| M3 Essentials Ltd | Wholesale & retail | 2026 |
| M3U Ltd | Information & communication | 2003 |
| M44 Ltd | Information & communication | 2024 |
| M8 Childcare Limited | Health & social care | 2025 |
| M8 Residencies Limited | Real estate | 2025 |
| MAB Accountancy Hub Ltd | Professional & scientific | 2021 |
| Mabbott Consultancy Limited | Professional & scientific | 2015 |
| Mabelvale Homes Ltd | Real estate | 2026 |
| Mablethorpe NG Limited | Energy | 2023 |
| Macarthur Residential Investments Ltd | Real estate | 2024 |
| Macaulay Edwards Independent Financial Consultants Limited | Financial services | 2007 |
| Maceywest Bar Co Limited | Hospitality | 2026 |
| Macfit Limited | Construction | 2007 |
| Machynys Ltd | Professional & scientific | 2019 |
| Mack Estates Limited | Extraterritorial | 2025 |
| Mack Group Europe Ltd | Financial services | 2024 |
| Mack Group International Ltd | Extraterritorial | 2024 |
| Mack Group Ireland Ltd | Extraterritorial | 2024 |
| Mack Homes Limited | Extraterritorial | 2025 |
| Mack Opco Ltd | Administrative & support | 2005 |
| Mack Personnel Limited | Administrative & support | 2014 |
| Mack Power Ltd | Construction | 2023 |
| Mack Propco Limited | Real estate | 2003 |
| Mack Property Group Limited | Real estate | 2025 |
| Mack Residential Limited | Real estate | 2005 |
| Mackay & Associates Limited | Professional & scientific | 2004 |
| Mackintosh Aviation Limited | Transport & logistics | 2008 |
| Maclean Connect Limited | Financial services | 2021 |
| Macoe Solutions Limited | Information & communication | 2015 |
| Macontrols (Holdings) Limited | Financial services | 2016 |
| Macontrols Limited | Manufacturing | 2003 |
| Macrae Aviation Limited | Transport & logistics | 2013 |
| Macrae Capital Limited | Real estate | 2013 |
| Macs Maintenance & Cleaning Services Limited | Administrative & support | 2007 |
| Macsen Group Ltd | Construction | 2025 |
| Macsoft Limited | Information & communication | 1983 |
| Mactec Solutions Ltd | Professional & scientific | 2025 |
| Macxout Ltd | Other services | 2025 |
| MAD Living Limited | Professional & scientific | 2022 |
| Maddison House | Other services | 2021 |
| Maddocks Properties Limited | Real estate | 2018 |
| Made by Hive Ltd | Information & communication | 2014 |
| Made Media Holdings Limited | Financial services | 2022 |
| Made Media Ltd | Information & communication | 2002 |
| Madeley Practice Limited | Health & social care | 2014 |
| Madgeorgia Limited | Administrative & support | 2010 |
| Madisons Cheltenham Ltd | Hospitality | 2022 |
| Madle IT Services Limited | Information & communication | 2007 |
| Madra Veterinary Clinic Limited | Professional & scientific | 2023 |
| Madventure Limited | Administrative & support | 2009 |
| Maelstrom Nexial Ltd | Professional & scientific | 2023 |
| Maes Construction Limited | Extraterritorial | 2000 |
| Maestro Data Limited | Information & communication | 2023 |
| Magcap Ventures Limited | Construction | 2020 |
| Magic Moments Childcare Ltd | Administrative & support | 2005 |
| Magical Touch Limited | Health & social care | 2019 |
| Magna Assets Ltd | Construction | 2017 |
| Magna B2B Ltd. | Professional & scientific | 2016 |
| Magna Industrials Limited | Manufacturing | 1983 |
| Magnum Circus Ltd | Other services | 2014 |
| Magnus Brands Limited | Wholesale & retail | 2022 |
| Magnus James Property Recruitment Ltd | Administrative & support | 2022 |
| Magri Williams Ltd | Professional & scientific | 2019 |
| Magsi Ventures Limited | Wholesale & retail | 2026 |
| Magwoods Consulting Ltd | Wholesale & retail | 2025 |
| Mahonia Advisory Limited | Professional & scientific | 2025 |
| Maid in Bury Ltd. | Households | 2016 |
| Maida Management Limited | Real estate | 1999 |
| Maida Vale Apartments ( Cheltenham) Limited | Households | 2023 |
| Maids Cleaning Group Limited | Administrative & support | 2018 |
| Main Tax Co Limited | Professional & scientific | 2024 |
| Maina Trans Ltd | Transport & logistics | 2019 |
| Mainpoint Fire Protection Limited | Wholesale & retail | 1991 |
| Mainport Putter & Partners LLP | | 2015 |
| Mainstay Housing & Support Ltd | Hospitality | 2016 |
| Maison Chéri Ltd | Manufacturing | 2025 |
| Maitai Events Cotswolds Limited | Professional & scientific | 2023 |
| MAJ Media Ltd | Information & communication | 2024 |
| Majestic Studios Limited | Arts & recreation | 2026 |
| Major Distribution Supplies Ltd | Wholesale & retail | 2023 |
| MAK Property Investment Ltd | Real estate | 2022 |
| MAK Rail System Engineering Services Limited | Professional & scientific | 2022 |
| MAK Relocations Ltd | Administrative & support | 2017 |
| Makada Consulting Limited | Professional & scientific | 2007 |
| Makal Jewellery Limited | Wholesale & retail | 2018 |
| Makin Projects Ltd | Arts & recreation | 2012 |
| Making a Difference Adventures CIC | Other services | 2022 |
| Making Life Simple Limited | Health & social care | 2017 |
| Makk Ltd | Professional & scientific | 2020 |
| Makonye Services Limited | Public administration | 2019 |
| Makteam Ltd | Construction | 2023 |
| Malaro Games Ltd | Manufacturing | 2024 |
| Maldon Fields Ltd | Other services | 2021 |
| Malesa Ltd | Transport & logistics | 2015 |
| Malferna View (Astwood Green) Management Company Limited | Households | 2015 |
| Malinka Cheltenham Ltd | Wholesale & retail | 2026 |
| Mallard and Enright Holdings Limited | Financial services | 2025 |
| Mallow Inc Ltd | Wholesale & retail | 2025 |
| Malmesbury Woodworking Company Limited | Manufacturing | 1970 |
| Malthouse Investments Limited | Real estate | 1980 |