| Marsh Garage Service Centre Limited | Wholesale & retail | 2003 |
| Marsh Project Solutions Ltd | Professional & scientific | 2023 |
| Martin Phelps Photography Limited | Professional & scientific | 2013 |
| Matlex Systems Limited | Construction | 2023 |
| Matrix Composite Materials Company Limited | Wholesale & retail | 1997 |
| Matthew Fuller Residential Limited | Real estate | 2020 |
| Mayfield Home Trust Limited | Health & social care | 1987 |
| Maylie Innovations Limited | Construction | 2025 |
| Mcbride Property Holdings Ltd | Real estate | 2024 |
| Mccounting Ltd | Professional & scientific | 2011 |
| Mcgoldrick GUO Limited | Real estate | 2021 |
| Mcqueen Media Ltd | Construction | 2010 |
| Mdhp Consulting Engineers Ltd | Professional & scientific | 2018 |
| MDL Kelex Group Limited | Manufacturing | 2019 |
| Mearas Ltd | Information & communication | 2024 |
| Meet&Greet@Heathrow Airport Ltd | Real estate | 2024 |
| MEF Holdings Limited | Financial services | 2017 |
| Meko 2016 Limited | Construction | 2016 |
| Meko Compliance Services Limited | Extraterritorial | 2021 |
| Meko Property Limited | Real estate | 2026 |
| Meldb Properties Ltd | Construction | 2022 |
| Mentoring @ Bridge Limited | Education | 2026 |
| Merrell People Ltd | Professional & scientific | 2019 |
| Merretts Heating Services Limited | Administrative & support | 2016 |
| Merryfield Construction Limited | Construction | 2003 |
| Mesh Industries Limited | Professional & scientific | 1990 |
| Metek Holdings Limited | Financial services | 2015 |
| Metek Investment Solutions Limited | Extraterritorial | 2007 |
| Metek Modular Building Ltd | Manufacturing | 2006 |
| Metek PLC | Manufacturing | 2000 |
| Metickulous Ltd | Agriculture & fishing | 2021 |
| MI Services Bristol Limited | Construction | 2013 |
| Michael Jules Ltd | Households | 2017 |
| Michael Naylor Surveyors Ltd | Professional & scientific | 2013 |
| Mike Davis Limited | Administrative & support | 2018 |
| Mike Paul Electrical Service Limited | Construction | 2002 |
| Mikris Finishers Limited | Construction | 2011 |
| Mill ROW Cottages Management Limited | Real estate | 2004 |
| Millerwyck Homes Ltd | Real estate | 2026 |
| Millwood Motor Company Limited | Wholesale & retail | 1965 |
| Milner Browne Limited | Information & communication | 2011 |
| Minchinbury Limited | Financial services | 2017 |
| Miramar Cars Limited | Wholesale & retail | 2019 |
| MJ Woodwork Limited | Manufacturing | 2019 |
| MJD Projects Limited | Professional & scientific | 2013 |
| Mode Hair and Beauty Ltd | Other services | 2018 |
| Moes Arborists Limited | Administrative & support | 2023 |
| Moes Group Limited | Agriculture & fishing | 2018 |
| Moes Landscaping Limited | Construction | 2021 |
| Moes Mowing Limited | Agriculture & fishing | 2024 |
| Mojo Ltd | Wholesale & retail | 2004 |
| Montpellier 2023 Limited | Professional & scientific | 2023 |
| Moonflower in Stroud Ltd | Wholesale & retail | 2017 |
| Moonflower of Stroud Limited | Wholesale & retail | 2002 |
| More Than Protein Limited | Wholesale & retail | 2015 |
| Morgan Brown Hair Body Beauty Limited | Other services | 2024 |
| Moss Motors (Stroud) Ltd | Wholesale & retail | 2019 |
| Moss Road & Race Ltd | Wholesale & retail | 2021 |
| Motocat Ltd | Wholesale & retail | 2015 |
| Mountain Road Software Ltd | Information & communication | 2019 |
| MR Slurp Ltd | Wholesale & retail | 2022 |
| MRC IT Services Ltd | Information & communication | 2011 |
| MS Commercial Finance Ltd | Financial services | 2016 |
| MSC Joinery Ltd | Administrative & support | 2017 |
| MTS Penderi Solar 2 Limited | Energy | 2014 |
| MTS Tonge Solar Limited | Construction | 2013 |
| My Equity Release Choices Limited | Extraterritorial | 2020 |
| My Financial Choices Limited | Financial services | 2020 |
| My Investment Choices Limited | Extraterritorial | 2020 |
| My Mortgage Choices Limited | Extraterritorial | 2020 |
| My Shared Ownership Choices Limited | Extraterritorial | 2020 |
| N K Newman Limited | Construction | 2003 |
| NAE TOO Shabby Ltd | Wholesale & retail | 2015 |
| National Oilwell (U.K.) Limited | Extraterritorial | 1910 |
| National Oilwell Varco UK Limited | Mining & quarrying | 1966 |
| NC Investments Limited | Real estate | 1998 |
| Need a Joiner Limited | Construction | 2008 |
| Nelic Ltd | Manufacturing | 2023 |
| Nemesis Investments Limited | Professional & scientific | 1996 |
| Netalg Innovations Limited | Information & communication | 2011 |
| New Build Snagging Ltd | Construction | 2021 |
| Newton Consulting Sprl. Limited | Manufacturing | 2011 |
| Nicholas Brown Consultants Limited | Professional & scientific | 2000 |
| Nick Griffith Estate Agents Limited | Real estate | 2014 |
| Nidus Training Ltd | Arts & recreation | 2019 |
| Nimble Elearning Ltd | Information & communication | 2009 |
| Nippy Chippy Ltd | Hospitality | 2020 |
| NIX Bar Limited | Hospitality | 2020 |
| NJP Management Ltd | Administrative & support | 2018 |
| Noble & Fletcher Limited | Construction | 2018 |
| North Ryeford Garage Limited | Wholesale & retail | 2005 |
| North Side Aviation Ltd | Manufacturing | 2025 |
| North Weald Solar Limited | Energy | 2021 |
| Nortim Precision Engineering Limited | Manufacturing | 1971 |
| Nortim Tools Limited | Extraterritorial | 2021 |
| NOT SO Magic Apps Limited | Information & communication | 2022 |
| NOV Downhole Eurasia Limited | Mining & quarrying | 2002 |
| NOV Process & Flow Technologies UK Limited | Manufacturing | 1935 |
| NOV UK Korea LP | | 2010 |
| NR Art Ltd | Arts & recreation | 2025 |