| Jackson House RTM Company Limited | Households | 2005 |
| Jade-Aden Interiors Holdings Ltd | Financial services | 2026 |
| Jade-Aden Interiors Ltd | Construction | 2014 |
| Jadlam Ltd | Real estate | 2024 |
| Jaluch International Ltd | Education | 2002 |
| Jaluch Limited | Administrative & support | 2002 |
| JAM Technologies Limited | Information & communication | 2018 |
| James Cromwell Ltd | Wholesale & retail | 2017 |
| James Dean Plumbing & Heating Ltd | Construction | 2023 |
| Jamie Mccall Electrical & AV Solutions Limited | Construction | 2015 |
| Janeyco Ltd | Real estate | 2021 |
| Janine Bristow Design Limited | Professional & scientific | 2021 |
| Janist Associates Limited | Education | 2016 |
| Jayar Construction Ltd | Construction | 2025 |
| Jayar Developments Ltd | Construction | 2025 |
| JBK Medical Limited | Health & social care | 2013 |
| JBP Electrical Contractors Ltd | Construction | 2019 |
| JDL Painting Services Ltd | Construction | 2024 |
| Jerry Curtin Limited | Manufacturing | 2002 |
| Jessops Transport Ltd | Transport & logistics | 2019 |
| Jetak Consulting Ltd | Professional & scientific | 2019 |
| Jharrold Limited | Wholesale & retail | 2025 |
| Jhpc Holdings Limited | Health & social care | 2024 |
| Jillian Ltd | Health & social care | 2018 |
| Jiomty's Group Ltd | Real estate | 2019 |
| Jiomtys Auto Centres Ltd | Wholesale & retail | 2019 |
| JJ Drainage Ltd | Water & waste | 2024 |
| JJ Goodman Ltd | Hospitality | 2008 |
| JLM Urology Limited | Health & social care | 2020 |
| Jltp Ltd | Financial services | 2024 |
| Jmdb Properties Limited | Real estate | 2015 |
| JMH Motorsport Limited | Arts & recreation | 2016 |
| JMZ Hospitality & Consultancy Services Ltd | Professional & scientific | 2026 |
| JNB Marketing Ltd | Professional & scientific | 2025 |
| JND Construction & Drainage Ltd | Water & waste | 2025 |
| John Allen & Sons (Oxford) Ltd | Professional & scientific | 2021 |
| Joli Vyann | Arts & recreation | 2018 |
| Jolly Drover Ltd | Hospitality | 2021 |
| JON Parry Building Ltd | Construction | 2018 |
| Jonathan Hannam Ltd | Education | 2014 |
| Jordan Motor H Ltd | Wholesale & retail | 2019 |
| Joymont Legal Ltd | Professional & scientific | 2024 |
| Jpcd Engineering Limited | Professional & scientific | 2019 |
| Jpsh Consultants Limited | Professional & scientific | 2023 |
| JS Training & Consultancy Ltd | Information & communication | 2015 |
| JSB Group UK Ltd | Construction | 2009 |
| JT Paint Prep Services Ltd | Other services | 2019 |
| JT Sailing Ltd | Arts & recreation | 2022 |
| JTW Contractors Limited | Construction | 2006 |
| Julia Allnutt Ltd | Professional & scientific | 2017 |
| Jusan Ltd | Professional & scientific | 2020 |
| Just Fencing Limited | Administrative & support | 2014 |
| Just Right Builders Limited | Information & communication | 2016 |
| Justbright Ltd | Information & communication | 2005 |
| Justin Scriven Physiotherapy Ltd | Health & social care | 2016 |
| JWH Consulting Ltd | Professional & scientific | 2025 |
| Jwpr Enterprises Ltd | Wholesale & retail | 2021 |
| Jwright Garden Maintenance Ltd | Administrative & support | 2025 |
| K a Consultancy Ltd | Information & communication | 1999 |
| K R Carpentry & Construction Ltd | Construction | 2017 |
| K.T.O. Ltd | Arts & recreation | 2013 |
| K5 Property Group Ltd | Construction | 2023 |
| K5 Rental Property Ltd | Real estate | 2025 |
| K60 Development Limited | Construction | 2016 |
| Kairosworks Ltd | Education | 2025 |
| Kamkorp Limited | Professional & scientific | 1990 |
| Kamm (Holdings) Limited | Administrative & support | 2009 |
| Kamm Civil Engineering Limited | Construction | 1995 |
| Kamm Plant Hire LLP | | 2024 |
| Kanye Consultancy Ltd | Manufacturing | 2021 |
| Kapstar Limited | Professional & scientific | 2017 |
| Karkings Ltd | Wholesale & retail | 2018 |
| Karl Simons Consulting Ltd | Health & social care | 2022 |
| Karnilian UK Ltd | Information & communication | 2024 |
| Karuna Living Limited | Health & social care | 2019 |
| Kaya Responsible Travel Ltd | Administrative & support | 2009 |
| KD Accountancy Services Ltd | Professional & scientific | 2021 |
| Keep + Kind Ltd | Wholesale & retail | 2019 |
| Kelleher Group Limited | Construction | 2015 |
| Kennard Mechanical Ltd | Construction | 2021 |
| Key Tiles Limited | Construction | 2022 |
| Keystone Automotive Ltd | Wholesale & retail | 2025 |
| Kieran Humphrey Projects and Advisory Limited | Other services | 2025 |
| Kieran Lees Electrical Ltd | Construction | 2016 |
| Kinetic Sound and Coffee Limited | Wholesale & retail | 2022 |
| King Ventures Limited | Financial services | 2024 |
| Kingfisher Book-Keeping Services Limited | Professional & scientific | 2002 |
| Kingfisher Lake Management Limited | Other services | 2007 |
| Kingfisher Lakes (1987) Ltd | Other services | 1972 |
| Kingsbury Kitchens Limited | Administrative & support | 2017 |
| Kingsfield (Ringwood) Limited | Real estate | 2008 |
| Kingsman Glazing Ltd | Construction | 2019 |
| Kirkbrook Limited | Professional & scientific | 2023 |
| Kitlu Limited | Hospitality | 2014 |
| KJC Consultants Ltd | Administrative & support | 2013 |
| Klopa Ltd | Information & communication | 2025 |
| KM Emerald Estates Ltd | Real estate | 2018 |
| Knights Brown Group Holdings Limited | Financial services | 2024 |
| Knights Brown Group Ltd | Professional & scientific | 2010 |
| Knights Brown UK Ltd | Professional & scientific | 2016 |