| M and M Pipeworks Ltd | Construction | 2019 |
| M and P Singh Ltd | Wholesale & retail | 2025 |
| M Condron Ltd | Arts & recreation | 2010 |
| M D Alderton Limited | Construction | 2006 |
| M Hall Holdings Limited | Financial services | 2010 |
| M Hall Services Limited | Construction | 2010 |
| M K & Daughters Rentals Ltd | Administrative & support | 2016 |
| M P Richardson Limited | Construction | 2003 |
| M R Hart Carpentry Limited | Construction | 2010 |
| M T Electrical (Essex) Limited | Construction | 2006 |
| M&Ak Consultancy UK Ltd | Transport & logistics | 2012 |
| M&G Concepts Limited | Information & communication | 2011 |
| M2 Print Limited | Manufacturing | 2014 |
| M2R Auto Services Ltd | Wholesale & retail | 2023 |
| M2R Motorsport Ltd | Wholesale & retail | 2020 |
| M2U Ltd | Administrative & support | 2017 |
| MA Carpentry and Maintenance Ltd | Construction | 2019 |
| MA Divane Estates Ltd | Real estate | 2019 |
| MA Divane Holdings Limited | Financial services | 2019 |
| MA Divane Plant Limited | Administrative & support | 2019 |
| MA Roofing Solutions Ltd | Construction | 2024 |
| Macbac Limited | Real estate | 1996 |
| Macweb Accounting Ltd | Professional & scientific | 2020 |
| Madocs Engineering Ltd | Manufacturing | 2010 |
| Magic Part Ltd | Information & communication | 2024 |
| Magnetic Brands Limited | Wholesale & retail | 2016 |
| Magnolia Education UK Limited | Education | 2021 |
| Magpie Tech Consulting Ltd | Professional & scientific | 2024 |
| Maid Marion's Cleaning Services Limited | Other services | 2013 |
| Maids in Black Ltd | Administrative & support | 2022 |
| Main Event Wedding Shows Ltd | Other services | 2011 |
| Mainline Contractors Limited | Construction | 1987 |
| Maiso Products Ltd | Wholesale & retail | 2023 |
| Maison Belle Collective Ltd | Wholesale & retail | 2026 |
| Majestic Domestic Limited | Administrative & support | 2016 |
| Majesty House Limited | Information & communication | 2006 |
| Major Electrical Installations Limited | Construction | 2012 |
| Make ALL the Things Ltd | Arts & recreation | 2022 |
| MAL Car Valeting Ltd | Other services | 2016 |
| Malachite Wellness Group Limited | Wholesale & retail | 2024 |
| Maldon Trading Ideas Limited | Real estate | 2015 |
| Maldon Trading Ideas Retail Limited | Wholesale & retail | 2019 |
| Mali K9 Security Services Ltd | Administrative & support | 2024 |
| Maltings Management Company (Braintree) NO.2 Limited | Real estate | 2001 |
| Mammoth Bathrooms Limited | Construction | 2024 |
| MAN Cave Media Limited | Information & communication | 2017 |
| Managed Water Services Limited | Professional & scientific | 2005 |
| Management and Consultancy Services Limited | Construction | 2012 |
| Manchester Housing Limited | Real estate | 2019 |
| Manco Property Limited | Real estate | 2020 |
| Mandy Transport Ltd | Transport & logistics | 2025 |
| Mannionabroad Ltd | Education | 2026 |
| Mannionlets Ltd | Real estate | 2020 |
| Manor Payments Ltd | Information & communication | 2021 |
| Mansion Building Ltd | Hospitality | 2024 |
| Mansion Functions Ltd | Hospitality | 2023 |
| Mansion Hotel & Bar Ltd | Hospitality | 2023 |
| Mantis Simulators Ltd | Manufacturing | 2022 |
| Marabout Security Sevices Ltd | Administrative & support | 2025 |
| Marange Care Ltd | Health & social care | 2019 |
| Mareve Engineering Support Limited | Professional & scientific | 2017 |
| Margate Seaview Ltd | Real estate | 2019 |
| Mark Hawthorne GAS Service Engineer Limited | Construction | 2015 |
| Mark Liell & SON LLP | | 2001 |
| Mark Liell (Residential) Limited | Extraterritorial | 1998 |
| Mark on the Move Ltd | Water & waste | 2026 |
| Mark Whittle Roofing Limited | Construction | 2024 |
| Markcaz Rentals Limited | Real estate | 2023 |
| Market 36 Recruitment Limited | Administrative & support | 2017 |
| Marksman Finance Ltd | Financial services | 2018 |
| Markwell Wood Management Limited | Households | 1987 |
| Marr Technology Consulting Limited | Information & communication | 2015 |
| Marsh Property Solutions Limited | Real estate | 2022 |
| Martin Image Processing Limited | Information & communication | 2004 |
| Marvel HCL Motorsport Ltd | Administrative & support | 2022 |
| Marvel HCL Properties Ltd | Real estate | 2021 |
| Marvel Healthcare Construction Ltd | Construction | 2018 |
| Marvellous Glow Ltd | Administrative & support | 2016 |
| Marven Horrex-Barrett Ltd | Hospitality | 2026 |
| Masefield 168 Ltd | Hospitality | 2021 |
| Mason Bespoke Construction Ltd | Construction | 2021 |
| Mason Carpentry & Building Services Ltd | Construction | 2018 |
| Master Brickbros Ltd | Wholesale & retail | 2022 |
| Master Cutters (Ashford) Limited | Other services | 2001 |
| Master Cutters (Salons) Limited | Other services | 2006 |
| Master Cutters (Tenterden) Limited | Professional & scientific | 2001 |
| Matex EMS Limited | Construction | 2024 |
| Matrix Risk Solutions Limited | Administrative & support | 2021 |
| Matt Brinkley Inspiring Fitness Limited | Other services | 2017 |
| Matthew Pugh Limited | Professional & scientific | 2013 |
| Mauldeth West Ltd | Arts & recreation | 2022 |
| Maunds Farm Residents Association Limited | Households | 1987 |
| Maxed IT Limited | Other services | 2007 |
| Maxheadroom Ltd | Other services | 2023 |
| MAY Developments (Herts) Ltd | Construction | 2017 |
| MAY Homes Limited | Construction | 2004 |
| MAY Investment Properties Limited | Real estate | 2020 |
| Maydale Consulting Ltd | Professional & scientific | 2015 |
| Mayhem Paintball Limited | Extraterritorial | 2012 |
| Mayra Homes Ltd | Real estate | 2023 |