| Maltby Property & Maintenance Company Limited | Construction | 1994 |
| Malthouse of Basildon Limited | Hospitality | 1958 |
| Maltings Management Services Limited | Professional & scientific | 2006 |
| Mama Mackintosh Foods Ltd | Hospitality | 2024 |
| MAN With a Jumbo Van Ltd | Transport & logistics | 2016 |
| Management (LB) Limited | Other services | 2022 |
| Management Forty-Four Limited | Other services | 2024 |
| Managing Angra Financial UK Ltd | Professional & scientific | 2012 |
| Manam Homes Limited | Real estate | 2025 |
| Mandal Plastic Surgery Ltd | Health & social care | 2023 |
| Mandescu Transport Ltd | Transport & logistics | 2025 |
| Manea D Ltd | Transport & logistics | 2015 |
| Manifold Enterprises Ltd | Real estate | 2025 |
| Manjo's Limited | Health & social care | 2014 |
| Manna Technology Solutions Ltd | Information & communication | 2015 |
| Manning Hotels Limited | Extraterritorial | 2012 |
| Manningtree Vintage Vibes Ltd | Wholesale & retail | 2024 |
| Mannson Freight Services Ltd. | Transport & logistics | 1991 |
| Manor Homes London Limited | Construction | 2021 |
| Manor Industrial Supplies Limited | Wholesale & retail | 2001 |
| Manosoft Ltd | Information & communication | 2012 |
| Mansell Taylor Restoration Ltd | Manufacturing | 2014 |
| Mansol Ltd | Professional & scientific | 2023 |
| Mansworth Construction Limited | Construction | 2017 |
| Mantra Assets Limited | Real estate | 2008 |
| Manushree Limited | Health & social care | 2012 |
| Manutan Traders Group Limited | Professional & scientific | 2005 |
| Maots Limited | Wholesale & retail | 2022 |
| MAP Drainage Solutions Ltd | Water & waste | 2026 |
| Mapa Construction Ltd | Construction | 2018 |
| Maple & Finch Boutique Ltd | Wholesale & retail | 2024 |
| Maple Tree Property Solutions Ltd | Real estate | 2024 |
| Maplin Building Services Limited | Real estate | 2026 |
| Maplin Services Limited | Water & waste | 2019 |
| Marals Solutions Ltd | Transport & logistics | 2019 |
| Maraltrans Limited | Transport & logistics | 2012 |
| Maranatha African Food Supply Limited | Hospitality | 2015 |
| Marc Massey Construction Ltd | Construction | 2015 |
| Marcco FIX Ltd | Construction | 2020 |
| Marcel Consulting Services Limited | Information & communication | 2023 |
| Marcia 4TH Limited | Health & social care | 2012 |
| Marco's Bar Limited | Hospitality | 2003 |
| Marcon Group Limited | Financial services | 2026 |
| Marcos Real Estate Limited | Administrative & support | 2019 |
| Marcus Baum Solicitors Ltd | Professional & scientific | 2006 |
| Marden Homes Holdings Limited | Financial services | 2017 |
| Marden Maldon Limited | Construction | 2023 |
| Marden New Homes Limited | Construction | 2019 |
| Marden Signs & Designs Limited | Administrative & support | 1995 |
| Mardens (Trading) Limited | Administrative & support | 2010 |
| Mareva Property Ltd | Hospitality | 2025 |
| Marhume Limited | Wholesale & retail | 2025 |
| Maria Lescov Ltd | Information & communication | 2021 |
| Marian 23 Trans Ltd | Transport & logistics | 2023 |
| Marianis Services Ltd | Hospitality | 2024 |
| Marianne & VM Ltd | Administrative & support | 2019 |
| Maricel Haulage Ltd | Transport & logistics | 2024 |
| Marin Spirdonov Trading Limited | Transport & logistics | 2025 |
| Marion Jtjj Ltd | Health & social care | 2022 |
| Maritime Cyber Solutions Limited | Administrative & support | 2016 |
| Mariusprokompani Ltd | Transport & logistics | 2020 |
| Mark & Sparks Ltd | Construction | 2016 |
| Mark Hatter Associates Limited | Health & social care | 2011 |
| Mark J Morsley and Associates Ltd | Financial services | 2010 |
| Mark Lighting Limited | Wholesale & retail | 2015 |
| Mark NIC Management Services Limited | Real estate | 2011 |
| Mark Wass Services Limited | Construction | 2015 |
| Mark Waters Limited | Other services | 2016 |
| Market Street (Oldham) Ltd | Real estate | 2024 |
| Marketing Elect Limited | Professional & scientific | 2020 |
| Markham Automatic Gates Limited | Manufacturing | 1992 |
| Markham Group Ltd | Construction | 2024 |
| Markov Global Ltd | Other services | 2026 |
| Marksons Properties Company Ltd | Real estate | 2025 |
| Marky 1 Driving Tuition Limited | Education | 2023 |
| Marlborough Heights (Billericay) Management Company Limited | Administrative & support | 1983 |
| Marlborough Pharmaceuticals Limited | Manufacturing | 2005 |
| Marlene Trading Limited | Wholesale & retail | 2024 |
| Marlow Capital Limited | Administrative & support | 2012 |
| Marlow Integrated Designs Limited | Manufacturing | 1980 |
| Marlyn Consultancy Ltd | Professional & scientific | 2024 |
| Marlyn Recruitment Ltd | Administrative & support | 2018 |
| Marni London Ltd | Administrative & support | 2025 |
| Maro Survey Ltd | Professional & scientific | 2023 |
| Marostudios Limited | Information & communication | 2015 |
| Marques Duarte Limited | Health & social care | 2022 |
| Marsab Limited | Real estate | 2021 |
| Marshall Securities Ltd | Administrative & support | 2025 |
| Marshalls Consultancy Services Ltd | Professional & scientific | 2025 |
| Martaosam Home Limited | Health & social care | 2022 |
| Martin and SON Electrical Ltd | Construction | 2025 |
| Martina a Ltd | Professional & scientific | 2019 |
| Martynak Ltd | Transport & logistics | 2023 |
| Maru Karate KAI CIC | Arts & recreation | 2024 |
| Marvel-Mac Ventures Ltd | Wholesale & retail | 2020 |
| Marvellous Creations Ltd | Wholesale & retail | 2009 |
| Marvplace Ltd | Wholesale & retail | 2025 |
| Marydaro Limited | Health & social care | 2015 |
| Maryo Drive Ltd | Transport & logistics | 2017 |
| Maryokon Ltd | Construction | 2017 |