| Lyndhurst Estate Management Limited | Professional & scientific | 1997 |
| Lyndhurst Financial Management Limited | Financial services | 1992 |
| Lyndtree Associates Limited | Professional & scientific | 2017 |
| Lynwood Property Management Company Limited | Households | 1996 |
| Lysander Property Limited | Real estate | 2023 |
| M & T Group of Companies Ltd | Financial services | 2019 |
| M Martin Project Design and Build Limited | Construction | 2013 |
| M&M Investment and Development LLP | | 2023 |
| M&T Consulting Ltd | Professional & scientific | 2019 |
| M.M.A Essex Electrical Limited | Manufacturing | 2025 |
| M2 Tax and Accountancy Ltd | Professional & scientific | 2010 |
| MAA Consult Limited | Other services | 2021 |
| Macadamia Ltd | Manufacturing | 2013 |
| Macpro Design & Print Limited | Manufacturing | 2003 |
| Mactech Autos Ltd | Wholesale & retail | 2025 |
| Maga Oshin Ltd | Real estate | 2022 |
| Magellan 2000 Ltd | Professional & scientific | 2010 |
| Maginn Partnership Ltd | Households | 2018 |
| Magnolia Sun Ltd | Information & communication | 2026 |
| Mahogany Growth Limited | Wholesale & retail | 2026 |
| Maidment Judd Ltd | Professional & scientific | 2010 |
| Majestic Consultancy Services Ltd | Wholesale & retail | 2024 |
| Majestic Properties Incorporated Limited | Real estate | 2026 |
| Majestic Solutions Services Limited | Water & waste | 2025 |
| Makecloud Limited | Information & communication | 2007 |
| Makeit Dogs Limited | Agriculture & fishing | 2019 |
| Makeitso Consultants Ltd | Information & communication | 2019 |
| Malachite Films Limited | Information & communication | 2013 |
| Malbec Close Management Company Limited | Administrative & support | 2009 |
| Mallard Mews Management Company Limited | Administrative & support | 2006 |
| Malvern-I Ltd | Professional & scientific | 2025 |
| Mamore Research and Innovation Limited | Professional & scientific | 2021 |
| MAN for the JOB Limited | Construction | 2023 |
| Manacal Limited | Education | 2013 |
| Management Training Solutions Limited | Professional & scientific | 1997 |
| Mander Properties Ltd | Real estate | 2025 |
| Mandrake Verulam Limited | Professional & scientific | 2014 |
| Manlando Limited | Real estate | 2025 |
| Manlee Ltd | Real estate | 2010 |
| Manor Urology Ltd | Health & social care | 2015 |
| Manorseal Limited | Real estate | 2000 |
| Mansfield Bowling CLUB(1920)LTD(THE) | Arts & recreation | 1920 |
| Mantatech Software Limited | Information & communication | 2021 |
| Maple & Field Limited | Construction | 2025 |
| Maple Ridge Homes Limited | Construction | 2018 |
| Mardall Securities | | 2000 |
| Marian Browne Exhibitions Ltd | Administrative & support | 2023 |
| Marian Lapping Vintage Limited | Wholesale & retail | 2021 |
| Maricas Properties Limited | Real estate | 2017 |
| Marie Gascoigne Associates Limited | Professional & scientific | 2007 |
| Mark Laurence Investments Limited | Financial services | 2015 |
| Mark Wittich Limited | Arts & recreation | 2005 |
| Marlborough Information Services Limited | Education | 2005 |
| Marlow Anaesthesia Ltd | Health & social care | 2023 |
| Marshall Carpentry Services Ltd | Construction | 2015 |
| MAS Managerial Services Ltd | Administrative & support | 2024 |
| Mask Design Studio Ltd | Professional & scientific | 2019 |
| Matanga Solutions Ltd | Professional & scientific | 2018 |
| Match Property Investments Limited | Real estate | 2025 |
| Matchday TV Ltd | Information & communication | 2019 |
| Mathru Properties Limited | Real estate | 2025 |
| Matrix Moving Solutions Limited | Transport & logistics | 2014 |
| Matte Development and Design Ltd | Construction | 2020 |
| Matthew J Rickard Holdings Ltd | Real estate | 2026 |
| Maulden Renewable Tech Ltd | Construction | 2025 |
| MAX Logs Consulting Ltd | Professional & scientific | 2019 |
| Maxi Logistics Services Ltd | Wholesale & retail | 2021 |
| Maylin Ltd | Extraterritorial | 2013 |
| MBC Services Ltd | Professional & scientific | 2022 |
| MBD Bookkeeping and Payroll Services Limited | Professional & scientific | 2020 |
| MBK Consulting Limited | Professional & scientific | 2023 |
| MBW Technologies Ltd | Information & communication | 2022 |
| MC Modelling Limited | Professional & scientific | 2024 |
| MC76 Consulting Limited | Information & communication | 2025 |
| MCC IT Tutors Limited | Transport & logistics | 2018 |
| Mccarty London Limited | Administrative & support | 2019 |
| Mcdonagh & Sons Limited | Real estate | 2020 |
| Mcdonagh Properties Limited | Real estate | 2017 |
| Mchd Investments Limited | Professional & scientific | 2012 |
| Mcshc Limited | Financial services | 2013 |
| Mcveigh Engineering Services Ltd | Professional & scientific | 2019 |
| Mdcook Consulting Ltd | Professional & scientific | 2024 |
| Me&Fa Design Limited | Manufacturing | 2019 |
| Mead Well Services Ltd | Construction | 2019 |
| Meadowview Care Home Limited | Health & social care | 2026 |
| Meat Feast Co. Ltd | Manufacturing | 2020 |
| MED SCI International Limited | Professional & scientific | 1993 |
| Medhome UK Ltd | Professional & scientific | 2020 |
| Media 38 Ltd | Information & communication | 2026 |
| Medicaana Ltd | Wholesale & retail | 2026 |
| Medicalsec Harpenden Limited | Administrative & support | 2011 |
| Medico Health Limited | Wholesale & retail | 2015 |
| Medium Rare N.V. / TGP Europe Limited | Information & communication | 2024 |
| Melin Consultancy Limited | Professional & scientific | 2007 |
| Melioro Group Limited | Professional & scientific | 2018 |
| Melissa Phillips Limited | Health & social care | 2022 |
| Meller Consulting Limited | Professional & scientific | 2018 |
| Mellow Pages Limited | Information & communication | 2021 |
| Melt the Icebergs Ltd | Professional & scientific | 2021 |
| Memorial Hospitals Ltd | Health & social care | 2024 |