| MB Steel Solutions Limited | Professional & scientific | 2016 |
| MBD Site Services Ltd | Construction | 2026 |
| MBS Group U.K. Ltd | Construction | 2012 |
| MC & RE Properties Ltd | Construction | 2013 |
| MC Group (Holdings) Ltd | Professional & scientific | 2002 |
| Mc&C Limited | Wholesale & retail | 2004 |
| Mcdowell Mews Management Company Limited | Households | 2019 |
| Mcginley & Sons Commercials Ltd | Wholesale & retail | 2022 |
| Mcginley Properties & Rental Ltd. | Real estate | 2023 |
| Mcguiness & Farrow Ltd | Construction | 2020 |
| MCK Utility Services Limited | Energy | 2025 |
| Mcnab Plumbing and Heating Solutions Limited | Construction | 2018 |
| MD Landscapes (Anglia) Limited | Administrative & support | 2007 |
| MD Technical (Essex) Limited | Information & communication | 2019 |
| MDB Industries Ltd | Transport & logistics | 2024 |
| MDD Consultancy Ltd | Professional & scientific | 2026 |
| MDG (UK) Limited | Construction | 2006 |
| MDG Complete Solutions Limited | Construction | 2006 |
| MDH Cladding Limited | Construction | 2017 |
| Mdhudson Limited | Other services | 2021 |
| ME 1 Enterprises Ltd | Wholesale & retail | 2022 |
| Meadow Croft Properties Limited | Professional & scientific | 2025 |
| Meadow Hedges & Woods Limited | Other services | 1990 |
| Mectech Data Systems Limited | Information & communication | 2010 |
| Mectech Limited | Wholesale & retail | 2005 |
| Mectech Motorsport Limited | Arts & recreation | 2010 |
| Mectech Services (Sales) Limited | Wholesale & retail | 1998 |
| Media in Mind Group Limited | Professional & scientific | 2010 |
| Medical Device Management Holdings Limited | Financial services | 2021 |
| Medical Device Management Limited | Manufacturing | 2000 |
| Medical Response Solutions Limited | Health & social care | 2013 |
| Medsync Limited | Education | 2014 |
| Meens Construction Ltd | Construction | 2025 |
| Meet My Muse Ltd | Information & communication | 2026 |
| Meetings Industry Meeting Needs | Professional & scientific | 2004 |
| Megzie Healthcare Limited | Public administration | 2022 |
| MEN2MENTALITY Ltd | Administrative & support | 2024 |
| Meridian Commercial Insurance Services Ltd | Financial services | 2001 |
| Mersea Holidays Limited | Hospitality | 2015 |
| Metet Ltd | Wholesale & retail | 2019 |
| Metro Repairs Limited | Manufacturing | 2010 |
| Metrul Limited | Hospitality | 2023 |
| Mfrm Consulting Limited | Information & communication | 2024 |
| MGP Building Services Ltd | Professional & scientific | 2024 |
| MHB Constructions Ltd | Construction | 2023 |
| MHF Properties Ltd | Real estate | 2016 |
| Michael Laurence Limited | Construction | 2014 |
| Michaels Lettings & Property Management Braintree Ltd | Real estate | 2022 |
| Mickcab Company Limited | Transport & logistics | 2009 |
| Microbiome Bank Ltd | Health & social care | 2021 |
| Micromax Ltd | Other services | 2018 |
| Micromech Employee Benefit Trustee Limited | Extraterritorial | 2006 |
| Micromech Holdings Limited | Manufacturing | 1994 |
| Micromech Limited | Manufacturing | 1981 |
| Micromech Systems Limited | Manufacturing | 1991 |
| Midnightinkdesign Studio Ltd | Professional & scientific | 2026 |
| Mighty Brickwork Ltd | Construction | 2018 |
| Mihaialuminiumtech Limited | Manufacturing | 2023 |
| Mihan & Co Ltd | Wholesale & retail | 2017 |
| Mike Boboe Limited | Information & communication | 2020 |
| Mike Porter Limited | Agriculture & fishing | 2015 |
| Mikeys on the Drive Ltd | Administrative & support | 2025 |
| Mill Range (Black Notley) Management Company Limited | Construction | 2015 |
| Millar Investments Ltd | Professional & scientific | 2009 |
| Millar Property Consultancy Ltd | Construction | 2019 |
| Milleniumassociates (UK) Limited | Professional & scientific | 2008 |
| Millennium Veterinary Practice Limited | Professional & scientific | 2010 |
| Miller & Meadow Limited | Wholesale & retail | 2025 |
| Miller's Garden Services Limited | Construction | 2013 |
| Millfields Cattery Limited | Professional & scientific | 2018 |
| Millside Floors Limited | Construction | 2013 |
| Mindful Mortgage Solutions Limited | Financial services | 2026 |
| Mini Affair Limited | Real estate | 2007 |
| Mini Munchkins Party Hire Limited | Arts & recreation | 2021 |
| Miracle Aligner UK Limited | Health & social care | 2021 |
| Miracle RUM Company Ltd | Wholesale & retail | 2025 |
| Mirecc Ltd | Professional & scientific | 2019 |
| Miss Spirit London Limited | Other services | 2021 |
| Mitchell's Kitchens (2019) Ltd | Wholesale & retail | 2021 |
| Mixar Ltd | Professional & scientific | 2018 |
| MJ Transport Logistics Ltd | Transport & logistics | 2023 |
| MJC Contractors Limited | Construction | 2007 |
| MJD Property Management Ltd | Real estate | 2015 |
| MJL Displays Ltd | Other services | 2018 |
| MJM Broadcast Limited | Construction | 2012 |
| MJS Hospitality Essex Ltd | Hospitality | 2023 |
| MJS Sports Ltd | Wholesale & retail | 2015 |
| MK Automotive Limited | Manufacturing | 2016 |
| MK Performance Ltd | Wholesale & retail | 2021 |
| MK Telecomms Ltd | Construction | 2025 |
| MKB Comms Limited | Information & communication | 2014 |
| MLM Golf Ltd | Arts & recreation | 2026 |
| MLS (Overseas) Limited | Administrative & support | 1999 |
| MMI Electrical Services (UK) Limited | Construction | 2013 |
| Mmjc Properties Limited | Real estate | 2013 |
| MNA Itech Limited | Wholesale & retail | 2017 |
| MNE Ventures Ltd | Other services | 2016 |
| Moate Properties Limited | Real estate | 2025 |
| Mobigo-Uk Limited | Wholesale & retail | 2025 |
| Mobile Mechanic Solutions Ltd | Wholesale & retail | 2025 |