| Mangrios Limited | Wholesale & retail | 2023 |
| Maple Leaf Therapy Ltd | Health & social care | 2020 |
| Mariano's Pizzeria & Kebab Ltd | Hospitality | 2025 |
| Marine Lake Property Limited | Real estate | 2018 |
| Mariner CAY Ltd | Construction | 2008 |
| Mark Sims Education Consultancy Ltd | Education | 2023 |
| Martin Hayward Limited | Professional & scientific | 2004 |
| MAS Capital Ltd | Other services | 2017 |
| Mason Facades Maintenance Limited | Construction | 2023 |
| Masons Property Holdings Ltd | Real estate | 2015 |
| Masons Self Storage Ltd | Real estate | 2003 |
| Master Lettings Ltd. | Real estate | 2017 |
| Master Lettings Management Ltd | Construction | 2022 |
| MATBURCHSYSENGP3M Ltd | Professional & scientific | 2020 |
| Matei Alexandru Ltd | Transport & logistics | 2014 |
| Matt Hughes Sound Ltd | Information & communication | 2022 |
| Matt J Collins Ltd | Financial services | 2014 |
| Matt Williams Services Ltd | Manufacturing | 2019 |
| Matthew Bohun Lighting Ltd | Arts & recreation | 2023 |
| Maximan Ltd | Manufacturing | 2007 |
| Maximise Property Management Ltd | Real estate | 2021 |
| Mbkf Associates Ltd | Other services | 2024 |
| MC Flooring & Carpets Ltd | Wholesale & retail | 2022 |
| MC Value Motors Ltd | Wholesale & retail | 2026 |
| MCC Automotive Sales Ltd | Wholesale & retail | 2025 |
| MCC Recovery Ltd | Transport & logistics | 2025 |
| Mclaggon Engineering Ltd | Construction | 2023 |
| MDK Restaurants Ltd | Hospitality | 2025 |
| MDV Holdings Limited | Wholesale & retail | 2019 |
| Meat and Greek Festivals Limited | Hospitality | 2023 |
| Med-Orator Ltd | Education | 2021 |
| Mediamagick Ltd | Manufacturing | 2023 |
| Megan Publishing Services Limited | Information & communication | 2025 |
| MEI SUM Barry Ltd | Hospitality | 2025 |
| Melania Logistics Ltd | Transport & logistics | 2021 |
| Melin Limited | Health & social care | 2016 |
| Melovibes Ltd | Wholesale & retail | 2022 |
| Merricks Private Transport Contractors Limited | Transport & logistics | 2004 |
| Mershbrook Developments Limited | Construction | 2017 |
| Mewstone Consultants Limited | Information & communication | 2017 |
| MGJ Wholesale Ltd | Wholesale & retail | 2025 |
| Miaayla Ltd | Wholesale & retail | 2022 |
| MIC Check ENT Ltd | Administrative & support | 2025 |
| Michaelston Estates Limited | Real estate | 1999 |
| Michelle Newman Limited | Professional & scientific | 2016 |
| Microplay Electronics Limited | | 1987 |
| Mihai Painting Ltd | Wholesale & retail | 2018 |
| Mike Coles Storyboard Studio Ltd | Information & communication | 2020 |
| Mike DEE Landscape and Gardening Services Ltd | Administrative & support | 2025 |
| Mike Guthrie Building Solutions Limited | Construction | 2023 |
| Mike Nash Motors Limited | | 1960 |
| Mike Waudby Creative Ltd | Professional & scientific | 2019 |
| Mildef Limited | Manufacturing | 2006 |
| Millwood Bowling Club Ltd | Arts & recreation | 2019 |
| Millwood Properties Ltd | Real estate | 2025 |
| Mimimay Ltd | Other services | 2025 |
| Mind Crafted Wellbeing Ltd | Other services | 2022 |
| Mind in the Vale of Glamorgan | Health & social care | 1996 |
| Miss Bubbles Ltd | Administrative & support | 2025 |
| Miss Holmes Ltd | Wholesale & retail | 2017 |
| Miss Katherine & Christina Beauty Ltd | Other services | 2021 |
| Miss Pennies Limited | Hospitality | 2025 |
| Misschips Ltd | Hospitality | 2023 |
| Mitchell Lighting Associates Ltd | Arts & recreation | 2016 |
| Mitten Corporation Limited | Information & communication | 2018 |
| Mivi Ltd | Professional & scientific | 2023 |
| MJ Commercial Services Limited | Manufacturing | 2016 |
| Mjfl Properties Ltd | Real estate | 2023 |
| MJH Executive Cars Ltd | Transport & logistics | 2024 |
| Moct Property Investment Ltd | Real estate | 2025 |
| Mojo Animal Services Ltd | Professional & scientific | 2021 |
| Moloko House Ltd | Hospitality | 2023 |
| Monolith Group Holdings Limited | Professional & scientific | 2020 |
| Monty and Vito’S Diner Limited | Hospitality | 2018 |
| Moonbeam Services Limited | Administrative & support | 2017 |
| Moorlynch Limited | Households | 2021 |
| Moors Motors Limited | Wholesale & retail | 2025 |
| MOR Cleaning Limited | Administrative & support | 2020 |
| Morden's Bakery & Cafe Ltd | Hospitality | 2025 |
| Mordovia Limited | Professional & scientific | 2010 |
| More Than Flags and Rainbows CIC | Education | 2024 |
| Morgan Carter Investments Ltd | Real estate | 2018 |
| Morgan Civil Engineering Limited | Administrative & support | 2016 |
| Morgan Walsh Consultancy Limited | Information & communication | 2006 |
| Motive Contracts Limited | Construction | 1996 |
| MPD (UK) Limited | Professional & scientific | 1989 |
| Mptrade Ltd | Wholesale & retail | 2024 |
| MR. Digby's 1954 Ltd. | Hospitality | 2016 |
| MRC Automotive Ltd | Wholesale & retail | 2024 |
| MRW Aircraft Engineer Ltd | Manufacturing | 2022 |
| MS Aero Ltd | Manufacturing | 2026 |
| MS Equity Limited | Professional & scientific | 2020 |
| MSS Property Holdings Ltd | Real estate | 2015 |
| Muscle Cat Ltd. | Information & communication | 2024 |
| My Construct Ltd | Construction | 2025 |
| MÔR a Sawna Limited | Other services | 2024 |
| N & P Auto Car Ltd | Wholesale & retail | 2019 |
| N Harvey Transport Ltd | Transport & logistics | 2013 |
| N James Electrical Services Ltd | Construction | 2022 |
| N S Marine Consultants Limited | Professional & scientific | 2012 |