| KW RTM Company Ltd | Households | 2006 |
| Kynance Business Consulting Limited | Administrative & support | 2019 |
| L & B Flooring Limited | Construction | 2025 |
| L & C York Holdings Limited | Financial services | 2019 |
| L & D Plumbing & Heating Ltd | Construction | 2015 |
| L B Venue Trading Ltd | Administrative & support | 2024 |
| L E D Builders Limited | Construction | 2003 |
| L Oliver and SON Roofing Contractors Ltd | Construction | 2021 |
| L P Pallett Quarry (Feltwell) Ltd | Mining & quarrying | 2016 |
| L P Pallett Quarry (Henham) Limited | Mining & quarrying | 2014 |
| L S F Horticultural Advisory Services Ltd | Administrative & support | 2025 |
| L T Pallet & SON Limited | Manufacturing | 2015 |
| L Welsh Consultancy Ltd | Information & communication | 2023 |
| L&C Building Contractors Ltd | Construction | 2025 |
| L&Q Logistics Ltd | Transport & logistics | 2025 |
| L. Chernin Plumbing & Heating Limited | Construction | 2016 |
| L. P. Pallett Quarry Limited | Mining & quarrying | 2011 |
| L.E.W Consultancy Ltd | Professional & scientific | 2021 |
| L.N.D. Trading Ltd | Wholesale & retail | 2025 |
| L.P.S Resource GB Limited | Transport & logistics | 2024 |
| LA FEE LLP | | 2008 |
| LA Yeoman Foods Limited | Manufacturing | 2004 |
| Laar Building Limited | Construction | 2025 |
| Lacey Construction Ltd | Construction | 2022 |
| Lacey Heating Homecare Ltd | Construction | 2024 |
| Lacey Heating Ltd | Construction | 2021 |
| Ladkarn Construction Limited | Construction | 1983 |
| Lady Jane Limited | Wholesale & retail | 2018 |
| Ladygrove Investments Limited | Professional & scientific | 2021 |
| Lakehouse Properties Limited | Real estate | 2025 |
| Lancaster Gate East (Hendon) Management Company Limited | Households | 1989 |
| Landrise Holdings Limited | Construction | 2020 |
| Lanes Recruitment Ltd | Administrative & support | 2018 |
| Lanesra FC Ltd | Construction | 2025 |
| Langley Road (Watford) Management Company Limited | Households | 2005 |
| Langley's Property Development Ltd | Construction | 2020 |
| Langtry Leisure Ltd | Hospitality | 2018 |
| Lansdown Strategic Capital Ltd | Professional & scientific | 2019 |
| Lapada Events Ltd | Administrative & support | 2022 |
| Lapb Promotions Ltd | Administrative & support | 2024 |
| Lapinou Chouchou Ltd | Wholesale & retail | 2025 |
| Larbey Evans Ltd | Administrative & support | 2009 |
| Lares Relocation Services Ltd | Transport & logistics | 2018 |
| Larkbarrow Limited | Professional & scientific | 2018 |
| Laser on Tour Ltd | Other services | 2021 |
| Last Minute BUS Ltd | Transport & logistics | 2023 |
| Latch Events Limited | Administrative & support | 2021 |
| Latchglen Limited | Financial services | 1978 |
| Laud Limited | Wholesale & retail | 2024 |
| Launching PAD Ltd | Administrative & support | 2025 |
| Laurel Court Residents Company Limited | Households | 2010 |
| Lauren Sydney Ltd | Other services | 2026 |
| Lautus Limited | Real estate | 2006 |
| Lavant House Ltd | Information & communication | 2008 |
| Lawes Recruitment (UK) Limited | Administrative & support | 2005 |
| Lawson Cook Limited | Professional & scientific | 2019 |
| LAYER1 Properties Limited | Administrative & support | 2024 |
| Lbrowne Property Limited | Real estate | 2015 |
| LCM Herts Ltd | Wholesale & retail | 2026 |
| LEA Motors Limited | Wholesale & retail | 1993 |
| Leaf Consultants Limited | Professional & scientific | 2020 |
| Leal Accountants Limited | Professional & scientific | 2012 |
| Leap Recruitment Partners Limited | Administrative & support | 2017 |
| Learn Away Limited | Administrative & support | 2018 |
| Learn to Dream Limited | Manufacturing | 2002 |
| Learn With JEN Limited | Education | 2023 |
| LEARN2SWIM (Herts) Ltd | Health & social care | 2016 |
| Learning Without Limits Limited | Administrative & support | 2015 |
| LEE & Co London Limited | Other services | 2017 |
| Legal & Commercial Services (1996) Limited | Professional & scientific | 1995 |
| Legra 2020 Limited | Construction | 2017 |
| LEN Creative Limited | Administrative & support | 2014 |
| LEN Spooner Consulting Limited | Professional & scientific | 2011 |
| Leo's Gym Amateur Boxing Club CIC | Arts & recreation | 2025 |
| Leo's House DOT COM Ltd | Real estate | 2025 |
| Leocam Ltd | Professional & scientific | 2021 |
| Leopardon Care Limited | Administrative & support | 2021 |
| Let's Talk Animals C.I.C. | Arts & recreation | 2021 |
| Letcetra Limited | Real estate | 2012 |
| Letsbsmart Limited | Real estate | 2022 |
| Level UP Logistics Ltd | Transport & logistics | 2023 |
| Levin Trading Limited | Wholesale & retail | 2019 |
| Lexden Properties Limited | Real estate | 2017 |
| LG Garage Ltd | Wholesale & retail | 2014 |
| LGR Global Limited | Administrative & support | 2025 |
| Liberty Building Company Ltd | Construction | 2014 |
| Lifelink Services Limited | Financial services | 2000 |
| Lifetime Mortgages & Finance Limited | Financial services | 2003 |
| Light & Bough Limited | Manufacturing | 2022 |
| Lighting Design Solutions Limited | Administrative & support | 2008 |
| Lime Kiln Creative Ltd | Professional & scientific | 2017 |
| Limitless Community Boxing Project CIC | Arts & recreation | 2022 |
| Limitless Films Limited | Information & communication | 2025 |
| Lincoln's Farm & Investments Limited | Real estate | 2009 |
| Lincoln’S Tyre Service (AJS) Limited | Wholesale & retail | 2018 |
| Linden Court Garages Limited | Households | 1983 |
| Linden Court Maintenance Limited | Households | 1959 |
| Linden Lodge Winchmore Hill Management Limited | Households | 1994 |
| Linds Properties Ltd | Real estate | 2022 |
| Linfeng Limited | Hospitality | 2023 |