| Lsdesignuk Ltd | Manufacturing | 2020 |
| Lsgb Projects Limited | Professional & scientific | 2017 |
| Lukelewis.Closing Ltd | Professional & scientific | 2026 |
| Luxe Tiling & Bathrooms Ltd | Construction | 2023 |
| Luxury Invest Group Ltd | Professional & scientific | 2020 |
| Lynch Electrical Ltd | Manufacturing | 2015 |
| Lynchpin Support Ltd | Professional & scientific | 2022 |
| Lyzzick Hall Hotel Limited | Hospitality | 2021 |
| M & J Bitter END Ltd | Hospitality | 2020 |
| M + D Properties (Cumbria) Ltd | Real estate | 1994 |
| M a Properties Cumbria Ltd | Real estate | 2026 |
| M B Engineering Cumbria Limited | Professional & scientific | 2017 |
| M Huddart & Co Limited | Professional & scientific | 2002 |
| M J Straughton Painters & Decorators Ltd | Construction | 2020 |
| M Taylor Associates Limited | Professional & scientific | 2011 |
| M&G EPC Limited | Professional & scientific | 2013 |
| M-Sport Limited | Arts & recreation | 1987 |
| M-Sport UK Limited | Arts & recreation | 2022 |
| M.A.E. Planning Ltd | Administrative & support | 2014 |
| M.B.C.Investments Limited | Real estate | 1927 |
| MAC Musica Limited | Education | 2002 |
| Maggie Phillips Maryport Limited | Other services | 2020 |
| Maintenance Consult Planning Ltd | Administrative & support | 2023 |
| Majorleigh Limited | Information & communication | 1994 |
| Malcolm Wilson (Motor Sport) Limited | Arts & recreation | 1979 |
| Manage Your Block Property Limited | Households | 2024 |
| Mane Street Barbers Ltd | Other services | 2013 |
| Manesty Makes Limited | Wholesale & retail | 2024 |
| Manor House Hotel Cockermouth Limited | Hospitality | 2002 |
| Manor Properties (Cumbria) Limited | Hospitality | 2014 |
| Mansion House (Greysouthen) Management Company Limited | Households | 2026 |
| Mariella's Kitchen Limited | Manufacturing | 2024 |
| Mark Hitchen Construction Limited | Construction | 2007 |
| Marklaine Haulage Limited | Transport & logistics | 2013 |
| Marlborough Joinery Cumbria Limited | Construction | 2019 |
| Marr Property Partners Ltd | Real estate | 2025 |
| Martin Goode Mrics Limited | Professional & scientific | 2010 |
| Maryport Fishing Company Limited | Hospitality | 2011 |
| Matthew Jackson Builders Limited | Construction | 2016 |
| Mayo Kindergarten Limited | Education | 2006 |
| MB Counselling & Psychotherapy Limited | Health & social care | 2021 |
| Mcavoy Engineering Ltd | Professional & scientific | 2024 |
| Mcgrath (Cockermouth) Limited | Wholesale & retail | 2002 |
| Mcguire Properties Ltd | Real estate | 2019 |
| MD Engineering Cumbria Limited | Administrative & support | 2019 |
| Meadow View Enterprises Ltd | Professional & scientific | 2016 |
| Medd and Ostle Ltd | Hospitality | 2025 |
| MEDIA8 Limited | Other services | 2010 |
| Mehak Zahra Smiles Ltd | Health & social care | 2025 |
| Melbreak House Limited | Hospitality | 2026 |
| Melbreck Associates Ltd | Professional & scientific | 2022 |
| Mellbeck Ltd. | Wholesale & retail | 1994 |
| Mellbrek Ltd | Information & communication | 2025 |
| Memw Management Limited | Financial services | 2008 |
| Mercury Stone Advance Ltd | Professional & scientific | 2022 |
| Mercury Stone Holdings Ltd | Financial services | 2019 |
| Mercury Stone Limited | Professional & scientific | 2010 |
| Messrs Bland Limited | Agriculture & fishing | 2023 |
| Messrs Weightman Ltd | Agriculture & fishing | 2025 |
| MF Lame Limited | Hospitality | 2023 |
| Mgmrics Ltd | Professional & scientific | 2019 |
| MH Property & Construction Limited | Professional & scientific | 2021 |
| Michael Heron & SON Builders Ltd | Construction | 2011 |
| Michael Rusman Limited | Health & social care | 2012 |
| Middle Farm Estate Limited | Extraterritorial | 2014 |
| Midtown Cottages (High Lorton) Management Company Limited | Households | 1997 |
| Mike Ames Technical Ltd | Professional & scientific | 2022 |
| Millcroft Holdings (Cumbria) Limited | Financial services | 2024 |
| Millcroft Veterinary Group Limited | Professional & scientific | 2020 |
| Mind Over Matter Holistics Limited | Health & social care | 2025 |
| Minx Engineering Ltd | Professional & scientific | 2003 |
| Mission Excel Ltd | Professional & scientific | 2024 |
| Missioncx Limited | Professional & scientific | 2006 |
| Mitchell's Auction Company Limited | Professional & scientific | 1873 |
| Mitre Court (Cockermouth) Limited | Households | 2006 |
| MJS (Cumbria) Limited | Administrative & support | 2021 |
| MLG Developers Limited | Construction | 2014 |
| MLT Holdings Limited | Financial services | 2015 |
| MN Groundwork & Construction Limited | Construction | 2024 |
| Mobile Cattle Services Ltd | Administrative & support | 2003 |
| Mockerkin Management Limited | Transport & logistics | 2015 |
| Montgomery Brown Holdings Ltd | Real estate | 2015 |
| Moore Commercial Law Limited | Professional & scientific | 2016 |
| Moreton Solutions Limited | Professional & scientific | 2011 |
| Morlec Cumbria Limited | Construction | 2018 |
| Morris Technical Consultancy Ltd | Professional & scientific | 2020 |
| Morrison Building Services (Cumbria) Ltd | Construction | 2012 |
| Moukarram Healthcare Ltd | Other services | 2014 |
| Mountain Sense Limited | Other services | 2011 |
| Mountain View Bespoke Skin & Aesthetics Ltd | Other services | 2026 |
| MS Emergency Management Ltd | Professional & scientific | 2019 |
| Msrt Limited | Manufacturing | 2017 |
| MT Fleet Ltd | Households | 2017 |
| MTS Nuclear Services Ltd | Other services | 2023 |
| MU MU Media Ltd | Administrative & support | 2000 |
| Murray Property Developments Limited | Construction | 2003 |
| Musco Ltd | Professional & scientific | 2018 |
| Museum Identity Limited | Arts & recreation | 2008 |
| Mwkb Consultancy Services Limited | Administrative & support | 2023 |
| N Robson Consulting Limited | Professional & scientific | 2017 |