| Maisonpascal Ltd | Real estate | 2025 |
| Majestic K9 Limited | Professional & scientific | 2021 |
| Majesticmainemajesty Ltd | Agriculture & fishing | 2025 |
| Majo Medicine Ltd | Administrative & support | 2016 |
| Make IT (Europe) Limited | Information & communication | 2011 |
| Makeprint Limited | Real estate | 1995 |
| Making Visions Happen Ltd | Other services | 2019 |
| Malcolm Robertson & Sons Limited | Professional & scientific | 2002 |
| Malcolm Smith Consultancy Limited | Professional & scientific | 2006 |
| Malcolm Wright Limited | Real estate | 1990 |
| Mallinson Fabrications Limited | Construction | 1977 |
| Mally Douglas Paving & Civils Contractors Limited | Construction | 2008 |
| Malsam Construction Ltd | Construction | 2024 |
| MAN and Van Removal Service Limited | Transport & logistics | 2019 |
| Mana KAU Farming Limited | Agriculture & fishing | 2022 |
| Manchester Driveways and Patios Limited | Construction | 2021 |
| Manner Products Ltd | Manufacturing | 2021 |
| Manoir Industries SA | | 1990 |
| Manor Construction (Cumbria) Ltd | Construction | 2025 |
| Manor House Fitness Limited | Arts & recreation | 2017 |
| Maple Utility Solutions Ltd | Construction | 2025 |
| Marc Pearce Transport Limited | Transport & logistics | 2014 |
| Marcus Jefferson Plumbing & Heating Limited | Administrative & support | 2011 |
| Mardale Road Management Limited | Households | 2004 |
| Margot Property Ltd | Real estate | 2025 |
| Marios (Silloth) Limited | Hospitality | 2021 |
| Mariposa Care Limited | Health & social care | 1994 |
| Maris Designs Ltd | Professional & scientific | 2020 |
| Marius DAN Ltd | Transport & logistics | 2025 |
| Mark Abbott Welding and Fabrication Limited | Manufacturing | 2012 |
| Mark Harper Limited | Administrative & support | 2014 |
| Mark Hunter Financial Services Ltd | Financial services | 2013 |
| Mark Lloyd Trees Ltd | Agriculture & fishing | 2025 |
| Mark O'Neill Consulting Limited | Information & communication | 2019 |
| Mark P Wannop Limited | Construction | 2003 |
| Mark Wilson (Carlisle) Ltd | Construction | 2017 |
| Marketing Dynamics (Carlisle) Limited | Professional & scientific | 2010 |
| Markland Limited | Arts & recreation | 1998 |
| Markmalloy Ltd | Transport & logistics | 2017 |
| Marlen Properties Limited | Real estate | 2024 |
| Maroi Limited | Financial services | 2016 |
| Marrs Accountancy Limited | Professional & scientific | 2020 |
| Marrs Homes Ltd | Construction | 2025 |
| Marsh Poultrywise Limited | Wholesale & retail | 2016 |
| Marsh Roofing Services Limited | Construction | 2006 |
| Marshall's and SON Limited | Administrative & support | 2019 |
| Marshall's Joinery Limited | Construction | 2026 |
| Marta Medical Ltd | Health & social care | 2015 |
| Martin Field Farms Limited | Agriculture & fishing | 1989 |
| Martin Scott Asset Management Limited | Professional & scientific | 2019 |
| Martyn Industrials Limited | Professional & scientific | 1998 |
| Martyn Reading Cars Ltd | Wholesale & retail | 2020 |
| Maryport Court Residents Association Limited | Hospitality | 1992 |
| Matchaward Limited | Construction | 1995 |
| Mathers (Cumbria) Limited | Manufacturing | 2019 |
| Matrix 1 Solution Limited | Wholesale & retail | 2004 |
| Matthew Aitchison Ltd | Arts & recreation | 2018 |
| Matthew Slessor Wealth Management Limited | Professional & scientific | 2022 |
| Matthew Spooner Ltd | Real estate | 2017 |
| Matthew's Roofing Carlisle Limited | Construction | 2022 |
| MAX Electrical (Carlisle) Ltd | Construction | 2014 |
| MAX Rentals Ltd | Real estate | 2022 |
| Maxivision Eyecare Ltd | Health & social care | 2013 |
| Maxton House Properties Limited | Real estate | 2003 |
| Maxwell Homes Limited | Construction | 2001 |
| Mayfield Residential Management Limited | Households | 2003 |
| MB Couriers (Cumbria) Ltd | Transport & logistics | 2019 |
| MB Plumbing & Heating (Cumbria) Ltd | Construction | 2020 |
| MBF Developments Ltd | Real estate | 2024 |
| MBT Roofing Ltd | Administrative & support | 2016 |
| Mburgess Ltd | Other services | 2025 |
| MBW Logistics Ltd | Transport & logistics | 2021 |
| MBW Property Management Ltd | Real estate | 2026 |
| MC IT Services Ltd | Information & communication | 2024 |
| Mcal Merchant Limited | Wholesale & retail | 2003 |
| Mcbk Logistics Ltd | Transport & logistics | 2021 |
| Mccamish Engineering Company | Professional & scientific | 2011 |
| Mccamish Plant Limited | Administrative & support | 2025 |
| Mccluskey Roofing Ltd | Construction | 2005 |
| Mccormick-Moore Ltd | Construction | 2020 |
| Mccowie Venture Holdings Limited | Financial services | 2024 |
| MCG Software Limited | Information & communication | 2007 |
| Mcgrath Estates Limited | Real estate | 2024 |
| Mcguffie Plant Hire Limited | Construction | 2013 |
| Mcintosh-Ormerod Limited | Real estate | 2025 |
| Mckellar Construction Ltd | Construction | 2005 |
| Mcknight & SON Builders Limited | Professional & scientific | 2003 |
| Mcknight Lettings Limited | Real estate | 2021 |
| MCL Haulage Ltd | Transport & logistics | 2023 |
| Mclelland & SON Limited | Wholesale & retail | 2025 |
| Mcleod House Management Company Limited | Households | 2020 |
| Mclinden Enterprises Ltd | Administrative & support | 2022 |
| MDA 1988 Limited | Professional & scientific | 2021 |
| MDH Property Limited | Real estate | 2008 |
| MDJ Electrical Services Ltd | Construction | 2025 |
| MDL Powerup Limited | Administrative & support | 2010 |
| ME Engineering Ltd | Manufacturing | 2014 |
| Meadow View House Management Limited | Real estate | 2014 |
| Meadup Ltd | Professional & scientific | 2013 |
| Mebline Ltd | Wholesale & retail | 2015 |