| Magic Maids Cleaning Ltd | Administrative & support | 2023 |
| Magill Property Developments Limited | Construction | 2016 |
| Magnetronix Ltd | Information & communication | 2026 |
| Magpie and the MOB Ltd | Wholesale & retail | 2021 |
| Magpie Metal Fabrications Limited | Manufacturing | 2004 |
| Maho Sports Ltd | Wholesale & retail | 2025 |
| Major Construction Group Ltd | Construction | 2026 |
| Makame Properties Ltd | Real estate | 2024 |
| Makjon Consult Limited | Construction | 2015 |
| Malazoo Limited | Information & communication | 2007 |
| Malone Roofing Limited | Construction | 2009 |
| Malp Projects Limited | Information & communication | 2019 |
| Malp Service Limited | Professional & scientific | 2010 |
| Maltwillow Limited | Other services | 1984 |
| Mancave Barbers (Newbury) Ltd | Other services | 2023 |
| Mangrove Integrated Ltd | Administrative & support | 2025 |
| Manicom Global Logistics Ltd | Transport & logistics | 2025 |
| Mankoo Consultants Limited | Professional & scientific | 2016 |
| Manor Farm Tidmarsh Ltd | Construction | 2016 |
| Mansion House Newbury Ltd | Real estate | 2023 |
| Manton Cottages Limited | Real estate | 2019 |
| Mantri Advisory Limited | Other services | 2025 |
| Manufacturing Investments Limited | Financial services | 1991 |
| Manycourt Properties Limited | Real estate | 2017 |
| Mapa Tech Ltd | Information & communication | 2022 |
| Maple Gardens (Milton) Limited | Households | 2016 |
| Maplespeen Freehold Limited | Households | 2021 |
| Maplespeen Management Company Limited | Households | 2004 |
| Maplestone Construction Limited | Construction | 2014 |
| Marbin Limited | Administrative & support | 1997 |
| Marbus Developments Limited | Construction | 2007 |
| Marc Allen Limited | Real estate | 2001 |
| Marcham Scientific Limited | Professional & scientific | 1996 |
| Marchetti Holdings Limited | Agriculture & fishing | 1986 |
| Marcin S Nowak Limited | Transport & logistics | 2017 |
| Marden's Club Ltd | Arts & recreation | 2018 |
| Mariana Properties Ltd | Real estate | 2021 |
| Mariass Limited | Administrative & support | 2013 |
| Maricol Developments Limited | Construction | 2020 |
| Marivy Limited | Professional & scientific | 1992 |
| Mark Clayton Consultancy Ltd | Professional & scientific | 2023 |
| Mark Dunnett Limited | Professional & scientific | 2019 |
| Mark Flitton Limited | Manufacturing | 2018 |
| Mark Sheircliff Consulting Ltd | Construction | 2022 |
| Markal Consulting Limited | Information & communication | 2007 |
| Marketgreen Limited | Construction | 2013 |
| Marketing North Limited | Manufacturing | 1998 |
| Marketingunity Limited | Information & communication | 1996 |
| Marlborough Court Residents' Association (Hungerford) Limited | Households | 1985 |
| Marldon Christmas Tree Company Limited | Wholesale & retail | 2013 |
| Marldon Lodges Ltd | Hospitality | 2019 |
| Marola Dental Laboratories Ltd | Manufacturing | 2021 |
| Marque Media Enterprises Ltd | Administrative & support | 2025 |
| Marque Media Group Ltd | Information & communication | 2025 |
| Marshall Mechanical Technical Services Ltd | Professional & scientific | 2014 |
| Marske Financial Ltd | Professional & scientific | 2005 |
| Martin Allen Consulting Limited | Information & communication | 2010 |
| Martlet and Crown Developments Ltd | Construction | 2024 |
| Maruti Netsec Consultancy Limited | Information & communication | 2026 |
| Marwood Electrical Company Limited | Wholesale & retail | 1977 |
| Mary Gober International Limited | Education | 2003 |
| Mary Hare | Education | 1995 |
| Mary Hare Services Ltd | Manufacturing | 1996 |
| Mary Hare Total Hearing Solutions Limited | Wholesale & retail | 2006 |
| Mary Odil Limited | Health & social care | 2022 |
| Mass Group Limited | Professional & scientific | 1999 |
| Master Sped Ltd | Wholesale & retail | 2024 |
| Matatan Ltd | Hospitality | 2024 |
| Matchem Limited | Other services | 2021 |
| Mateo Advisory Services Limited | Professional & scientific | 2026 |
| Materials Expertise Limited | Professional & scientific | 2021 |
| Mathilda Limited | Wholesale & retail | 2009 |
| Mati Holdings Limited | Professional & scientific | 2020 |
| Matmap Survey Ltd | Professional & scientific | 2020 |
| Matt Stephens Plumbing and Heating Ltd | Construction | 2022 |
| Matthew Fedrick Ltd | Professional & scientific | 2014 |
| Maughans Limited | Professional & scientific | 2006 |
| Maundopoly Ventures Ltd | Financial services | 2023 |
| Maven B2B Limited | Professional & scientific | 2025 |
| Maves Beauty Ltd | Wholesale & retail | 2021 |
| Mavid Investments Limited | Financial services | 2022 |
| Maximilian Films Ltd | Information & communication | 2023 |
| Mayflower Grove (Bramley) Management Company Ltd | Households | 2025 |
| Mazanka Wellness Retreat Ltd | Extraterritorial | 2025 |
| Mbawa Limited | Administrative & support | 2018 |
| MBL Sponsorship and Events Limited | Arts & recreation | 2012 |
| Mblaw (Newbury) Ltd | Professional & scientific | 2010 |
| MC Media Consulting Ltd | Professional & scientific | 2023 |
| MC Operations Limited | Transport & logistics | 2021 |
| MC2 Tiles and Flooring Limited | Wholesale & retail | 2007 |
| Mccarthy MOT Centre Limited | Wholesale & retail | 2002 |
| Mcdd Limited | Professional & scientific | 2025 |
| Mcdoodies Ltd | Households | 2025 |
| Mckenzie Csapo Investments Limited | Real estate | 2024 |
| Mckenzie Investments Limited | Real estate | 2020 |
| Mcsisters Limited | Real estate | 2024 |
| MCT Nutrition Limited | Administrative & support | 2009 |
| MD Auto Solutions Limited | Wholesale & retail | 2020 |
| Md-R Investments Ltd | Financial services | 2021 |
| MDB Arts Ltd | Wholesale & retail | 2019 |