| Jane Baker Education and Skills Limited | Education | 2013 |
| Janey LEE Grace Training Ltd | Education | 2022 |
| Jasmine Thyme Ltd | Wholesale & retail | 2022 |
| Jaycee Contract Flooring Ltd | Construction | 2013 |
| Jerram Carpentry & Construction Ltd | Construction | 2022 |
| JET Events Limited | Other services | 2019 |
| JGC IT Services Limited | Information & communication | 2023 |
| JGE Homes Limited | Real estate | 2022 |
| JHS Supplies Ltd | Professional & scientific | 2021 |
| JJK Fitness Ltd | Arts & recreation | 2017 |
| JJK Fitness Retreats Ltd | Arts & recreation | 2019 |
| JJK Fuel Ltd | Hospitality | 2018 |
| JLR Property Management Ltd | Real estate | 2023 |
| JLS Scaffolding Ltd | Construction | 2015 |
| JMP Traffic Management Ltd | Administrative & support | 2025 |
| JMR Pro Limited | Other services | 2025 |
| John Alexander Homes Limited | Construction | 2024 |
| John E.Fells & Sons Limited | Wholesale & retail | 1920 |
| John James Building Contractors Limited | Construction | 2010 |
| John Wheeler Consulting Limited | Professional & scientific | 2006 |
| Johnson and Butlers Ltd | Wholesale & retail | 2024 |
| JON Hurp Consultancy Limited | Professional & scientific | 2017 |
| Jonameden Ltd | Real estate | 2026 |
| Journeys With Jane Ltd | Health & social care | 2025 |
| Jpmeads Limited | Construction | 2023 |
| JPT Management Services Limited | Professional & scientific | 2020 |
| JRH Delivery Services 1004 Ltd | Transport & logistics | 2025 |
| Juicebox Bars Ltd | Hospitality | 2021 |
| Juicebox Live Development & Training CIC | Arts & recreation | 2020 |
| Juicebox Live Promotions Ltd | Arts & recreation | 2020 |
| Jumby Investments Ltd | Real estate | 2015 |
| Jurassic Productions Ltd | Information & communication | 2023 |
| JUST1ACTION Ltd | Administrative & support | 2022 |
| JZM Limited | Wholesale & retail | 2008 |
| K & B Associates Ltd | Professional & scientific | 2026 |
| K9 Fertility Services Ltd | Professional & scientific | 2021 |
| Kaaliga Limited | Wholesale & retail | 2015 |
| Kadri Zade Limited | Information & communication | 2023 |
| Kaliga & Co Ltd | Wholesale & retail | 2023 |
| Kapitalize LLP | | 2009 |
| Katherine Place Limited | Health & social care | 2023 |
| Kavok Ltd | Extraterritorial | 2014 |
| KAY Nominees Limited | Extraterritorial | 1995 |
| Kaydee Investments Ltd | Construction | 2004 |
| Kbfd Limited | Professional & scientific | 2024 |
| Kd-B Developments Limited | Construction | 2001 |
| KDS Info Limited | Information & communication | 2009 |
| Kedgling Developments Ltd | Real estate | 2015 |
| Keep IT Simple - Business Services Limited | Construction | 2014 |
| Kelly Ventures Limited | Administrative & support | 2021 |
| Kennealy Estates Ltd | Real estate | 2024 |
| Kenwyn Solar Limited | Energy | 2013 |
| Khalif Property Holdings Ltd | Real estate | 2024 |
| KHH Group Ltd | Financial services | 2026 |
| Kiki Corporation Ltd | Wholesale & retail | 2019 |
| Kingley Park Management Company Limited | Households | 2009 |
| Kings House Management (UK) Limited | Real estate | 2007 |
| Kings Langley 4X4 Limited | Wholesale & retail | 2017 |
| Kings Langley Estates Limited | Real estate | 2006 |
| Kings Langley Estates WD4 Ltd | Real estate | 2023 |
| Kings Langley FC Ltd | Arts & recreation | 2016 |
| Kings Langley School | Education | 2012 |
| Kings Mechanical Electrical Ltd | Construction | 2018 |
| Kings Property Developments Limited | Real estate | 2020 |
| Kingston Solar Limited | Energy | 2019 |
| Kingsway Products Limited | Wholesale & retail | 2016 |
| KIT Essentials Ltd | Extraterritorial | 2011 |
| Kitchen Consultants Ltd | Professional & scientific | 2024 |
| Kitchiner Stone Ltd | Education | 2014 |
| Kitkat's Café Ltd | Agriculture & fishing | 2025 |
| KL Herts Spice Ltd | Hospitality | 2024 |
| KL Tandoori Ltd | Hospitality | 2017 |
| KMC Home Improvements Limited | Construction | 2018 |
| Knight Renewables UK Limited | Professional & scientific | 2012 |
| Knott Park One LLP | | 2011 |
| Konsultan Limited | Real estate | 2017 |
| KRW Transportation Limited | Transport & logistics | 2024 |
| KSI Consulting Services Ltd | Professional & scientific | 2021 |
| L & a Exchange Limited | Real estate | 2019 |
| L&L Home Designs Ltd | Wholesale & retail | 2023 |
| L.J. Real Estate Investments Ltd | Real estate | 2021 |
| LA Colomba London Limited | Professional & scientific | 2024 |
| Lady Meadow Road Association Limited | Other services | 1977 |
| Lakeside Energy Storage Limited | Energy | 2017 |
| Langley Advisory Group Ltd | Financial services | 2026 |
| Langley Autocraft Limited | Wholesale & retail | 2003 |
| Langley Fire Protection Limited | Construction | 2026 |
| Langley Grove (Watford) Management Company Limited | Real estate | 2014 |
| Langley Labels Ltd | Manufacturing | 2002 |
| Langley Motoring Group Limited | Wholesale & retail | 2015 |
| Langley Planning & Design Ltd | Professional & scientific | 2018 |
| Langley Planning Ltd | Professional & scientific | 2021 |
| Langley Spice Limited | Hospitality | 2014 |
| Langleybury Fields Limited | Other services | 1994 |
| Lannary Consulting Services Ltd | Administrative & support | 2014 |
| Larganmore Ltd | Real estate | 2022 |
| Lashpoint Limited | Other services | 2017 |
| Lawrence of London (Travel Related Services) Limited | Administrative & support | 1995 |
| LBB Construction Ltd | Administrative & support | 2017 |
| Lcse Ltd | Professional & scientific | 2018 |