| Moreton Investment Research Limited | Professional & scientific | 2025 |
| Moreton Street Partnership Limited | Professional & scientific | 1979 |
| Morgan & Family UK Ltd | Wholesale & retail | 2018 |
| Moringa TZ Limited | Wholesale & retail | 2019 |
| Morpheus Solutions Ltd | Wholesale & retail | 2023 |
| Mort & Stroud Limited | Construction | 2003 |
| Mortgage Decisions Limited | Financial services | 2010 |
| Mortgage Required (Southampton) Limited | Financial services | 2015 |
| Mortimers Farm Developments Ltd | Construction | 2021 |
| Mortimers Farm Management Co Ltd | Construction | 2024 |
| MOS Collection Ltd | Wholesale & retail | 2024 |
| Mosaic Financial Consulting Limited | Real estate | 2010 |
| Motor Heads Limited | Other services | 2022 |
| Motsu Limited | Real estate | 2018 |
| Mould Tool Services (Hampshire) Limited | Manufacturing | 2015 |
| Moura Courier Services Ltd | Transport & logistics | 2021 |
| Mous Products Ltd | Wholesale & retail | 2015 |
| Mousehole Press Ltd | Information & communication | 2020 |
| Movement, Sound & Lighting Limited | Wholesale & retail | 1998 |
| Movewell at Home Physiotherapy Ltd | Health & social care | 2026 |
| Movora Health Ltd | Health & social care | 2026 |
| Moxhams Limited | Real estate | 1998 |
| Mozzo Coffee Limited | Wholesale & retail | 2005 |
| Mozzo Limited | Wholesale & retail | 2007 |
| Mozzo Tecnico LLP | | 2012 |
| Mozzo World Limited | Real estate | 2018 |
| MP Analytics Limited | Administrative & support | 2021 |
| MP Lightbown & SON Limited | Transport & logistics | 2012 |
| MP Mechanical Limited | Manufacturing | 2021 |
| MP Refinishing Ltd | Construction | 2025 |
| Mpca Ltd | Extraterritorial | 1985 |
| MPH IT Services Ltd | Information & communication | 2011 |
| MPS Facility Services Limited | Agriculture & fishing | 2015 |
| MPT Sparky Ltd | Administrative & support | 2025 |
| Mpumi Consultancy Limited | Health & social care | 2011 |
| MR Treehouse and MR Zipwire Ltd | Construction | 2017 |
| MRG Projects Limited | Construction | 2018 |
| MRJ Digital Ltd | Information & communication | 2022 |
| MRT Land Holdings Ltd | Professional & scientific | 2009 |
| Mrtalalaa Entertainment Ltd | Information & communication | 2024 |
| MSC350 Limited | Professional & scientific | 2017 |
| Msel Services Limited | Construction | 2017 |
| Msingi WA Sanaa Ltd | Arts & recreation | 2021 |
| MSK Health Clinics Limited | Health & social care | 2025 |
| MSK Pain Clinics LLP | | 2025 |
| MSN Investments Ltd | Real estate | 2023 |
| MSN Real Estate Limited | Real estate | 2025 |
| MSR Holding Group Ltd | Financial services | 2025 |
| MSW Thames Valley Limited | Professional & scientific | 2013 |
| MTC Landcare Services Ltd | Agriculture & fishing | 2020 |
| MTR Properties Investment Ltd | Real estate | 2025 |
| Mudlarks Theatre Limited | Arts & recreation | 2019 |
| Mugo Commerce Ltd | Wholesale & retail | 2026 |
| Mulberry Insurance Services Limited | Financial services | 1993 |
| Multi-Tip Limited | Wholesale & retail | 2001 |
| Multiboard Ltd | Information & communication | 2024 |
| Mundy Estates Ltd | Hospitality | 2020 |
| Murfittsmith Limited | Real estate | 2021 |
| Murphy & Sons Properties Limited | Real estate | 2023 |
| Murphy Brickwork Limited | Construction | 2012 |
| Muscle Cafe Ltd | Wholesale & retail | 2025 |
| Mustafa Family Ltd | Administrative & support | 2018 |
| Mwiseman TM Ltd | Construction | 2023 |
| MWT Holdings UK Ltd | Wholesale & retail | 2024 |
| My Claim Limited | Extraterritorial | 2011 |
| My GAS Ltd | Construction | 2026 |
| My Invoice Limited | Administrative & support | 2014 |
| My Marine Ltd | Manufacturing | 2015 |
| My MED Clinic Limited | Wholesale & retail | 2023 |
| My Oak Frame Ltd | Manufacturing | 2021 |
| My Planning App LLP | | 2017 |
| My Planning Ltd | Professional & scientific | 2021 |
| My Training Records Ltd | Education | 2020 |
| Mybridity Limited | Construction | 2023 |
| Mymedsec Ltd | Administrative & support | 2026 |
| Mysy Limited | Real estate | 2018 |
| N Balbido Aviation Services Ltd | Manufacturing | 2017 |
| N Mugariri Ltd | Construction | 2019 |
| N P Joyce Plastering Limited | Construction | 2014 |
| N Page Plastering Ltd | Construction | 2023 |
| N-Tek Door Solutions Ltd | Construction | 2022 |
| N.C. Roofing and Building (Southern) Ltd | Construction | 2026 |
| N.H.Willis & Co.Limited | Real estate | 1951 |
| N.R. Trickett (Developments) Limited | Construction | 1958 |
| N2 END Ltd | Real estate | 2026 |
| Na's Bar Ltd | Hospitality | 2023 |
| Nacra UK Limited | Wholesale & retail | 2008 |
| Nael Chauffeurs Ltd | Transport & logistics | 2023 |
| Nails by Priya Limited | Other services | 2024 |
| Nalpat Ltd | Wholesale & retail | 2011 |
| Nanak Nivas Holdings Ltd | Financial services | 2026 |
| Nash Golf Holdings Ltd | Financial services | 2024 |
| Nash Golf Limited | Wholesale & retail | 2012 |
| Nasreen Fareed Limited | Hospitality | 2015 |
| NAT Tara Thai Massage & Therapy Ltd | Health & social care | 2022 |
| Natalia Faith Grace Foundation Ltd | Administrative & support | 2015 |
| National Association of the Launderette Industry Limited (the) | Other services | 1956 |
| National Fasteners Ltd | Wholesale & retail | 2015 |
| Nationwide Roofing and Cladding (Holdings) Ltd | Professional & scientific | 2021 |
| Nationwide Roofing and Cladding Ltd | Construction | 2011 |