| MDS Renovations Ltd | Construction | 2014 |
| Meadow Farm Produce Limited | Wholesale & retail | 1995 |
| Measured Energy Efficiency Solutions Ltd | Professional & scientific | 2025 |
| Measurement Solutions Limited | Wholesale & retail | 1998 |
| Mechanical Knight Services Ltd | Wholesale & retail | 2022 |
| Melt & Motion Ltd | Information & communication | 2025 |
| Merchant Traveller Ltd | Information & communication | 2024 |
| Mercurio Limited | Wholesale & retail | 2005 |
| Merida Properties Ltd | Real estate | 2025 |
| Meristem Services Ltd | Administrative & support | 2024 |
| Metagalactic Holding Ltd | Financial services | 2016 |
| MG Fusion Limited | Construction | 2018 |
| Michael Toner Ltd | Extraterritorial | 2024 |
| Midland Marts Limited | Extraterritorial | 2011 |
| Midnight Digital Group Ltd | Professional & scientific | 2022 |
| Mighty Fine Entertainment Limited | Professional & scientific | 2012 |
| Mighty Fine Events Ltd | Arts & recreation | 2023 |
| Mighty Fine Live Production Ltd | Administrative & support | 2024 |
| MIH Major Events Ltd | Professional & scientific | 2022 |
| Miirah Ltd | Manufacturing | 2024 |
| Millennium Training Consultants Ltd | Administrative & support | 2011 |
| Mills Carpentry Group Ltd | Financial services | 2025 |
| Mills Carpentry, Building & Maintenance Limited | Construction | 2008 |
| Mills Commercials & Fire Doors Limited | Public administration | 2024 |
| Milton Buzzard Motor Cycle Club Limited | Other services | 2010 |
| Milton Keynes Property Maintenance Services Ltd | Construction | 2025 |
| Mindbridge Education Group Limited | Public administration | 2025 |
| Minimal Holdings Limited | Professional & scientific | 2004 |
| Missenden Electrical Ltd. | Construction | 2007 |
| Mitchell & Gray Developments Ltd | Construction | 2017 |
| Mitchell & Gray Holdings Ltd | Financial services | 2017 |
| Mitchell Information Technology LLP | | 2012 |
| Mitchell Luxury Cars Ltd | Wholesale & retail | 2010 |
| MJY Security Systems Limited | Administrative & support | 2008 |
| MK Blaster Ltd | Administrative & support | 2021 |
| MK Ninjas JJ Ltd | Arts & recreation | 2025 |
| MKG Property Maintenance LLP | | 2026 |
| MLW Rigging Services Ltd | Information & communication | 2025 |
| Mmjh Holdings Limited | Financial services | 2020 |
| MML Solvex Ltd | Professional & scientific | 2023 |
| Modaha Ltd | Wholesale & retail | 2025 |
| Mode Holdings Ltd | Real estate | 2015 |
| Mode Performance Limited | Wholesale & retail | 2008 |
| Mode Racing Limited | Wholesale & retail | 2015 |
| Modena Silverstone Limited | Extraterritorial | 2016 |
| Moghul Towcester Ltd | Hospitality | 2025 |
| Mollyandco Limited | Wholesale & retail | 2017 |
| Monarch Scaffolding Limited | Construction | 2024 |
| Monastery Lakes Farm Limited | Agriculture & fishing | 2026 |
| Monolith Hospitality Consulting Ltd | Other services | 2022 |
| Monstera Holdings Limited | Extraterritorial | 2018 |
| Monty Foods Ltd | Manufacturing | 2023 |
| Moolife Limited | Wholesale & retail | 2007 |
| Moor Pond Piece Residents Association Limited | Households | 2002 |
| Moore Inspiration Developments Ltd | Construction | 2020 |
| Moore Inspiration Ltd | Construction | 2009 |
| Moorgate Broker Network Ltd | Extraterritorial | 2024 |
| Moorgate Business Protection Ltd | Financial services | 2022 |
| Moorgate Finance Capital Ltd | Administrative & support | 2020 |
| Moorgate Finance Limited | Financial services | 2014 |
| Moorgate Finance Management LLP | | 2023 |
| Moorgate Group Holdings Limited | Financial services | 2017 |
| Moorgate Investments Limited | Real estate | 2017 |
| Moorgate Mortgage Brokers Ltd | Financial services | 2023 |
| Morganics Hemp UK Ltd | Manufacturing | 2024 |
| Mortgage Smart Limited | Financial services | 2020 |
| Morville Street Developments Limited | Construction | 2020 |
| Motormedia Automotive Limited | Wholesale & retail | 2004 |
| Motorsport NDT Limited | Professional & scientific | 2022 |
| Motorsports Hall of Fame Ltd | Arts & recreation | 2010 |
| Mottisfont Development Group Limited | Professional & scientific | 2020 |
| Moulton Contracting Ltd | Construction | 2025 |
| Mountain ASH Software Ltd | Information & communication | 2026 |
| Move OR DIE Limited | Professional & scientific | 2002 |
| MP Devco Limited | Real estate | 2010 |
| MS Optimal Ltd | Information & communication | 2019 |
| MSP Dark Web Ltd | Information & communication | 2021 |
| MTD Software Limited | Information & communication | 2023 |
| MTO Furniture Ltd | Information & communication | 2021 |
| Mullen Scaffolding Ltd | Construction | 2025 |
| Mullen Security Ltd | Administrative & support | 2022 |
| Multi-Lingual International Recruitment Limited | Administrative & support | 2012 |
| Murdoch + Pitman Devco Ltd | Construction | 2021 |
| Mursley Motor Sales Ltd | Wholesale & retail | 2024 |
| Muscaria Ltd | Extraterritorial | 2019 |
| Music With Meaning CIC | Arts & recreation | 2025 |
| MW Holdings Limited | Real estate | 2022 |
| My Travel Marketing Ltd | Information & communication | 2023 |
| N & B Engineering LP | | 1998 |
| N F Rights Limited | Information & communication | 2022 |
| N Gray & Sons Limited | Construction | 2012 |
| N. Huckle & Sons Garden Services Limited | Administrative & support | 2021 |
| Nash Wealth Management Ltd | Financial services | 2019 |
| Nathalie Mcgloin Racing Ltd | Arts & recreation | 2016 |
| Nationwide Car Parks Limited | Real estate | 2012 |
| Natural Capital Solutions Ltd | Professional & scientific | 2015 |
| Natural Creative Limited | Professional & scientific | 2023 |
| NBS Car Parts Ltd | Wholesale & retail | 2015 |
| NC Hamilton Limited | Households | 2020 |
| NDC Consultancy Ltd | Administrative & support | 2018 |