| Manhar Property (Sidcup) Limited | Construction | 2015 |
| Manna Lodge Ltd | Real estate | 2023 |
| Manna London Ltd | Administrative & support | 2020 |
| Manna Property Search Limited | Real estate | 2025 |
| Manning Austin Property Consultants Limited | Professional & scientific | 2017 |
| Manspeed Transport Limited | Transport & logistics | 1997 |
| Mantra Interiors Limited | Wholesale & retail | 2010 |
| Manwood Limited | Professional & scientific | 2014 |
| Maple Leaf Mortgages Limited | Financial services | 2021 |
| Maple Property Investments LLP | | 2015 |
| Maple Wood Grange Management Company Limited | Households | 2012 |
| Marc Burton Services Ltd | Construction | 2018 |
| Marco Polo Hair Limited | Other services | 2006 |
| Marcus Advisory Ltd | Professional & scientific | 2015 |
| Marcus Williams Design Limited | Professional & scientific | 2011 |
| Marden Bakery Limited | Hospitality | 2022 |
| Marden Midnight Spice Ltd | Hospitality | 2018 |
| Maresfield Park Developments Limited | Construction | 2025 |
| Margrove Properties and Lettings Limited | Real estate | 2024 |
| Mari Healthcare Limited | Other services | 2016 |
| Mariabilingualcounsellor Ltd | Health & social care | 2024 |
| Mark Barnes Property Ltd | Real estate | 2026 |
| Mark COX Anaesthesia Ltd | Health & social care | 2020 |
| Mark Haskett Accounts Limited | Professional & scientific | 2010 |
| Mark Selden Limited | Professional & scientific | 2010 |
| Mark Walton Decorators Limited | Construction | 2011 |
| Market Close (Ashburton) Management Company Limited | Real estate | 2013 |
| Market Trend Interactive Solution Limited | Real estate | 2022 |
| Marketing and More Consulting Services Ltd | Professional & scientific | 2016 |
| Marketing Medicines OTC Ltd | Professional & scientific | 2014 |
| Markizmo Limited | Information & communication | 2013 |
| Marlew Consultancy Ltd | Real estate | 2019 |
| Marly Trading Ltd | Wholesale & retail | 2021 |
| Marmalade Film and Media Limited | Information & communication | 2008 |
| Marmaris Barbershop Kent Ltd | Other services | 2025 |
| Marneth Limited | Real estate | 2004 |
| Marque 212 Limited | Information & communication | 2017 |
| Marque 213 Limited | Information & communication | 2017 |
| Marshall Associates Limited | Professional & scientific | 2002 |
| Marshall Pembroke Limited | Professional & scientific | 2026 |
| Marta's Place Limited | Other services | 2010 |
| Martin's View Property Management Company Limited | Households | 2022 |
| Martinez 4 Hair Ltd | Other services | 2009 |
| Marton Residential Estates Limited | Real estate | 2007 |
| Marx Limited | Real estate | 2025 |
| Marx Medical Limited | Health & social care | 2025 |
| Mason Capital Development Limited | Construction | 2016 |
| Mason Capital Limited | Real estate | 2014 |
| Mason Holdings Limited | Financial services | 2016 |
| Masseys Enforcement Ltd. | Administrative & support | 2017 |
| Massonetto Express Ltd | Transport & logistics | 2019 |
| Master & Groomsman Limited | Wholesale & retail | 2008 |
| Master Andrew Ltd | Wholesale & retail | 2018 |
| Masterplan (Sussex) Limited | Administrative & support | 1988 |
| Masters of Malt Limited | Manufacturing | 2018 |
| Matrac Ecommerce Ltd | Wholesale & retail | 2025 |
| Mattacol Limited | Manufacturing | 2006 |
| Mattch Consultancy Services Ltd | Professional & scientific | 2020 |
| Mature Movers Limited | Professional & scientific | 2020 |
| Maverick Brands Limited | Manufacturing | 2018 |
| Maverick Drinks Limited | Manufacturing | 2018 |
| Maverick Spirits Limited | Manufacturing | 2018 |
| Maximum Living Limited | Professional & scientific | 2017 |
| Maximus Technology Limited | Information & communication | 2023 |
| Maxitrak Limited | Manufacturing | 1988 |
| Mayer Medical Services Limited | Other services | 2019 |
| Mayfair Sports Capital Ltd | Professional & scientific | 2026 |
| MB Electrical Services (South East) Ltd | Construction | 2019 |
| MB Media Advisory Limited | Professional & scientific | 2019 |
| MB Property Creations Limited | Construction | 2019 |
| MB Steel Group Limited | Construction | 2025 |
| MBT Insight Limited | Information & communication | 2022 |
| MC Hotel Consultants Ltd | Professional & scientific | 2020 |
| MC2 Group Ltd | Real estate | 2025 |
| Mcarthur Contracts Ltd | Construction | 2025 |
| Mcbrien Consulting Ltd | Administrative & support | 2017 |
| Mcclune Limited | Professional & scientific | 2006 |
| Mccullough Development Limited | Construction | 2009 |
| MCF Residents Association Limited | Households | 2023 |
| Mcgonigle Services Ltd | Other services | 2022 |
| Mcintosh Consultancy Limited | Professional & scientific | 2020 |
| MCK Solutions Limited | Information & communication | 2011 |
| Mckenzie Surgical Limited | Health & social care | 2021 |
| MCL Sporting Goods Consultancy Company Limited | Professional & scientific | 2023 |
| Mclintock Consultants Ltd | Professional & scientific | 2023 |
| MCM Services Fitted Bedrooms Ltd | Construction | 2026 |
| MCN Care Services Limited | Health & social care | 2019 |
| Mcpneuro Ltd | Health & social care | 2021 |
| Mcqueen Hair & Beauty Limited | Other services | 2008 |
| Mcveigh Medical Ltd | Health & social care | 2023 |
| MD Accountancy Team Ltd | Professional & scientific | 2012 |
| MD Health London Limited | Administrative & support | 2015 |
| MD Stodell Ltd | Health & social care | 2022 |
| MDG Ashley Investments Limited | Construction | 2020 |
| Mdlg Fitness Ltd | Arts & recreation | 2025 |
| MDN Developments Limited | Construction | 2003 |
| ME19 Propco Ltd | Real estate | 2026 |
| Meat'Ing UK Limited | Wholesale & retail | 2012 |
| MEC Consultancy Ltd | Professional & scientific | 2014 |
| Mediapod Limited | Manufacturing | 2010 |