| Maidenhead Specsavers Limited | Wholesale & retail | 1996 |
| Maidenhead Visionplus Limited | Wholesale & retail | 1996 |
| Maidstone Domi Audiology Specsavers Limited | Wholesale & retail | 2024 |
| Maidstone Domiciliary Specsavers Limited | Wholesale & retail | 2018 |
| Maidstone Specsavers Hearcare Limited | Wholesale & retail | 2006 |
| Maidstone Specsavers Limited | Wholesale & retail | 1992 |
| Maidstone Visionplus Limited | Wholesale & retail | 2001 |
| Mailock Corporate Trustee Limited | Administrative & support | 2017 |
| Mailock Limited | Administrative & support | 2006 |
| Main AIM Global Ltd | Professional & scientific | 2003 |
| Maison Royale Ltd | Real estate | 2026 |
| Maitom Limited | Health & social care | 2023 |
| MAJ Properties & Accommodations Limited | Hospitality | 2025 |
| Majengo Ltd. | Construction | 2009 |
| Majr Analysis Limited | Information & communication | 2016 |
| Maladee Properties Limited | Real estate | 2024 |
| Maldon Specsavers Limited | Wholesale & retail | 2010 |
| Males Construction Limited | Construction | 2022 |
| Males Holdings Limited | Financial services | 2022 |
| Males Technical Fabrications Limited | Other services | 2006 |
| Malleus Communications Holdings Limited | Financial services | 2026 |
| Malleus Communications Limited | Professional & scientific | 2026 |
| Malvern Retail Park Specsavers Limited | Wholesale & retail | 2017 |
| Malvern Specsavers Hearcare Limited | Wholesale & retail | 2025 |
| Malvrn Developments Ltd | Real estate | 2025 |
| Mamawu Limited | Hospitality | 2020 |
| Manaba Ltd | Information & communication | 2022 |
| Manchester 2 Domiciliary Specsavers Limited | Wholesale & retail | 2013 |
| Manchester Domi Audiology Specsavers Limited | Wholesale & retail | 2023 |
| Manchester Fort Specsavers Limited | Wholesale & retail | 2012 |
| Manchester Specsavers Hearcare Limited | Wholesale & retail | 2007 |
| Manchester Therapy Ltd | Health & social care | 2025 |
| Manchester West Newmedica Limited | Health & social care | 2024 |
| Manchun Limited | Wholesale & retail | 2023 |
| Mandaco 516 Limited | Manufacturing | 2007 |
| Manformes Limited | Administrative & support | 2013 |
| Mann Mortgages Limited | Financial services | 2017 |
| Mann Real Estate Limited | Real estate | 2016 |
| Manser Heating & Plumbing Ltd | Construction | 2024 |
| Mansfield Nottingham Specsavers Limited | Wholesale & retail | 2018 |
| Mansfield Specsavers Hearcare Limited | Wholesale & retail | 2019 |
| Mansfield Specsavers Limited | Wholesale & retail | 1992 |
| Mansfield Visionplus Limited | Wholesale & retail | 1992 |
| Mansion House Publications Limited | Professional & scientific | 2013 |
| Manta Services Limited | Construction | 2016 |
| Manu Online Limited | Administrative & support | 2010 |
| Many Skips Ltd | Wholesale & retail | 2025 |
| Maple Business Consultants Limited | Administrative & support | 1990 |
| Maple Grove Homes Limited | Construction | 2023 |
| Maple Lodge Estates Limited | Real estate | 2021 |
| Maple Maple Strawberry Ltd | Hospitality | 2023 |
| Marc Jones Consultancy Limited | Construction | 2019 |
| March on Stress Limited | Health & social care | 2003 |
| March Specsavers Hearcare Limited | Wholesale & retail | 2026 |
| March Specsavers Limited | Wholesale & retail | 2011 |
| March Timber Limited | Wholesale & retail | 2021 |
| Marga Limited | Wholesale & retail | 2009 |
| Margate Specsavers Limited | Wholesale & retail | 1992 |
| Margate Visionplus Limited | Wholesale & retail | 1992 |
| Margaux MAE Bridal Limited | Wholesale & retail | 2021 |
| Margolis Silver Limited | Wholesale & retail | 2006 |
| Margot Jewellery London Ltd | Wholesale & retail | 2012 |
| Margus Properties Ltd | Real estate | 2023 |
| Maria B Aesthetics Limited | Other services | 2025 |
| Marielianne Design Limited | Professional & scientific | 2012 |
| Marik Services Limited | Administrative & support | 2013 |
| Marina Cars Port Solent Ltd | Transport & logistics | 2018 |
| Marina Properties Limited | Real estate | 2016 |
| Marine and Aviation Limited | Administrative & support | 2007 |
| Marine Concepts Limited | Manufacturing | 1998 |
| Marine Dredging Services (UK) Ltd | Construction | 2025 |
| Marine Gate Management Company (Southsea) Limited | Extraterritorial | 1994 |
| Marine Marketing Ltd | Professional & scientific | 2023 |
| Marine Services Top Co Limited | Financial services | 2022 |
| Mariner Trading Limited | Wholesale & retail | 2012 |
| Mariners Quay Limited | Hospitality | 2017 |
| Marinus Vessels Ltd | Professional & scientific | 2024 |
| MARIO23 Ltd | Transport & logistics | 2016 |
| Maritime Aviation Support Training (Mast) Consultancy Limited | Professional & scientific | 2013 |
| Maritime Film Limited | Information & communication | 2024 |
| Marjoram Properties Limited | Real estate | 2023 |
| Mark Ballard Limited | Construction | 2001 |
| Mark Jones Q.S. Limited | Professional & scientific | 2015 |
| Mark Mcguinness Consulting Limited | Professional & scientific | 2024 |
| Mark Moore Consultancy Limited | Professional & scientific | 2023 |
| Mark Watts Decorating & Home Improvements Ltd | Construction | 2025 |
| Market Drayton Specsavers Limited | Wholesale & retail | 2008 |
| Market Drayton Visionplus Limited | Wholesale & retail | 2008 |
| Market Harborough Specsavers Limited | Wholesale & retail | 2002 |
| Marlborough Court Chandlers Ford Ltd | Households | 2018 |
| Marlborough Specsavers Limited | Wholesale & retail | 2009 |
| Marlow Specsavers Limited | Wholesale & retail | 2019 |
| Marmalade Investments Ltd | Real estate | 2024 |
| Marmich Healthcare Ltd | Health & social care | 2023 |
| Marmion Holdings Ltd | Professional & scientific | 2021 |
| Maronway Limited | Construction | 2012 |
| Marpac Limited | Administrative & support | 1994 |
| Marquees by Nixon Limited | Administrative & support | 2015 |
| Marshall Whittaker Real Estate Ltd. | Real estate | 2020 |
| Marshall-Astley Motors Limited | Wholesale & retail | 2025 |