| M&J Controls Limited | Construction | 2026 |
| M&K Holden Investments Ltd | Financial services | 2025 |
| M&R Delivery Services Limited | Transport & logistics | 2005 |
| M.A.P Commercial Ltd | Construction | 2022 |
| M.Abdeen Radiology Limited | Health & social care | 2016 |
| M.C. Harding Design Services Limited | Professional & scientific | 1981 |
| M.D. Diagnostics Limited | Manufacturing | 2008 |
| M.I.O Ltd | Wholesale & retail | 2018 |
| M.J Lewis Properties Ltd | Real estate | 2024 |
| M.N & Sons Enterprises Ltd | Hospitality | 2017 |
| M.P.Fire Limited | Construction | 2009 |
| M.P.S Electrical (Kent) Limited | Construction | 2012 |
| M.S. Michael & Co. (Holdings) Limited | Professional & scientific | 1960 |
| M.S.Maintenance Ltd | Other services | 2004 |
| M.S.Michael & Co. Limited | Manufacturing | 1932 |
| M19 Capital Limited | Financial services | 2024 |
| M19 Holding Limited | Financial services | 2024 |
| M2 Exhibition Services Ltd | Administrative & support | 2024 |
| M25 Haulage Limited | Construction | 2023 |
| M8 Logistics Ltd | Transport & logistics | 2025 |
| M8 Motors Ltd | Wholesale & retail | 2024 |
| M8 Property Services Ltd | Construction | 2024 |
| MA General Building Ltd | Construction | 2024 |
| MA Nursery Ltd | Health & social care | 2024 |
| Maade Limited | Other services | 2013 |
| Maajaan Limited | Health & social care | 2019 |
| Maan Educate Ltd | Administrative & support | 2025 |
| Maaso Services Ltd | Transport & logistics | 2024 |
| Mablevi UK Ltd | Wholesale & retail | 2021 |
| MAC Flooring Designs Ltd | Construction | 2025 |
| Mach 1 Motorcycles Ltd | Wholesale & retail | 2023 |
| MACH1 Automotive Ltd | Wholesale & retail | 2017 |
| Machar Limited | Professional & scientific | 2002 |
| Mackard Services Ltd | Construction | 2020 |
| Mackinlay Ltd | Real estate | 2009 |
| Mactire Associates Limited | Professional & scientific | 2020 |
| MAD Jack's Developments Limited | Real estate | 2023 |
| Madals Limited | Other services | 2013 |
| Maddison Spencer Properties Ltd | Real estate | 2018 |
| Maddysnails Ltd | Wholesale & retail | 2025 |
| Madenta International Ltd | Health & social care | 2018 |
| Madigold Ltd | Professional & scientific | 2025 |
| Madway Brewing Company Ltd | Manufacturing | 2020 |
| Mafin Properties Limited | Real estate | 2024 |
| Magee Mechanical Services Ltd | Construction | 2019 |
| Magenta Flair Limited | Manufacturing | 2006 |
| Magnalia Limited | Real estate | 2025 |
| Magnolija Ltd | Wholesale & retail | 2025 |
| Magnum Land Limited | Real estate | 2014 |
| Magnus Lumen Ltd | Real estate | 2024 |
| Magpie Property Glasgow Ltd | Real estate | 2026 |
| Magstone Homes Ltd | Real estate | 2025 |
| Maha House Ltd | Real estate | 2020 |
| Mahogany Homes Limited | Real estate | 2018 |
| Mahrusmarsad Ltd | Hospitality | 2025 |
| Maid My Day Ltd | Administrative & support | 2025 |
| Maidenside Ltd | Administrative & support | 2025 |
| Main Street Leasing Limited | Wholesale & retail | 2020 |
| Maingate Electrical Services Ltd | Manufacturing | 2012 |
| Mainsail (Trading & Shipping) Limited | Professional & scientific | 2019 |
| Maison Nuovo Ltd | Other services | 2025 |
| Maiworld Beauty Place Ltd | Other services | 2025 |
| Majestic Essences Ltd | Wholesale & retail | 2023 |
| Majestic Ventures Ltd | Manufacturing | 2004 |
| Major Distribution Support Limited | Transport & logistics | 2022 |
| Major Heights Ltd | Transport & logistics | 2019 |
| MAK Sale Ltd | Manufacturing | 2010 |
| Make Medway CIC | Education | 2025 |
| Make Room Loft Conversions Ltd | Construction | 2016 |
| Make Space ETC Ltd | Real estate | 2013 |
| Malcolm Aitkin Ltd | Administrative & support | 2024 |
| Malikfadez UK Ltd | Other services | 2024 |
| Mallisons Ltd | Real estate | 2025 |
| Maltom Investment Company Limited | Real estate | 2022 |
| Malusa Limited | Public administration | 2023 |
| Mama Airlines Limited | Transport & logistics | 2001 |
| Mama Awon Boys Limited | Wholesale & retail | 2023 |
| MAN Carpentry 66 Ltd | Construction | 2025 |
| Mana Holdings Ltd | Other services | 2017 |
| Mana Search Limited | Administrative & support | 2022 |
| Management for Health Limited | Administrative & support | 2010 |
| Mangroove Limited | Hospitality | 2024 |
| Manhattan M&E Ltd | Construction | 2022 |
| Manitou Solutions Ltd | Professional & scientific | 2024 |
| Manor House Financial Solutions Limited | Financial services | 2026 |
| Manor Mews (Chatham) Limited | Real estate | 1998 |
| Manston Cargo Limited | Transport & logistics | 2020 |
| Manta Gray Ltd | Hospitality | 2023 |
| Manticore Software Ltd | Information & communication | 2017 |
| Mapa Trading Limited | Wholesale & retail | 2023 |
| Maple North Ltd | Real estate | 2025 |
| MAQ Enterprises (UK) Ltd | Hospitality | 2015 |
| Marathon Wealth Management Ltd | Administrative & support | 2021 |
| Marchant Motorsport Ltd | Manufacturing | 2025 |
| Marcin Lyzak Ltd | Extraterritorial | 2018 |
| Mardell Group Limited | Financial services | 2025 |
| Mardell Properties Limited | Construction | 2025 |
| Mardell Ventures Limited | Wholesale & retail | 2025 |
| Mare Monte Limited | Wholesale & retail | 2020 |
| Marez Brasserie Ltd | Hospitality | 2020 |