| Lucy Pittaway Fine Art Limited | Manufacturing | 2017 |
| Lucy Pittaway Ltd | Manufacturing | 2015 |
| Lumberton Finance Limited | | 2024 |
| Luminel Limited | Information & communication | 2016 |
| Luna Access Ltd | Manufacturing | 2023 |
| Lunelle Nails & Beauty Ltd | Other services | 2025 |
| Lunzer Wine Group Limited | Wholesale & retail | 2015 |
| Lupine Investments Ltd | Real estate | 2022 |
| LUV Financial Ltd | Financial services | 2018 |
| Luxe Tanning Salon Ltd | Other services | 2025 |
| LVC Consulting Limited | Information & communication | 2023 |
| LWA Ltd | Professional & scientific | 2025 |
| LWG Group Limited | Financial services | 2012 |
| Lwsg Ltd | Wholesale & retail | 2025 |
| Lxen Electrical & Security Ltd | Construction | 2023 |
| LY Sparkle Limited | Hospitality | 2020 |
| Lydia Kimmerling Ltd | Education | 2023 |
| Lyndhurst & Partners Ltd | Wholesale & retail | 2025 |
| Lyvlee Limited | Wholesale & retail | 2010 |
| M & a Bainbridge Ltd | Agriculture & fishing | 2022 |
| M & J Auto Mechanics LLP | | 2010 |
| M and H Project Services Limited | Professional & scientific | 2022 |
| M Costa Consulting Ltd | Professional & scientific | 2019 |
| M H Thwaites Building & Restoration Limited | Construction | 2012 |
| M Metcalfe Contracting Limited | Agriculture & fishing | 2015 |
| M Nadal and Co Limited | Financial services | 2009 |
| M T T Executive Limited | Administrative & support | 2009 |
| M W Pigs Limited | Agriculture & fishing | 2018 |
| M&J Holdings Ltd | Administrative & support | 2018 |
| M&L Inns Ltd | Hospitality | 2019 |
| M&T Advisory Ltd | Professional & scientific | 2025 |
| M. Arrowsmith Limited | Wholesale & retail | 2003 |
| M. Z. O. U. K. Holdings (O.S.B.) Limited | Wholesale & retail | 2022 |
| M.A. Hunt Limited | Wholesale & retail | 2005 |
| M.A.G. Building Services Limited | Construction | 2002 |
| M.E. Nicholls Conversions Limited | Real estate | 1960 |
| M.H.T. Technology Limited | Other services | 1994 |
| M.I. Haul Limited | Wholesale & retail | 2010 |
| M.Putkisto Limited | Other services | 2012 |
| M.S. Macbeth Limited | Financial services | 1997 |
| M.W. Waste Drainage Support Services Limited | Water & waste | 2011 |
| M.Z.Oweiss & Sons (U.K) Limited | Other services | 1972 |
| MAA Property Limited | Real estate | 2021 |
| MAA Medic Ltd | Health & social care | 2015 |
| Mabco Limited | Professional & scientific | 2002 |
| Mabd Services Ltd | Administrative & support | 2016 |
| MAC Plant Hire Limited | Administrative & support | 2003 |
| Macarong KEW Limited | Hospitality | 2023 |
| Macbeth Group Holdings Ltd | Financial services | 2022 |
| Macbeth Group Ltd | Extraterritorial | 2022 |
| Macbeth Premium Finance Limited | Financial services | 2003 |
| Mack-Brooks Exhibitions Limited | Administrative & support | 1969 |
| Macro Trading Edge Ltd | Information & communication | 2010 |
| Macrofa Ltd | Agriculture & fishing | 2026 |
| Madam Jacks Ltd | Extraterritorial | 2015 |
| Madsen Reid Engineering Consultants Limited | Professional & scientific | 2014 |
| Magartus Limited | Extraterritorial | 2011 |
| Magenta & Key Ltd | Information & communication | 2025 |
| Magenta Digital Limited | Information & communication | 2011 |
| Magenta Direct Investments Limited | Financial services | 2021 |
| Magenta Public Relations Limited | Professional & scientific | 2012 |
| Magic Breaks Limited | Administrative & support | 2018 |
| Magic Medicine Studios Ltd | Information & communication | 2013 |
| Magma Safety Products Limited | Manufacturing | 1992 |
| Magnet Grooming Limited | Other services | 2022 |
| Maham Limited | Other services | 2012 |
| Mahee-Mountain Ltd | Other services | 2012 |
| MAI VU Limited | Administrative & support | 2007 |
| Maida Vale Maintenance Limited | Administrative & support | 2003 |
| Maidenscott Properties Ltd | Real estate | 2020 |
| Maidstone Library Limited | Real estate | 2025 |
| Maita Homes CIC | Public administration | 2023 |
| Major Travel PLC | Administrative & support | 1984 |
| Make Freedom Ring Ltd | Other services | 2024 |
| Make My House Warmer Ltd | Construction | 2025 |
| Make Relevant Group Limited | Professional & scientific | 2022 |
| Make Time Count Enterprises Ltd | Construction | 2025 |
| Make-Up by JO Ltd | Other services | 2011 |
| Malbe Limited | Manufacturing | 2008 |
| Maleni Limited | Wholesale & retail | 2006 |
| Malik Trading (UK) Limited | Wholesale & retail | 2015 |
| MAM Education Limited | Extraterritorial | 2020 |
| MAM Group Limited | Financial services | 2016 |
| Mama MIA Richmond Ltd | Hospitality | 2024 |
| Mamhead Capital Ltd | Financial services | 2024 |
| MAN Asset Management Limited | Financial services | 2024 |
| Manasian & Co Limited | Administrative & support | 2009 |
| Manor Cottage Care Limited | Health & social care | 2003 |
| Manor Plastering Artistry Limited | Construction | 2025 |
| Manor Road (Richmond) Management Company Limited | Households | 2004 |
| Manual Therapy Ltd | Health & social care | 2020 |
| Manustech Ltd | Information & communication | 2018 |
| MAP Insight Limited | Information & communication | 2013 |
| Mapadamia Ltd | Real estate | 2023 |
| Mapesbury Road Limited | Real estate | 2016 |
| Maran Limited | Professional & scientific | 2014 |
| Maranda Court Investments Limited | Real estate | 2018 |
| Marc Baker Limited | Information & communication | 2009 |
| Marcar Holdings Limited | Financial services | 1956 |
| Marcar Steel & Engineering Limited | Wholesale & retail | 1951 |