| Long Acres Residents Management Company Limited | Households | 2015 |
| Longevity Strategy Ltd | Professional & scientific | 2020 |
| Longforte Trading Limited | Wholesale & retail | 2015 |
| Longview Stud & Bloodstock Ltd | Agriculture & fishing | 1981 |
| Lookcustom GB Limited | Manufacturing | 2001 |
| Lookcustom U.K. Limited | Wholesale & retail | 1993 |
| Looks Good Graphics Ltd | Professional & scientific | 2020 |
| Loom & Light Ltd | Wholesale & retail | 2024 |
| Loonsal Ltd | Construction | 2019 |
| Loop Contracts Limited | Real estate | 2012 |
| Loop Investments Limited | Administrative & support | 2012 |
| Loop Lettings Ltd | Real estate | 2015 |
| Loop Redbrick Ltd | Real estate | 2022 |
| Lord Percival Limited | Real estate | 2024 |
| Lorden Homes Limited | Construction | 2024 |
| Lords SFX Ltd | Information & communication | 2019 |
| Lorenc Lift Installation Limited | Construction | 2025 |
| Lorien Investments Ltd | Financial services | 2019 |
| Loritaur Limited | Professional & scientific | 2016 |
| Lorna K Ltd | Health & social care | 2019 |
| Lorriman Marketing and Communications Limited | Professional & scientific | 2024 |
| Loss Prevention Certification Board Limited(The) | Professional & scientific | 1985 |
| Lothardan Limited | Administrative & support | 2016 |
| Lotstar Limited | Health & social care | 2012 |
| Lotto Limited | Extraterritorial | 2009 |
| Lottus Group Ltd | Real estate | 2015 |
| Lottus Property Group Ltd | Real estate | 2021 |
| Lotus Eyes Ltd | Administrative & support | 2013 |
| Lotus Foods Trading Company UK Limited | Wholesale & retail | 2018 |
| Lotus ZRG Limited | Water & waste | 2019 |
| Lotuscourt Residents Company Limited | Real estate | 1987 |
| Loughran Consulting Ltd | Information & communication | 2012 |
| Loughran Idse Limited | Professional & scientific | 2023 |
| Louie H Barbers Ltd | Other services | 2024 |
| Louis Campbell Ltd | Wholesale & retail | 2025 |
| Louise Cherry Limited | Professional & scientific | 2024 |
| Louise Emily Fitness Ltd | Arts & recreation | 2024 |
| Lovage Limited | Households | 1987 |
| Love for Web Limited | Information & communication | 2016 |
| Love Hemp Investments Ltd | Financial services | 2023 |
| Love Loops Studio Limited | Wholesale & retail | 2025 |
| Love Revolution Limited | Information & communication | 2009 |
| Love, Jakey Ltd | Professional & scientific | 2022 |
| Lovescleaningcompany.Com Ltd | Administrative & support | 2025 |
| Lower Paddock Freehold Limited | Households | 2011 |
| Lowstream Property Management Limited | Households | 1982 |
| Loxton Publishers Limited | Real estate | 1961 |
| Loxwood House Ltd | Health & social care | 2004 |
| LP & IA Associates Limited | Wholesale & retail | 2023 |
| LPC Construction Limited | Construction | 1997 |
| LPC Developments Limited | Real estate | 2014 |
| LPG Group Ltd | Construction | 2018 |
| LPJ Property Limited | Real estate | 2023 |
| Lprg (Listen, Participate, Reflect & Grow) Ltd | Other services | 2024 |
| LPS Accountants Limited | Administrative & support | 2018 |
| LPS Livingstone Audit Limited | Professional & scientific | 2020 |
| LPS Livingstone Limited | Professional & scientific | 2011 |
| LR Sky Limited | Administrative & support | 2024 |
| LRB Property Management Ltd | Real estate | 2021 |
| LRC (Watford) Limited | Water & waste | 2011 |
| Lrhorne Investments Limited | Wholesale & retail | 2020 |
| Lris Limited | Real estate | 2017 |
| Lrps Properties Ltd | Real estate | 2024 |
| Lrrzm Property Limited | Real estate | 2018 |
| LRS Independent Educational Psychology Services Ltd | Health & social care | 2016 |
| LS Electrix Ltd | Construction | 2020 |
| LS Steak House Ltd | Hospitality | 2025 |
| LSA Bistro Ltd | Hospitality | 2020 |
| Lsaw Ltd | Administrative & support | 2026 |
| LSD Carpentry Ltd | Construction | 2018 |
| Lssk Services Ltd | Health & social care | 2022 |
| LT Jewellery Ltd | Manufacturing | 2021 |
| LTF Consultants Ltd | Administrative & support | 2018 |
| LTF Creative Ltd | Professional & scientific | 2019 |
| LTJ Consulting Limited | Professional & scientific | 2020 |
| LTK Digital Ltd | Information & communication | 2023 |
| LTL (London) Limited | Administrative & support | 2002 |
| LTL Commercial Services Ltd | Manufacturing | 2026 |
| LU & Tori Property Ltd | Real estate | 2021 |
| Lucas Barbosa Ltd | Administrative & support | 2025 |
| Lucas Electrical Contractors (Watford) Limited | Construction | 2017 |
| Lucian & Lucia Limited | Administrative & support | 2024 |
| Lucian Lupu Ltd | Construction | 2020 |
| Lucianleny Ltd | Construction | 2019 |
| Lucid Horizons Ltd | Professional & scientific | 2020 |
| Lucilda Bailey Ltd | Professional & scientific | 2026 |
| Lucketts Air Travel Limited | Administrative & support | 2009 |
| Lucketts Asset Management Limited | Wholesale & retail | 2024 |
| Lucketts Coaches Limited | Transport & logistics | 2023 |
| Lucketts Estates Limited | Real estate | 2021 |
| Lucketts Group Limited | Financial services | 2016 |
| Lucketts Management Services Limited | Professional & scientific | 2024 |
| Lucketts Midlands Limited | Transport & logistics | 2022 |
| Lucketts of Watford Limited | Transport & logistics | 1996 |
| Lucky AM to PM Ltd | Wholesale & retail | 2025 |
| Lucky Innotech Solutions Limited | Information & communication | 2012 |
| Lucky Lesson Ltd | Health & social care | 2022 |
| Lucky Property Investment Ltd | Real estate | 2022 |
| Luckyhealth Limited | Health & social care | 2019 |
| Lucy Joseph Ltd | Professional & scientific | 2018 |