| M Group Water (Meica Maintenance & Projects) Limited | Professional & scientific | 1997 |
| M Group Water (Meica Specialist) Limited | Administrative & support | 1983 |
| M Group Water (Network Infrastructure) Limited | Construction | 2002 |
| M Group Water Limited | Professional & scientific | 2008 |
| M H Air Conditioning Limited | Energy | 2022 |
| M Harris Electrical Ltd | Construction | 2017 |
| M Innovations Ltd | Administrative & support | 2009 |
| M J Flooring & Carpets Limited | Construction | 2006 |
| M J M Control Ltd | Construction | 2019 |
| M J P Property Services Limited | Real estate | 2015 |
| M K Properties Northampton Limited | Real estate | 2015 |
| M K Securities Limited | Professional & scientific | 2007 |
| M K Windows Limited | Wholesale & retail | 2003 |
| M L Canavan Property Consultancy Ltd | Professional & scientific | 2022 |
| M Lawless Property Holdings Limited | Real estate | 2024 |
| M P Gwilliam Kitchen & Build Specialist Limited | Construction | 2025 |
| M Skinner Rigging Ltd | Other services | 2011 |
| M Tech 66 Limited | Information & communication | 2013 |
| M Thakrar Limited | Health & social care | 2025 |
| M&C Online Shop Limited | Wholesale & retail | 2026 |
| M&D Accounting Services Ltd | Professional & scientific | 2024 |
| M&G-Ro Limited | Wholesale & retail | 2022 |
| M&J Endymion Ltd | Professional & scientific | 2023 |
| M&L Fire Safety Ltd | Construction | 2020 |
| M&M Bespoke Services Ltd | Construction | 2025 |
| M&S Homesphere Ltd | Real estate | 2022 |
| M&S Performance Ltd | Wholesale & retail | 2024 |
| M&T Events Ltd | Hospitality | 2024 |
| M. Bridge Carpentry Ltd | Manufacturing | 2025 |
| M. Webb Property Holdings Ltd | Real estate | 2025 |
| M.B.S.M Ltd | Other services | 2026 |
| M.D. Beckwith Limited | Transport & logistics | 1965 |
| M.R. CAD Tech Limited | Administrative & support | 2013 |
| M10 Edge, Ltd. | Manufacturing | 2019 |
| M13HDN Consultancy Ltd | Information & communication | 2026 |
| M25 Vans Limited | Wholesale & retail | 2018 |
| MA Bookkeeping and Payroll Services Ltd | Professional & scientific | 2024 |
| MA Direct Accounting Limited | Professional & scientific | 2022 |
| MA Harlow Ltd | Hospitality | 2024 |
| MA Hertford Ltd | Hospitality | 2020 |
| MA Primary Ltd | Health & social care | 2020 |
| Maaa Services Limited | Real estate | 2020 |
| Mabel’S Property Services Ltd | Real estate | 2023 |
| MAC & Burg Holdings Limited | Real estate | 2014 |
| MAC & Burg Limited | Financial services | 2022 |
| Mack Nationwide Limited | Other services | 2022 |
| Macnair Medical Limited | Health & social care | 2024 |
| Macro Golf Studios Ltd | Arts & recreation | 2023 |
| Macrohard Systems Ltd | Information & communication | 2022 |
| Mactavish Group Limited | Extraterritorial | 2006 |
| Mactavish Hepburn Limited | Extraterritorial | 2002 |
| Mactavish Limited | Information & communication | 1998 |
| Mactavish UA Limited | Financial services | 2016 |
| MAD Lamb Media Ltd | Information & communication | 2019 |
| Madame MOP & Baroness Bucket Ltd | Administrative & support | 2025 |
| Maddox Forestry & ARB Ltd | Agriculture & fishing | 2020 |
| Made by Gravity Ltd | Administrative & support | 2007 |
| Made for Events Limited | Information & communication | 2025 |
| Made With Clay Studio C.I.C. | Arts & recreation | 2019 |
| Madewell Roofing Limited | Construction | 2024 |
| Madri Properties Limited | Real estate | 2022 |
| Madsan Electrical Ltd | Construction | 2020 |
| Maggie and Chambers Ltd | Professional & scientific | 2024 |
| Mahers Trophies Limited | Wholesale & retail | 2014 |
| MAID2CLEANSE Ltd | Administrative & support | 2021 |
| Maiden Care Services Limited | Health & social care | 2014 |
| Main Door Security Limited | Financial services | 2019 |
| Mainline Electrical Site Services Ltd | Construction | 2018 |
| Maintain 4 Life Limited | Construction | 2024 |
| Maintenance Property Service Ltd | Construction | 2021 |
| Maisha Housing Ltd | Other services | 2017 |
| Maison Riche Ltd | Information & communication | 2022 |
| Majenat Ltd | Health & social care | 2010 |
| Majestic Plumbing and Heating Limited | Construction | 2017 |
| Majesty Grading Company Ltd | Other services | 2025 |
| Majoris Supply Ltd | Wholesale & retail | 2024 |
| Make a Scene Construction Limited | Wholesale & retail | 2024 |
| Make a Shake (Stevenage) Limited | Hospitality | 2014 |
| Make Your Day Event Hire Limited | Other services | 2019 |
| Makeup by Hayley Ltd | Other services | 2024 |
| Makeup by Rosie Ltd | Other services | 2026 |
| Makeup Wedding Parties Ltd | Arts & recreation | 2010 |
| Makhenzi Catering Ltd | Hospitality | 2025 |
| Makin Marquees Holdings Limited | Financial services | 2025 |
| Makin Marquees Limited | Arts & recreation | 2022 |
| Makk Services Ltd | Transport & logistics | 2025 |
| Malisafi Limited | Wholesale & retail | 2024 |
| Malishev Engineers Limited | Professional & scientific | 2014 |
| Maliyackal Homes Ltd | Real estate | 2018 |
| Mallard Rise (Knebworth) Management Company Limited | Real estate | 1986 |
| Maloney & Sons Ltd | Construction | 2023 |
| Malva Botanics Ltd | Manufacturing | 2020 |
| Malvern House Management Company Limited | Households | 2005 |
| MAN Bioscience Ltd | Professional & scientific | 2011 |
| MAN Projects Limited | Construction | 2007 |
| Management & Consultancy (UK) Limited | Real estate | 2003 |
| Manasas Gift Ltd | Professional & scientific | 2025 |
| Mandarin House 888 Limited | Hospitality | 2023 |
| Maneli Ltd | Construction | 2009 |
| Mangone Limited | Extraterritorial | 2013 |