| Jmak Solutions Limited | Professional & scientific | 2006 |
| JMP Business Associates Ltd | Professional & scientific | 1999 |
| JN Tyres Autocare Ltd | Wholesale & retail | 1964 |
| Jodonkim Limited | Information & communication | 1989 |
| John O'Conner (Grounds Maintenance) Limited | Professional & scientific | 1991 |
| John Worley (Memorials) Limited | Other services | 1991 |
| JR Systems Installations Ltd | Information & communication | 2014 |
| K.Brind Physiotherapy Limited | Other services | 2007 |
| K.H.C. Management Company Limited | Households | 1975 |
| KAD Environmental Consultancy Limited | Professional & scientific | 2005 |
| Kalm Accounting Ltd | Professional & scientific | 2023 |
| Kamelee Ltd | Wholesale & retail | 2015 |
| Katsu Charlie Ltd | Other services | 2017 |
| Kaybec Ltd | Construction | 2021 |
| Kayleigh Development Limited | Professional & scientific | 1989 |
| KD Automotive Solutions Limited | Other services | 2022 |
| Kedia Nivas Ltd | Real estate | 2024 |
| Keirstan Carpentry Limited | Construction | 2006 |
| Kingfisher Damp Seal Limited | | 1983 |
| Kingfisher Nurseries Limited | Other services | 1989 |
| Kings Ride Limited | Arts & recreation | 2003 |
| Kingsboro Contractors Limited | Construction | 2001 |
| Kingsbury Watermill Limited | Hospitality | 1964 |
| Kinreask Construction Limited | Construction | 2012 |
| Kinsman Red Limited | Professional & scientific | 1991 |
| Kirby Colletti Lettings Limited | Real estate | 2005 |
| KJJ Investments Limited | Real estate | 2015 |
| Klmt Consulting Ltd | Other services | 2022 |
| KMR Investments Ltd | Real estate | 2020 |
| Knight Haulage Limited | Transport & logistics | 2011 |
| Krish EST Ltd | Professional & scientific | 2015 |
| Kryonet Limited | Wholesale & retail | 2000 |
| Kyle Stewart Executive Pension Trustee Limited | Financial services | 1984 |
| L . a . Woolner Ltd. | Construction | 2002 |
| L.M.H. (Management Services) Limited | Professional & scientific | 1976 |
| LA Boucherie (Holdings) Limited | Administrative & support | 2004 |
| LA Boucherie (Kosher) Limited | Hospitality | 1985 |
| LA Boucherie Express Limited | Wholesale & retail | 2005 |
| LA MER Solutions Limited | Administrative & support | 2012 |
| Labrose Properties Limited | Wholesale & retail | 1984 |
| Ladoucette Consulting Limited | Administrative & support | 2010 |
| Ladyheath Limited | Real estate | 2006 |
| Lakeland Holiday Park Limited | Hospitality | 1973 |
| Lakepoint Estates Limited | Real estate | 2001 |
| Lamek Limited | Extraterritorial | 2001 |
| Land Searches Bureau Limited | Real estate | 2006 |
| Landlord Repairs & Maintenance Services Limited | Other services | 2019 |
| Landranks Property Co. Limited | Professional & scientific | 1974 |
| Lane & Skillen Limited | Construction | 2008 |
| Langford and Langford Co Ltd | Real estate | 2014 |
| Langley Electrical Contractors Limited | Construction | 2018 |
| Langley Transport Limited | Wholesale & retail | 1959 |
| Langmoor Orchard (H K L M) Management Company Limited | Households | 1995 |
| Lankesters Limited | Professional & scientific | 2007 |
| Laurel Lodge Limited | Health & social care | 2003 |
| Lava Cookware UK Ltd | Wholesale & retail | 2018 |
| Lawson Bueno & Co Limited | Administrative & support | 2013 |
| Lawton Prior & Mecklenburgh Limited | Professional & scientific | 1988 |
| Lazarus Design and Construction Ltd | Real estate | 2018 |
| LB Design Projects Ltd | Professional & scientific | 2026 |
| LBM UK Limited | Wholesale & retail | 1972 |
| Lcat Ltd | Professional & scientific | 2013 |
| LDY Technical Services Limited | | 1976 |
| Leading Bricks Ltd | Professional & scientific | 2020 |
| Leading Note Limited | Arts & recreation | 2011 |
| Lear Travel Limited | Administrative & support | 2011 |
| Leaside Turned Parts Limited | Manufacturing | 1987 |
| Leaver and Hildrick Limited | | 1963 |
| Lebbi UK Ltd | Wholesale & retail | 2007 |
| Leden Properties Limited | Real estate | 2003 |
| LEE Koffman Ltd | Other services | 2026 |
| Legal & Property Limited | Professional & scientific | 2007 |
| Leisurewheels Limited | Wholesale & retail | 2012 |
| Letchworth Car Care Limited | Wholesale & retail | 2003 |
| Letchworth Catering Ltd | Hospitality | 2023 |
| Letcombe Limited | Professional & scientific | 1989 |
| Lettings Domain Ltd | Real estate | 2009 |
| Levelcomp Limited | Construction | 1993 |
| Lewis Bathrooms Limited | Construction | 2024 |
| Lewis Partners Limited | Professional & scientific | 2004 |
| Lewis Sidhu Legal Limited | Professional & scientific | 2013 |
| Libra Computers Limited | Information & communication | 1996 |
| Libra Developments Limited | Real estate | 1990 |
| Lifeline Management | | 2003 |
| Light Tribe Ltd | Manufacturing | 2025 |
| Lily and Bear Productions Limited | Arts & recreation | 2007 |
| Lindens Freehold Limited | Professional & scientific | 2002 |
| Linecall Limited | Information & communication | 1993 |
| Liscomb Limited | Financial services | 2007 |
| Litrbull Ltd | Information & communication | 2025 |
| Livinglife Publications Ltd | Information & communication | 2023 |
| LJP Electrical Limited | Construction | 2006 |
| Lloyds & Company Letchworth Limited | Manufacturing | 1920 |
| LMR Building Contractors Limited | Construction | 2004 |
| Lodge Dental Suite Ltd | Health & social care | 2024 |
| London Nordic Ltd | Financial services | 1967 |
| London Town Bakeries Limited | Transport & logistics | 1989 |
| Loony Records Limited | Information & communication | 2006 |
| Lordvale Limited | Real estate | 2005 |
| Lotfolds Ltd | Wholesale & retail | 2022 |