| LIM ERP Ltd | Administrative & support | 2013 |
| Lime Tree Acupuncture Limited | Health & social care | 2024 |
| Lime Tree Community Acupuncture CIC | Health & social care | 2025 |
| Limestoneuk Limited | Other services | 2015 |
| Lisa’S Lily Whites Limited | Administrative & support | 2024 |
| Lister Interiors Limited | Wholesale & retail | 2011 |
| Listplace Limited | Real estate | 1981 |
| Little Blue Box Limited | Professional & scientific | 2013 |
| Little Saddles Ltd | Real estate | 2021 |
| Lloyds of Watford LLP | | 2005 |
| Lomas & Garner Limited | Wholesale & retail | 2005 |
| London Chauffeurs Network Ltd | Transport & logistics | 2024 |
| London City Builder 1 Ltd | Construction | 2023 |
| London Heritage Stone Limited | Construction | 2015 |
| London Specialist Services Limited | Real estate | 2002 |
| London Surface Design Limited | Professional & scientific | 2019 |
| Lone Star Facilities Limited | Households | 2021 |
| Lopatin Consulting Limited | Administrative & support | 2014 |
| Lotus Shelter LLP | | 2022 |
| Lotus Shelter MK Ltd | Real estate | 2024 |
| Louella Property Limited | Construction | 2004 |
| Love Car Deals Ltd | Wholesale & retail | 2024 |
| Love Peachy Ltd | Wholesale & retail | 2020 |
| LS Collective Movement Limited | Arts & recreation | 2026 |
| Luemi Limited | Construction | 2024 |
| Lujay Ltd | Financial services | 2024 |
| Lumley Estates Limited | Real estate | 2003 |
| Luna Medical Service Limited | Health & social care | 2024 |
| Lutodata Consultancy Ltd | Information & communication | 2017 |
| LUV IT (2010) Limited | Wholesale & retail | 2010 |
| Luxoro Ltd | Transport & logistics | 2025 |
| Luxury Sassy Escapes Ltd | Administrative & support | 2025 |
| Lynda Dullop Consulting Services Ltd | Professional & scientific | 2022 |
| Lyne Still Limited | Health & social care | 2024 |
| Lystems Ltd | Wholesale & retail | 2026 |
| M Sims Properties Ltd | Real estate | 2024 |
| Made Motorsport Group Limited | Professional & scientific | 2018 |
| Made Worldwide Ltd | Professional & scientific | 2013 |
| Made WW Limited | Professional & scientific | 2024 |
| Maggie Grace Limited | Real estate | 2014 |
| Majestic Apartments (NO. 125) RTM Company Limited | Households | 2020 |
| Majestic Apartments (NO. 127) RTM Company Limited | Households | 2020 |
| Malicorp Limited | Construction | 1997 |
| Malthouse Place Residents' Association (Radlett) Limited | Other services | 1992 |
| Mambo Wallet Limited | Information & communication | 2025 |
| MANISH.CO-1 Ltd | Information & communication | 2022 |
| Manor Lodge School | Education | 1993 |
| Mantori Developments Limited | Construction | 2022 |
| Mantori Homes Ltd | Construction | 2023 |
| MAP (Cambridge) Limited | Professional & scientific | 2018 |
| Maple Health UK Limited | Health & social care | 2007 |
| Mapp Estates Limited | Real estate | 2002 |
| Maptarn Limited | Real estate | 1998 |
| Markfield Properties Ltd | Real estate | 2019 |
| Maronbridge Limited | Real estate | 1998 |
| Marsden Court (Radlett) Management Co. Limited | Households | 1993 |
| Masai 5 Limited | Hospitality | 2017 |
| Mason Capital International Limited | Professional & scientific | 2023 |
| Mason Chauffeurs Ltd | Transport & logistics | 2022 |
| Masonic Hall (Radlett) Limited | Other services | 1958 |
| Master Chauffeurs Ltd | Transport & logistics | 2025 |
| Master Works Limited | Administrative & support | 2008 |
| Mastery AI Ltd | Information & communication | 2024 |
| Mathewson's General Practice Group Ltd | Health & social care | 2025 |
| Maurice Charge Limited | Arts & recreation | 2006 |
| Mayclo Property Ltd | Administrative & support | 2022 |
| Maytrees Residents Association Limited | Households | 1985 |
| Mazal Plumbing and Electrical Limited | Construction | 2026 |
| MB LUX Limited | Transport & logistics | 2023 |
| Mc&A Consulting Ltd | Professional & scientific | 2013 |
| Mccabe Accounting Services Ltd | Professional & scientific | 2020 |
| Mcgowan Property Investments LLP | | 2009 |
| Mcgregor Upstream Consultants Limited | Professional & scientific | 2017 |
| MD Project Design Limited | Professional & scientific | 2018 |
| MED Info 20.20 Limited | Professional & scientific | 2008 |
| Medes Ltd. | Administrative & support | 1995 |
| Medical Logistics Limited | Health & social care | 2014 |
| Medridge Limited | Administrative & support | 2021 |
| MEE My Eco Energy Ltd | Information & communication | 2023 |
| Meermal Limited | Real estate | 2022 |
| Meetwagons Limited | Transport & logistics | 2003 |
| Mega BID Ltd | Information & communication | 2026 |
| MEI Quan Academy of TAI CHI Limited | Arts & recreation | 2013 |
| Meliora Innovation Ltd | Manufacturing | 2021 |
| Memz Travel Ltd | Transport & logistics | 2024 |
| Mentpoint Limited | Administrative & support | 1978 |
| Menzies Media Limited | Professional & scientific | 2018 |
| Merenge Foods Ltd | Manufacturing | 2012 |
| Mereoak Trading Limited | Real estate | 2016 |
| Meritdream Limited | Real estate | 1999 |
| Merson Construction Ltd | Construction | 2025 |
| Merston Investments Limited | Administrative & support | 1982 |
| Mesmer Wellbeing Ltd | Health & social care | 2026 |
| Metal & Waste Recycling Limited | Water & waste | 2021 |
| Metal Doors and More Limited | Construction | 2025 |
| Metisacre Limited | Administrative & support | 1996 |
| MG Marketing Ltd. | Administrative & support | 2020 |
| MG Wellness Ltd | Public administration | 2025 |
| MGG Brickwork Ltd | Construction | 2025 |
| Mgwl Limited | Wholesale & retail | 2011 |