| Make Design Create Limited | Information & communication | 2013 |
| Make ME Social Limited | Administrative & support | 2024 |
| Makemelocal.Com Ltd. | Information & communication | 2013 |
| Makers ROW Management Company Limited | Households | 2018 |
| Making Creative Work Ltd | Professional & scientific | 2018 |
| Making More Magic Ltd | Wholesale & retail | 2018 |
| Malar Enterprise Ltd | Wholesale & retail | 2020 |
| Malc's Place Limited | Hospitality | 2025 |
| Malebox Club Ltd | Wholesale & retail | 2018 |
| Mallalieuk Ltd | Professional & scientific | 2025 |
| Mallers Ltd | Financial services | 2017 |
| Malory Freelance Limited | Professional & scientific | 2024 |
| Malyn Ltd | Real estate | 2018 |
| Mama Brown & Co Ltd | Wholesale & retail | 2018 |
| Mama Dina Ltd | Information & communication | 2023 |
| Mama Nelly's Kitchen Ltd | Hospitality | 2010 |
| Mama ZSA Ltd | Hospitality | 2024 |
| Mamdev UK Ltd | Construction | 2026 |
| Mamoks Limited | Construction | 2022 |
| Mana Arts Co CIC | Education | 2026 |
| Managing Prestige Ltd | Professional & scientific | 2025 |
| Mandore Engineering & Construction Limited | Information & communication | 2012 |
| Manifest Digital Ltd | Administrative & support | 2013 |
| Manifested Ltd | Extraterritorial | 2021 |
| Manishaa's Boutique Ltd | Wholesale & retail | 2025 |
| Manktelow Limited | Manufacturing | 2004 |
| Manoach Limited | Real estate | 2019 |
| Manor House Project Management Ltd | Professional & scientific | 2026 |
| Manor Oak Contracts Limited | Construction | 2023 |
| Manor Road Management (RTE Company) Ltd | Real estate | 2010 |
| Manorville Care Homes Ltd | Health & social care | 2011 |
| Mansell Lewis Limited | Professional & scientific | 2014 |
| Mantis Engineering & Consultants Ltd | Professional & scientific | 2016 |
| Mantle Tax Services Limited | Professional & scientific | 2018 |
| Mantra Communications UK Limited | Professional & scientific | 2014 |
| Mantz Associates Ltd | Information & communication | 2018 |
| Many Ways Solutions Limited | Professional & scientific | 2024 |
| Maoin Pensio Ltd | Real estate | 2020 |
| MAP Eternal Limited | Wholesale & retail | 2024 |
| MAP Roofing Consultancy Ltd | Construction | 2025 |
| Mapleton Close (Bromley) Freehold Limited | Real estate | 2016 |
| MAR Anne Business Limited | Wholesale & retail | 2024 |
| Maralon Recruitment Ltd | Administrative & support | 2025 |
| Marangoz Accountants Ltd | Professional & scientific | 2018 |
| Marar Consulting Ltd | Information & communication | 2021 |
| Marbles Limited | Manufacturing | 1983 |
| Marcam Limited | Arts & recreation | 2010 |
| Marcel Salloum Ltd | Manufacturing | 2013 |
| Marcelotrans Ltd | Transport & logistics | 2019 |
| Marcou Leveton Limited | Other services | 2017 |
| Marcus Bishop Associates Limited | Professional & scientific | 1995 |
| Marden Manor Management Ltd | Households | 2024 |
| Mardrew LLP | | 2024 |
| Margin Goods Group Ltd. | Wholesale & retail | 2020 |
| Marhans Group Ltd | Wholesale & retail | 2025 |
| Maria's Chocolate Ltd | Hospitality | 2023 |
| Maria’S Electrical Ltd | Wholesale & retail | 2026 |
| Marilena Piano Tuition Ltd | Education | 2023 |
| Marine Centre Limited | Manufacturing | 2021 |
| Marinstar Limited | Information & communication | 1990 |
| Marion Consulting Limited | Information & communication | 2017 |
| Maritime Construction Consultants Ltd | Professional & scientific | 2021 |
| Maritime Construction Contractor Services Ltd | Financial services | 2025 |
| Maritime Construction FX Ltd | Financial services | 2025 |
| Maritime Construction Group Ltd | Professional & scientific | 2025 |
| Maritime Construction Projects Ltd | Administrative & support | 2025 |
| Maritime Construction Training Limited | Education | 2025 |
| Maritime House (London) RTM Company Limited | Real estate | 2022 |
| Mark 1 Security Specialists Ltd | Administrative & support | 2023 |
| Mark Beaumont Ltd | Real estate | 2008 |
| Mark Chiu Creative Ltd | Professional & scientific | 2022 |
| Mark Emery Limited | Information & communication | 2009 |
| Mark Hart Real Estate Ltd | Real estate | 2019 |
| Mark Holden Motorcycles Limited | Wholesale & retail | 2023 |
| Mark Manik Limited | Manufacturing | 2004 |
| Mark Smith Construction Limited | Administrative & support | 2015 |
| Mark Yelding Limited | Administrative & support | 2024 |
| Markcorp Private Ltd | Wholesale & retail | 2015 |
| Markelytics Limited | Information & communication | 2015 |
| Market Squared Limited | Education | 2014 |
| Marketforce Services Limited | Other services | 2016 |
| Markland Mechanical Services Ltd | Construction | 2018 |
| Marklet Ltd | Hospitality | 2025 |
| Markstay Limited | Real estate | 2021 |
| Marku a Limited | Health & social care | 2013 |
| Marky Wolf Ltd | Professional & scientific | 2025 |
| Marlborough Executives Limited | Professional & scientific | 1997 |
| Marlin Lendings Ltd | Information & communication | 2024 |
| Marlo & Pierres Ltd | Construction | 2026 |
| Marmof Transform Ltd | Manufacturing | 2024 |
| Marmont Residents Management Company Limited | Real estate | 2015 |
| Marria Amir Investments Limited | Construction | 2024 |
| Marsden Grant International Limited | Professional & scientific | 1991 |
| Marshall Laurence Surveyors Ltd | Professional & scientific | 2024 |
| Marshall Street Advisors Limited | Administrative & support | 2018 |
| Marshall Street Capital Partners Limited | Administrative & support | 2018 |
| Marshall Street Consulting Limited | Administrative & support | 2018 |
| Marshall Street Equity Partners Limited | Administrative & support | 2018 |
| Marshall Street Venture Partners Limited | Administrative & support | 2018 |
| Marsons Solicitors LLP | | 2010 |