |
| Joseph Avison Consultancy Ltd | Professional & scientific | 2010 |
| Joyful Nails Ltd | Other services | 2021 |
| JP Properties & Management Limited | Real estate | 2001 |
| JPH EOT Ltd | Professional & scientific | 2022 |
| Jrmg Ltd | Financial services | 2025 |
| JS Group Investment Limited | Financial services | 2025 |
| JSG Medicolegal Limited | Health & social care | 2025 |
| JSR Collectables Ltd | Wholesale & retail | 2022 |
| JT Business Growth Limited | Extraterritorial | 2020 |
| JT Capital Growth Limited | Extraterritorial | 2020 |
| JT Exhibition Management LLP | | 2018 |
| Jtmc Productions Ltd | Information & communication | 2021 |
| Jude Street Residents Management Company Limited | Households | 2021 |
| Julia Ross AI Limited | Information & communication | 2025 |
| Julia Ross Group Limited | Construction | 2018 |
| Julian Barrett Limited | Professional & scientific | 2014 |
| Julian Barrett Property Limited | Real estate | 2020 |
| Julian Christopher Developments Limited | Construction | 2008 |
| Junkshon Limited | Information & communication | 2017 |
| Juralex Limited | Professional & scientific | 2014 |
| Jutla Ltd | Construction | 2014 |
| K & B Partnership LLP | | 2025 |
| K D Berkshire 2 Limited | Real estate | 2022 |
| K D Berkshire Limited | Real estate | 2022 |
| K D Bibbsworth Hall Limited | Real estate | 2022 |
| K D Church Road Limited | Financial services | 2022 |
| K D Marlow High Street Limited | Real estate | 2023 |
| K Senior Coaching and Mentoring Ltd | Administrative & support | 2018 |
| K2 Critical Delivery (UK) Ltd. | Professional & scientific | 2017 |
| K4 Creative Holdings Limited | Other services | 2011 |
| KAD2 Group Limited | Real estate | 2025 |
| Kafe 23 Limited | Wholesale & retail | 2015 |
| Kaizen Tech Services Ltd | Information & communication | 2025 |
| Kalaharix Limited | Wholesale & retail | 1998 |
| Kallaway Group Limited | Professional & scientific | 2003 |
| Kalsi Estates Limited | Real estate | 2016 |
| Kamet One Limited | Professional & scientific | 2022 |
| Karlau Limited | Wholesale & retail | 2013 |
| Karma Bay Limited | Wholesale & retail | 2019 |
| Kasemjampee Ltd | Hospitality | 2017 |
| Katie Influence Limited | Arts & recreation | 2025 |
| KB XPS Ltd | Transport & logistics | 2018 |
| KB3130 Limited | Real estate | 2022 |
| Kbpr Limited | Professional & scientific | 2011 |
| Kbsg Stores Limited | Wholesale & retail | 2021 |
| Kbsm Estates Ltd | Real estate | 2025 |
| KD Bibbsworth 1 Limited | Real estate | 2025 |
| KD Bibbsworth 2 Limited | Real estate | 2025 |
| KD Bibbsworth 3 Limited | Real estate | 2025 |
| KD Bibbsworth 4 Limited | Real estate | 2025 |
| KD Bibbsworth 5 Limited | Real estate | 2025 |
| Kearney Services Limited | Professional & scientific | 2020 |
| Kebbell Country Homes Limited | Construction | 2006 |
| Kebbell Development Limited | Construction | 1959 |
| Kebbell Holdings Limited | Professional & scientific | 1963 |
| Kebbson and Co Ltd | Professional & scientific | 2023 |
| Kebric Plant Limited | Real estate | 1957 |
| Keen People Ltd | Information & communication | 2021 |
| Kehar Builders Ltd | Construction | 2006 |
| Kellforms Woodmasters Limited | Real estate | 1964 |
| Kenyon Family Group Ltd | Financial services | 2023 |
| Kenyon Investments Limited | Real estate | 2015 |
| Kersogan Consulting Limited | Professional & scientific | 1998 |
| Kersogan Services Limited | Financial services | 2017 |
| Kevita Limited | Other services | 2022 |
| Key Construction People Ltd | Administrative & support | 2024 |
| Keystone Buildworks Limited | Construction | 2025 |
| Kickboxingsquad CIC | Arts & recreation | 2022 |
| Kika Beauty Limited | Other services | 2026 |
| Kika Beauty Studio Limited | Other services | 2026 |
| Kind Energy Ltd | Construction | 2017 |
| Kingham Green Interiors Ltd | Professional & scientific | 2013 |
| Kingsley Priest Limited | Hospitality | 2008 |
| Kingsmead Road Management Limited | Households | 2009 |
| Kingsway Homes (Berkshire) Limited | Extraterritorial | 2015 |
| Kinnaird Investment Property Limited | Real estate | 2018 |
| Kiran Kaur Properties Ltd | Real estate | 2026 |
| Kirkmore Bromley Limited | Real estate | 2024 |
| Kirkmore Capital 2 Limited | Financial services | 2024 |
| Kirkmore Capital Limited | Financial services | 2016 |
| Kirkmore Finance 1 Limited | Financial services | 2024 |
| Kirkmore HT Limited | Financial services | 2017 |
| Kirkmore MSL Limited | Real estate | 2018 |
| Kirkmore Northaw Limited | Real estate | 2026 |
| Kirkmore Properties Limited | Extraterritorial | 2002 |
| Kirkmore Rhino 1 Limited | Financial services | 2016 |