| Magnus Servizi Globali Integrati Ltd | Administrative & support | 2017 |
| Magrini Procurement & Business Development Ltd | Professional & scientific | 2018 |
| Mahshu Ltd | Other services | 2023 |
| Mahveen Ltd | Real estate | 2025 |
| Mailgold Limited | Households | 1983 |
| Main Contracts Ltd | Construction | 2009 |
| Mainstream Marketing UK Ltd. | Professional & scientific | 1999 |
| Mairie Rose Limited | Arts & recreation | 2012 |
| Maison AMI Ltd | Construction | 2022 |
| Maison Mayam Limited | Information & communication | 2025 |
| Majorlaw Limited | Professional & scientific | 2013 |
| Make a Dent Limited | Professional & scientific | 2016 |
| Make a Difference Leadership Foundation | Health & social care | 2008 |
| Make Engineering Solutions Limited | Manufacturing | 2014 |
| Malfunction Limited | Information & communication | 2024 |
| Maltby Property Limited | Construction | 2010 |
| Mamex Invest Limited | Financial services | 2025 |
| Mamex West Limited | Real estate | 2008 |
| Managed Energy Solutions Limited | Administrative & support | 2012 |
| Manathra Limited | Real estate | 2023 |
| Manchester Factoring Limited | Financial services | 2023 |
| Mandago Limited | Professional & scientific | 1982 |
| Mandira Limited | Wholesale & retail | 2009 |
| Mandy Stevens Consulting Limited | Health & social care | 2015 |
| Mango Property Group Ltd | Real estate | 2025 |
| Manhan Limited | Real estate | 2017 |
| Mani Matters Limited | Professional & scientific | 2019 |
| MANJOBARS2 Limited | Hospitality | 2023 |
| Manning & Sons Landscaping Ltd | Professional & scientific | 2023 |
| Manor Classics Limited | Wholesale & retail | 2014 |
| Manor Down Limited | Financial services | 2021 |
| Manor Farm Barns Holdings Ltd | Construction | 2019 |
| Manor Green Management Company Limited | Households | 1987 |
| Manor Landscapes Limited | Professional & scientific | 2008 |
| Mans 2020 Ltd | Real estate | 2020 |
| Mansio Furniture Ltd | Wholesale & retail | 2026 |
| Mansion House Financial Planning Limited | Financial services | 2014 |
| Manta Marine Services Ltd | Construction | 2022 |
| Mantisonix Ltd | Water & waste | 2024 |
| Maori Park Estate Limited | Households | 2018 |
| Mapaguas Limited | Professional & scientific | 2018 |
| Mapel Global Limited | Professional & scientific | 2019 |
| Maple Gate Investments Limited | Construction | 2020 |
| Mapstar Limited | Information & communication | 2004 |
| Marble & Mint Ltd | Administrative & support | 2025 |
| Marble Arch Schools Limited | Education | 2025 |
| Marble Tops Ltd | Other services | 2017 |
| Marcus Crassus International Ltd | Wholesale & retail | 2018 |
| Margrave Solicitors LLP | | 2010 |
| Marianita Alma Goncalves Ltd | Health & social care | 2023 |
| Marine Masterclass Ltd | Administrative & support | 2016 |
| Marine Technical Services Limited | Extraterritorial | 1987 |
| Marion Manuel Limited | Wholesale & retail | 2025 |
| Mark & Partners Limited | Professional & scientific | 2020 |
| Mark Bauer Ltd | Extraterritorial | 2024 |
| Mark Collins (Guildford) Limited | Real estate | 2019 |
| Mark Palmer Associates Limited | Other services | 2011 |
| Mark Randall Associates Limited | Agriculture & fishing | 2004 |
| Marker Pro Ltd | Construction | 2025 |
| Marker Services Ltd | Construction | 2025 |
| Marlin Building Services Limited | Administrative & support | 2014 |
| Marmatt Building Services Ltd | Construction | 2019 |
| Marsdens C.S. Limited | Real estate | 1996 |
| Martello Property Limited | Construction | 2004 |
| Marti Clearpath Ltd | Professional & scientific | 2025 |
| Martin & Co Painting and Decorating Ltd | Construction | 2023 |
| Martin Cleaning Ltd | Administrative & support | 2022 |
| Martin Watkins Design Ltd | Arts & recreation | 2015 |
| Martin-Christian Kent Consulting Ltd | Administrative & support | 2018 |
| Marulyan Limited | Real estate | 2017 |
| Mary & Jayne Ltd | Wholesale & retail | 2021 |
| Maryna Rusalovych Ltd | Other services | 2023 |
| Mashpi Limited | Professional & scientific | 2025 |
| Maslin Solicitors Limited | Professional & scientific | 2016 |
| Mason Stowood Ltd | Construction | 2012 |
| Mason Voller Limited | Construction | 1992 |
| Masson Consulting Limited | Information & communication | 2015 |
| Masterguest Ltd | Professional & scientific | 2021 |
| Mati Carbon Limited | Professional & scientific | 2026 |
| Mati Investments Ltd | Construction | 2025 |
| Mati Spaces Ltd | Real estate | 2025 |
| Matilda & Co. Limited | Administrative & support | 2025 |
| Matrix Search Limited | Administrative & support | 2022 |
| Matthew Edward Solutions Limited | Professional & scientific | 2025 |
| Matthew Foreman Research Limited | Arts & recreation | 2022 |
| Matthew Sharp Plumbing and Heating Limited | Construction | 2022 |
| Maui JIM UK Limited | Administrative & support | 2002 |
| Mauricejvrconsulting Ltd | Administrative & support | 2022 |
| Maven Consulting Services Ltd | Arts & recreation | 2012 |
| Maven Support Services Ltd | Administrative & support | 2019 |
| Maverick Marketing Services Ltd | Professional & scientific | 2019 |
| Maverickmc Ltd | Professional & scientific | 2023 |
| Mavericks Barber Shop Ltd | Other services | 2024 |
| Mavericks Barbershop Beyond Gravity Ltd. | Other services | 2024 |
| MAW Salons Limited | Other services | 2002 |
| MAX 500 Ltd | Wholesale & retail | 2015 |
| MAX Pro Group Limited | Administrative & support | 2021 |
| MAX Resources International Limited | Real estate | 2016 |
| MAX Wilson Coaching Ltd | Other services | 2024 |
| Maxed Labs Ltd | Information & communication | 2023 |