| Mantoniou Limited | Other services | 2017 |
| Manumission Holdings Ltd | Financial services | 2025 |
| MAP 01 Ltd | Information & communication | 2018 |
| MAP Property Investing Ltd | Real estate | 2018 |
| Maple Durham Estates Limited | Households | 1983 |
| Maple Orchard Management Limited | Households | 2002 |
| Maple Stephens Consultants Limited | Professional & scientific | 2011 |
| Mapleridge Care Ltd | Health & social care | 2025 |
| Mapp Properties London Limited | Construction | 2017 |
| Mapre Limited | Real estate | 2026 |
| Maral Group Limited | Wholesale & retail | 2026 |
| Maramaxos Ltd | Extraterritorial | 2020 |
| Marathon Papa Properties Ltd | Financial services | 2020 |
| Marble Arch Taverns Limited | Hospitality | 2010 |
| Marchalsey Limited | Professional & scientific | 2006 |
| Marchent Limited | Construction | 2003 |
| Marcomedia Limited | Professional & scientific | 1997 |
| Mardley Ltd | Real estate | 2020 |
| Mared Investments Limited | | 1960 |
| Marel Corporation Ltd. | Information & communication | 2017 |
| Maresfield Limited | Real estate | 1993 |
| Margot Schiemann Limited | Health & social care | 2002 |
| Maria Black Online UK Ltd | Wholesale & retail | 2021 |
| Maria Black UK Ltd | Wholesale & retail | 2018 |
| Maria Black Wholesale UK Ltd | Wholesale & retail | 2021 |
| Maria Eleftheriou Ltd | Professional & scientific | 2025 |
| Marie's Shoes Ltd | Wholesale & retail | 2010 |
| Mariella Nicholas Homes Limited | Real estate | 2020 |
| Marigold Trading Limited | Hospitality | 2012 |
| Marina Homecare Ltd | Health & social care | 2022 |
| Marion Ackerman Limited | Information & communication | 2022 |
| Maritime P Limited | Manufacturing | 1982 |
| Maritimepay Ltd | Administrative & support | 2025 |
| Mark Ballard Marine Ltd | Professional & scientific | 2024 |
| Mark Bird Building Contractors Limited | Administrative & support | 2002 |
| Mark H Limited | Wholesale & retail | 1988 |
| Mark Payne Plumbing & Heating Specialist Ltd | Construction | 2013 |
| Mark Rafferty Ltd | Information & communication | 2014 |
| Mark Steven Limited | Construction | 1987 |
| Marked by Luxury Limited | Professional & scientific | 2024 |
| Market Mews & Market Street Flats Ltd | Real estate | 2023 |
| Market Research 4 U Limited | Professional & scientific | 2020 |
| Marlborough Gardens (West) (Surbiton)Residents Association Limited | Real estate | 1962 |
| Marlos Properties Ltd | Real estate | 2022 |
| Marlport Limited | Real estate | 1998 |
| Marmalade Bear Ltd | Financial services | 2020 |
| Marney UK Limited | Real estate | 2023 |
| Marquis Wealth Management LLP | | 2009 |
| Marreddy Limited | Health & social care | 2007 |
| Marru Ltd | Financial services | 2020 |
| Mars Central Limited | Administrative & support | 2013 |
| Mars Properties Limited | Real estate | 2016 |
| Marshall K Paving (UK) Limited | Construction | 2022 |
| Marshall Recycling Limited | Professional & scientific | 2011 |
| Marshalls Homes Ltd | Real estate | 2022 |
| Martee Limited | Information & communication | 2023 |
| Martin Charles Textiles Limited | Wholesale & retail | 1995 |
| Martin Lang Limited | Professional & scientific | 2011 |
| Martin Logan Limited | Construction | 2014 |
| Martin UK Management Ltd | Real estate | 2023 |
| Martin UK Property Ltd | Real estate | 2021 |
| Martsbuild Limited | Construction | 2015 |
| Maru Design and Print Ltd | Manufacturing | 2026 |
| Marvellous Limited | Information & communication | 2001 |
| Marx Josif Ltd | Real estate | 2017 |
| Mary Construction Limited | Construction | 2017 |
| Mary KAY Temowo Logistics Ltd | Transport & logistics | 2019 |
| Mary Malde Interior Design Ltd | Professional & scientific | 2024 |
| Marzena Joseph Ltd | Wholesale & retail | 2023 |
| Masala Lounge Ltd | Hospitality | 2006 |
| Masala Mart Ltd | Wholesale & retail | 2024 |
| Mash Capital Limited | Real estate | 2023 |
| Mash Capital Management Ltd | Real estate | 2024 |
| Mash Capital Properties Ltd | Real estate | 2026 |
| Mashcam Ltd | Construction | 2018 |
| Masileo Developments Ltd | Construction | 2025 |
| Masileo Group Holdings Ltd | Financial services | 2025 |
| Masileo Property Ltd | Households | 2024 |
| Mason's Management Services Limited | Real estate | 2017 |
| Masonry Brothers Limited | Construction | 2021 |
| Massa Artz Ltd | Wholesale & retail | 2026 |
| Massive Action Coaching Ltd | Professional & scientific | 2003 |
| Master Property Construction Limited | Administrative & support | 2022 |
| Master Property Management Limited | Administrative & support | 2013 |
| Masterdent Limited | Wholesale & retail | 2000 |
| Masterfix Electrical Ltd | Construction | 2026 |
| Masters & Associates Limited | Administrative & support | 2025 |
| Masterson Leisure Holdings (MLH) Ltd | Hospitality | 2020 |
| MAT CUT Ltd | Other services | 2024 |
| Matchbook Creative Limited | Administrative & support | 2026 |
| Matchbox Jewellery Limited | Manufacturing | 2019 |
| Matchcare Limited | Health & social care | 2009 |
| Matchcost Consultants Limited | Administrative & support | 2015 |
| Matching Numbers Ltd. | Wholesale & retail | 2017 |
| Matheou Properties Ltd | Real estate | 2024 |
| Mathilde Fruit Limited | Hospitality | 2025 |
| Mathologika Limited | Information & communication | 2025 |
| Maths Base Limited | Education | 2020 |
| Maths Sign Solutions CIC | Education | 2024 |
| Maths Talking Buddies Ltd | Education | 2013 |