| Jennings Racing Limited | Arts & recreation | 2006 |
| Jenningsbet Online Limited | Arts & recreation | 2012 |
| Jewellery Portfolio Limited | Manufacturing | 2002 |
| Jezabelles Ltd | Wholesale & retail | 2025 |
| Jfwp Limited | Real estate | 1957 |
| JH Digital Ltd | Information & communication | 2015 |
| Jigsaw Money Ltd | Financial services | 2017 |
| Jimmy's Mobile Ltd | Other services | 2017 |
| JJS Holdings Group Limited | Hospitality | 2026 |
| JJS M Services Ltd | Construction | 2022 |
| JJS Mechanical Services Ltd | Construction | 2016 |
| JK Healthcare Limited | Health & social care | 2007 |
| JK Sports Cars Ltd | Manufacturing | 2017 |
| Jklm Trading Limited | Information & communication | 2022 |
| JL Bloom Ltd | Construction | 2024 |
| JM10 Football Ltd | Professional & scientific | 2025 |
| JMD Mortgages Limited | Financial services | 2017 |
| JMH Plumbing Heating Building Limited | Construction | 2026 |
| Jmps London Ltd | Administrative & support | 2024 |
| JO Motors London Ltd | Wholesale & retail | 2025 |
| Jobber Projects Limited | Construction | 2004 |
| Jody Nicholls Limited | Construction | 2015 |
| JOE Jennings Bookmakers Limited | Arts & recreation | 2006 |
| John Patient Limited | Construction | 2002 |
| John Pollock (Outfitters) Limited | Administrative & support | 1954 |
| John Ramsey & Sons Limited | Construction | 2005 |
| Jonen Holdings Limited | Financial services | 1972 |
| Jonen Limited | Real estate | 2026 |
| Jopo Marquees Ltd | Arts & recreation | 2025 |
| Jovik Group Limited | Real estate | 2026 |
| Joy Construction Ltd | Construction | 2022 |
| Joy Estates Ltd | Real estate | 2018 |
| JQH Consulting Ltd | Professional & scientific | 2013 |
| JRG Construction Group Limited | Construction | 2018 |
| Jrkr INV Ltd | Financial services | 2025 |
| JSE Associates Limited | Administrative & support | 2010 |
| JTF Technical Services Ltd | Information & communication | 2021 |
| Judejames Group Limited | Hospitality | 2020 |
| Juice Box Mgmt Ltd | Professional & scientific | 2025 |
| K&S Fuels Limited | Wholesale & retail | 2013 |
| Kairo Consulting Limited | Administrative & support | 2026 |
| Kambana Limited | Real estate | 2008 |
| Kaplan Events Ltd | Hospitality | 2026 |
| KAR 7 Limited | Real estate | 2014 |
| Kartec Repair and Refinishers Ltd | Wholesale & retail | 2017 |
| Kashin LLP | | 2022 |
| Kashin PL Ltd | Real estate | 2025 |
| Kashin Property Limited | Real estate | 2016 |
| Katalyst Healthcare Limited | Professional & scientific | 2007 |
| Kate Douglas Ltd | Professional & scientific | 2016 |
| Kawasaki Disease UK Limited | Health & social care | 2018 |
| Kayson Holdings Limited | Financial services | 2021 |
| KDK Foods Limited | Wholesale & retail | 2021 |
| KEE BEE Properties Limited | Real estate | 1993 |
| Keeble's Services Ltd | Wholesale & retail | 2024 |
| Keep ME Promotions Limited | Administrative & support | 2004 |
| Keepme Lifestyle Limited | Wholesale & retail | 2019 |
| Keklik Estates Limited | Real estate | 2025 |
| KEMOSABE35 Limited | Professional & scientific | 2025 |
| Kemrose Ltd | Wholesale & retail | 2025 |
| Keneal Limited | Health & social care | 2015 |
| Keshav Estates Ltd | Real estate | 2021 |
| Kevin Damps Ltd | Manufacturing | 2025 |
| Kevin Pack Financial Consultants Limited | Financial services | 1998 |
| Keylight Electrical Limited | Construction | 2023 |
| Khollis Holdings Limited | Hospitality | 2025 |
| KHU KHU Limited | Manufacturing | 2013 |
| Kids Active Media Ltd | Information & communication | 2010 |
| Kids Active Theatre Company Limited | Administrative & support | 2019 |
| Kinetic Core Group Ltd | Construction | 2025 |
| King Charles Foods Limited | Professional & scientific | 1953 |
| Kings of Essex Limited | Construction | 2012 |
| Kings Properties Limited | Real estate | 2002 |
| Kings Transport Holdings Limited | Financial services | 2024 |
| Kingsbury Airspace Limited | Construction | 2023 |
| Kingsnorth Services Ltd | Information & communication | 2026 |
| Kingswood Cleaning Ltd | Wholesale & retail | 2017 |
| Kiwiworks Limited | Construction | 2023 |
| KJ DOT XYZ Limited | Professional & scientific | 2025 |
| Kjsmiles Limited | Health & social care | 2024 |
| KJV Transport Ltd | Transport & logistics | 2025 |
| Klix Global.Net Limited | Financial services | 2024 |
| Kluge and Kluge LLP | | 2016 |
| Kmart Groceries Ltd | Wholesale & retail | 2025 |
| KMM Management Limited | Manufacturing | 2010 |
| Knightlighting Limited | Information & communication | 2001 |
| Knightylighting Limited | Information & communication | 2025 |
| KNN Futures Limited | Administrative & support | 2003 |
| Knncoborn LLP | | 2009 |
| Kobelt Ltd | Other services | 2016 |
| KP Harlow Limited | Real estate | 2020 |
| KRJ Interiors Ltd | Construction | 2014 |
| Krogulska Ltd | Health & social care | 2024 |
| KS Studio Design Ltd | Professional & scientific | 2025 |
| KSC Broadcast Limited | Professional & scientific | 2010 |
| KSC Technology Ltd | Professional & scientific | 2018 |
| KUL Flavours Ltd | Hospitality | 2025 |
| Kutchenhaus Epping Ltd | Wholesale & retail | 2023 |
| L H Painting Ltd | Construction | 2018 |
| L&C Designs Limited | Administrative & support | 2017 |