| Methven Terrace Management Company Limited | Households | 2005 |
| Metricab Holdings Limited | Financial services | 2025 |
| Metricab Power Engineering Limited | Construction | 1992 |
| Metricell Group Limited | Information & communication | 2007 |
| Metricell Limited | Information & communication | 2007 |
| MFD Wholesale Limited | Manufacturing | 2011 |
| MFT Industrial Limited | Real estate | 1964 |
| MG Tuition Limited | Education | 2015 |
| MH Riley Ltd | Information & communication | 2012 |
| Mhcr DEV Station Ltd | Construction | 2025 |
| Mhcr Investment Ltd | Financial services | 2025 |
| MHR Motorsport Limited | Arts & recreation | 2024 |
| MIA Makes Ltd | Wholesale & retail | 2021 |
| Miah EPC Surveyors Ltd | Professional & scientific | 2024 |
| Mibaskets Ltd | Information & communication | 2024 |
| Michael Cowan International Limited | Transport & logistics | 1980 |
| Michael Scaffolding Ltd | Construction | 2012 |
| Michael Stoop Property Services Ltd | Real estate | 2016 |
| Michael Ulloa Ltd | Other services | 2019 |
| Microconnection Limited | Information & communication | 2012 |
| Micropix Limited | Wholesale & retail | 2010 |
| Microtec UK Limited | Information & communication | 1996 |
| MID Sussex Developments Limited | Construction | 2020 |
| Midbourne Property Company Limited | Real estate | 1973 |
| Middle Earth Transport Ltd | Transport & logistics | 2023 |
| Middle East Gen-Set Association Limited | Other services | 2022 |
| Midnightclubuk Ltd | Wholesale & retail | 2021 |
| Mihrisah Limited | Real estate | 2018 |
| Mike Anthony Construction Ltd | Construction | 2015 |
| Mike Hodges Consulting Ltd | Professional & scientific | 2024 |
| Mila Lina Online Limited | Wholesale & retail | 2025 |
| Mile High Roofing & Building Ltd | Construction | 2025 |
| Milestone Visual Ltd | Professional & scientific | 2021 |
| Milioni DI Fiori Limited | Wholesale & retail | 2016 |
| Military and Aviation Advisors Ltd | Information & communication | 2023 |
| Mill END Investments Limited | Real estate | 2024 |
| Mill Gardens Management Company Ltd | Households | 2016 |
| Mill Lane Allotments Limited | Agriculture & fishing | 2020 |
| Millaa Ltd | Professional & scientific | 2016 |
| Millais Smith Bespoke Furniture Limited | Construction | 2026 |
| Millennium Interiors Limited | Construction | 2012 |
| Millennium Media Ltd | Hospitality | 2024 |
| Miller Robinson Ltd | Professional & scientific | 2013 |
| Millie and MAX Ltd | Professional & scientific | 2018 |
| Mills and Sons Limited | Professional & scientific | 1992 |
| Milne & Sons Engineering Ltd | Professional & scientific | 2025 |
| Milnwood Partners Limited | Professional & scientific | 2020 |
| Milton Mcdonald Ltd | Arts & recreation | 2010 |
| Minden Grab Hire Ltd | Construction | 2025 |
| Mindset Management Group Limited | Arts & recreation | 2023 |
| Mindstorm Makers Ltd | Education | 2025 |
| Minelock Limited | Real estate | 1989 |
| Mini Micro School Ltd | Education | 2024 |
| Minibus Travel Services Ltd. | Transport & logistics | 2002 |
| Mining and Mineral Ltd | Mining & quarrying | 2014 |
| Minshall Financial Services Limited | Financial services | 2001 |
| Minster View Leisure Ltd | Hospitality | 2021 |
| Mint Financial FP Ltd | Financial services | 2016 |
| Mint Tint Limited | Wholesale & retail | 2019 |
| Mirific Hyaena Ltd | Information & communication | 2022 |
| Mis-Sold Specialists Limited | Extraterritorial | 2013 |
| Misfits & Motors Ltd | Administrative & support | 2023 |
| Mission Command Business Ltd | Professional & scientific | 2025 |
| Mission: Strong Ltd | Arts & recreation | 2026 |
| Mitokon Ltd | Extraterritorial | 2017 |
| Mixology Limited | Hospitality | 2010 |
| Mixology School Limited | Education | 2016 |
| MJ Financial Consultants LLP | | 2017 |
| Mj&Lda Ltd | Professional & scientific | 2015 |
| MJA Heat Trace Products Limited | Manufacturing | 2010 |
| MJH Business Development Consultants Limited | Professional & scientific | 2024 |
| MJH Digital Ltd | Administrative & support | 2016 |
| MJH Ventures Limited | Professional & scientific | 2013 |
| MJP Electrical Contractors Ltd | Construction | 2020 |
| MJS Groundworks Ltd | Construction | 2021 |
| MK1 Photography Limited | Professional & scientific | 2019 |
| Mkdir Horsham Ltd | Hospitality | 2025 |
| ML Online Retail Services Ltd | Wholesale & retail | 2009 |
| ML UK Operations Limited | Information & communication | 2018 |
| Mlph Limited | Construction | 2024 |
| MM Demerger Ltd | Real estate | 2017 |
| Mmaa Limited | Information & communication | 2026 |
| MMS Supplies Limited | Construction | 2013 |
| Mndfl Coaching Ltd | Health & social care | 2023 |
| MNT Food Limited | Wholesale & retail | 2023 |
| Mobile GP Limited | Wholesale & retail | 2014 |
| Mobile TM Ltd | Construction | 2024 |
| Mobility Holdings Limited | Professional & scientific | 2026 |
| Mockbridge Ltd | Hospitality | 2017 |
| Modern Cloth Fittings Ltd | Wholesale & retail | 2025 |
| Modern Clothing Limited | Wholesale & retail | 2024 |
| Modular Interiors Group Ltd | Financial services | 2022 |
| Modular Interiors Holdings Limited | Financial services | 2014 |
| Modular Interiors Investments Ltd | Financial services | 2024 |
| Modular Interiors Limited | Construction | 2013 |
| Modular Products Limited | Wholesale & retail | 2024 |
| Modular Property Limited | Wholesale & retail | 2015 |
| Modus Interactive Limited | Information & communication | 2000 |
| Mogwaicarpentry Limited | Construction | 2014 |
| Molino Management Co. Limited | Households | 1993 |