| Just Imagine Nurseries - Wickford Ltd | Health & social care | 2017 |
| JV Cars Ltd | Wholesale & retail | 2025 |
| Jvsm Properties Ltd | Real estate | 2017 |
| JWG Properties Ltd | Real estate | 2020 |
| K Cordes Building Services Ltd | Construction | 2014 |
| K Macleod Trading Ltd | Financial services | 2019 |
| K Shah Trading Limited | Wholesale & retail | 2020 |
| K&C Consultancy Ltd | Information & communication | 2026 |
| K&K Homecare Ltd | Health & social care | 2013 |
| K&W Industries Ltd | Administrative & support | 2024 |
| K1 Online Services Ltd | Financial services | 2021 |
| Kaban & Company Ltd | Professional & scientific | 2007 |
| Kalibri Limited | Wholesale & retail | 2021 |
| Kalma Film Transport Ltd | Transport & logistics | 2019 |
| Kane International Limited | Manufacturing | 1981 |
| Karpas Engineering Ltd | Professional & scientific | 2018 |
| Karuna Productions Ltd | Information & communication | 2025 |
| Kathirachi Dwellings Ltd | Real estate | 2026 |
| KBL Trading Limited | Other services | 2024 |
| KBN Utilities Ltd | Construction | 2024 |
| Keltech Systems Ltd | Administrative & support | 2016 |
| Kemble Care Homes Limited | Professional & scientific | 2008 |
| Kenmore Property Services Limited | Construction | 2006 |
| Kente Club Ltd | Arts & recreation | 2022 |
| Kente's Spices & Lounge Limited | Hospitality | 2024 |
| Kernival Ltd | Information & communication | 2006 |
| Kevron UK Ltd | Professional & scientific | 2024 |
| Key Stage Locations Ltd | Administrative & support | 2018 |
| Key to Freedom Limited | Real estate | 2017 |
| Keylakes Marketing Limited | Professional & scientific | 2019 |
| KG Elite Properties Limited | Real estate | 2026 |
| KGM Accountancy Ltd | Professional & scientific | 2023 |
| Khelclub Ltd | Administrative & support | 2026 |
| Khen Property Investments Ltd | Real estate | 2026 |
| Kian Dynamics Ltd | Manufacturing | 2026 |
| Kicksncoffee Limited | Other services | 2023 |
| Kiddie Cove Nurseries Limited | Education | 2015 |
| Kids Play Childcare Limited | Health & social care | 2017 |
| Kids Play Ltd. | Education | 1999 |
| Kik-Back Ltd | Education | 2021 |
| Kimshrul Limited | Professional & scientific | 2026 |
| Kingfisher Mechanical Engineering Limited | Professional & scientific | 2017 |
| Kirby Building & Refurbishment Ltd | Construction | 2012 |
| Kirsty Hoskins Limited | Administrative & support | 2019 |
| Kitchen Team 462 | | 2003 |
| Kitchen Team 707 | | 2003 |
| KK & Sons Group Ltd | Financial services | 2020 |
| Klevar Ltd | Manufacturing | 2018 |
| Klim Associates Ltd | Professional & scientific | 2006 |
| Kljw Services Limited | Administrative & support | 2009 |
| KML Digswell Limited | Arts & recreation | 2018 |
| KMP Importers & Exporters Ltd | Wholesale & retail | 2025 |
| Kmprint Finishing Ltd | Information & communication | 2007 |
| KMQ Consulting Limited | Information & communication | 2019 |
| Knight Stanley Ltd | Real estate | 2021 |
| Knightsfield Nursery & Pre-School C.I.C. | Health & social care | 2022 |
| Knightsfield Pre-School | Education | 2010 |
| Knightsfield School | Education | 2012 |
| Knockmore Electrical Ltd | Construction | 2026 |
| Kolamala Ltd | Real estate | 2022 |
| Kollabr Ltd | Information & communication | 2026 |
| Koroglu Ltd | Real estate | 2019 |
| Krapow Franchise Ltd | Hospitality | 2026 |
| Kretserco Holdings Limited | Financial services | 2025 |
| Kretserco Management Consulting Ltd. | Professional & scientific | 2024 |
| Kronan Security Systems Ltd | Administrative & support | 2016 |
| KS Travel Ltd | Transport & logistics | 2020 |
| KTS Accountancy Limited | Professional & scientific | 2006 |
| Kudos Internet Limited | Information & communication | 2022 |
| Kunex Holdings Limited | Wholesale & retail | 2020 |
| Kuraudo Ltd | Professional & scientific | 2018 |
| Kutchenhaus Welwyn Garden City Limited | Professional & scientific | 2024 |
| KX Services Limited | Professional & scientific | 2023 |
| Kymo Care Ltd | Public administration | 2026 |
| L & D Window Restoration Limited | Construction | 2019 |
| L a Carpentry Maintenance & Renovations Ltd | Construction | 2015 |
| L Bennett & SON Holdings Limited | Wholesale & retail | 2003 |
| L E H Properties Ltd | Real estate | 2022 |
| L S Autos Service Diagnostic and Repairs Limited | Wholesale & retail | 2022 |
| L V L Property Limited | Real estate | 2021 |
| L. Bennett & SON Limited | Wholesale & retail | 1971 |
| L2 Digital Ltd | Professional & scientific | 2018 |
| LA Themba Kensington Ltd | Construction | 2010 |
| Labtronics Design Ltd | Professional & scientific | 2022 |
| Ladywealth’S Kitchen Ltd | Hospitality | 2025 |
| Ladywell Dvlps Limited | Other services | 2021 |
| Ladywell Homes Limited | Construction | 2016 |
| Lakehouse Nurseries Ltd | Health & social care | 2009 |
| Lambano Ltd | Health & social care | 2021 |
| Lamberts Florists Ltd. | Wholesale & retail | 1997 |
| Lambodara Enterprise Limited | Hospitality | 2013 |
| Lana Investments Limited | Financial services | 2019 |
| Lance and Shield Limited | Hospitality | 2023 |
| Landmark FS Solutions Ltd | Extraterritorial | 2015 |
| Langdon Property Group Ltd | Real estate | 2022 |
| Laszlo Kertai Transport Limited | Transport & logistics | 2011 |
| Launchgrain Limited | Administrative & support | 2004 |
| Lavendon Aggregates Limited | Mining & quarrying | 2024 |
| Layton Street Freehold Company Ltd | Households | 2017 |
| Lazurite Dermaceuticals Ltd | Manufacturing | 2021 |