| Lots of Rice Ltd | Hospitality | 2019 |
| Loudoun Coachworks (London) Limited | Extraterritorial | 1963 |
| Love Vintage Ltd | Wholesale & retail | 2021 |
| Ltgds Realisations Limited | Professional & scientific | 1965 |
| Lush (Heat Treatment) Limited | Manufacturing | 1987 |
| Luton Professional Cleaning Co Ltd | Administrative & support | 2024 |
| Luxury Computer Services Limited | Professional & scientific | 1991 |
| M D H Derivatives Limited | Financial services | 2006 |
| M. & J. Building Company Limited | Wholesale & retail | 1984 |
| M.A. Ashley & Sons Limited | Wholesale & retail | 1958 |
| M.S.G.S. Healthcare Limited | Health & social care | 2017 |
| M.V.B. Components Limited | | 1981 |
| M8 GP Engineering Ltd | Professional & scientific | 2025 |
| Macs Neighbourhood Centres Limited | Construction | 1961 |
| Maftec Limited | Professional & scientific | 2004 |
| Magic Systems Limited | Information & communication | 1985 |
| Magpie Catering Limited | Hospitality | 2007 |
| Magtron Limited | Transport & logistics | 1992 |
| MAJ X Ltd | Information & communication | 2015 |
| Malik & Sons Investments Limited | Real estate | 2009 |
| Malikshaw Limited | Information & communication | 2006 |
| Maltings Locksmiths Ltd | Other services | 2022 |
| Manasvi Limited | Real estate | 2022 |
| Manor Consulting Services Limited | Information & communication | 2004 |
| Manor Fish Bar (Wallington) Limited | Hospitality | 2005 |
| Manor of Groves Limited | Hospitality | 1996 |
| Mansard Close Residents Association Limited | Real estate | 1977 |
| Marden Hill Residents Association Limited | Households | 1979 |
| Margrave Communications Limited | Professional & scientific | 2006 |
| Mark Winter Homes Limited | Construction | 2006 |
| Marman Ltd | Professional & scientific | 2019 |
| Marques 100 Limited | Real estate | 2007 |
| Mary's of Enfield Limited | Wholesale & retail | 2001 |
| MAS Intimates UK Limited | Manufacturing | 2006 |
| Mastercraft Carpentry Limited | Construction | 2005 |
| Masterlay Products Limited | Manufacturing | 1988 |
| Matevol Automation Company Limited | | 1967 |
| Matt Hackett Design Ltd | Administrative & support | 2006 |
| Maverstone Properties Limited | Real estate | 2002 |
| Maydart Limited | | 1977 |
| Mcaleer and French Construction Limited | | 1983 |
| Mccourt Sales & Lettings LLP | | 2018 |
| Mclaughlin Management Limited | Professional & scientific | 2017 |
| Mcmullen & Sons, Limited | Manufacturing | 1897 |
| Mcmullen's of Hertford Limited | Hospitality | 1956 |
| Mcnulty Landscape Construction Ltd | Other services | 2017 |
| Mead Investments (Hinxworth) Ltd | Real estate | 2007 |
| Medic Galleria International Ltd | Real estate | 2022 |
| Meridian Building Plastics Limited | Wholesale & retail | 2005 |
| Meridian Inns (Northern) Limited | | 1981 |
| Merriman Holdings Limited | | 1989 |
| Met-Seam Limited | Administrative & support | 2005 |
| MGG (Investments) Limited | Real estate | 2004 |
| MHP Claims Solutions Limited | Financial services | 2009 |
| Michelle Coles Limited | Health & social care | 2006 |
| Micklethwaite Properties Limited | Professional & scientific | 2004 |
| Mid-Herts Golf Club (Land) Limited | Arts & recreation | 1936 |
| Midator Limited | Professional & scientific | 1976 |
| Mill END Service Centre Ltd | Wholesale & retail | 2013 |
| Mill Soft Toys Limited | | 1987 |
| Millennia Network Consultancy Limited | Information & communication | 1996 |
| Millers Salons Limited | Other services | 2006 |
| Minsden Limited | Extraterritorial | 2005 |
| Mirach Ltd | Hospitality | 2022 |
| Mirelis Limited | Wholesale & retail | 2003 |
| Missedabit.Com Ltd | Information & communication | 2005 |
| MMD Financial Services Ltd | Financial services | 2018 |
| MNK Co Solutions Ltd | Health & social care | 2025 |
| Modern Air (U.K.) Limited | Other services | 1988 |
| Moledina Bros Limited | Professional & scientific | 1994 |
| Monument Real Estate Limited | Real estate | 2022 |
| Mookie Pet Limited | Administrative & support | 2011 |
| Moonraker Group Limited | Other services | 1990 |
| Morgan Rose Limited | Professional & scientific | 1997 |
| Morse Flexon Limited | | 1982 |
| Mountford Chemists Limited | Wholesale & retail | 1988 |
| MRC Products Limited | | 1981 |
| MSH Properties (Investment) Limited | Other services | 2007 |
| MSL Estates Limited | Professional & scientific | 2010 |
| Mtek Systems Limited | Information & communication | 2007 |
| Multi-User Group Limited | Financial services | 2002 |
| Multi-User Systems Limited | Information & communication | 1988 |
| Multiple Sclerosis Trust (Education) Limited | Education | 2004 |
| Multitrade Building Limited | Construction | 2006 |
| Muon Code Limited | Information & communication | 2025 |
| Murray Memorial Service Limited | Other services | 1988 |
| Music Bloc Limited | Information & communication | 2022 |
| Mustang Ventures Ltd | Wholesale & retail | 2026 |
| MVI Van Installations Ltd | Manufacturing | 2025 |
| N.T.M. Garages Limited | Wholesale & retail | 1979 |
| Nairobi Coffee and Tea Company (Overseas) Limited(The) | Extraterritorial | 1986 |
| Nairobi Coffee and Tea Company Limited(The) | Manufacturing | 1945 |
| Napchester UK Ltd | Agriculture & fishing | 2023 |
| Nazco Limited | Real estate | 1997 |
| NBM Publishing Ltd | Manufacturing | 2006 |
| NCM Flooring Services Limited | Construction | 2008 |
| Nelson Browne Management Limited | Administrative & support | 2007 |
| New AGE Motor Sales Limited | Wholesale & retail | 2004 |
| New Hermitate Halls and Ballroom Limited(The) | | 1961 |
| New Seasons Installations (Colindale) Limited | | 1982 |