| Mimosa Investments Limited | Financial services | 2019 |
| Minerva-Site Solutions Limited | Professional & scientific | 2016 |
| Minibus Executive Travel Limited | Real estate | 2001 |
| MKL Careers Limited | Administrative & support | 2020 |
| MLD GAS and Construction Services Ltd | Construction | 2023 |
| MNC Designcare Services Ltd | Administrative & support | 2021 |
| Moffat Davis Electrical Contractors Ltd | Construction | 2013 |
| Moffat Davis Holdings Limited | Professional & scientific | 2025 |
| Moir Management Services Ltd | Extraterritorial | 2005 |
| Molior Building Limited | Construction | 2018 |
| Molior Projects Limited | Professional & scientific | 2012 |
| Monaco Joinery Services Ltd | Construction | 2010 |
| Mondego Labs Ltd | Information & communication | 2025 |
| Money Stocker Ltd | Information & communication | 2025 |
| Monkwearmouth Development Limited | Construction | 2021 |
| Moor Park Capital Limited | Real estate | 2018 |
| MOS Projects Ltd | Construction | 2023 |
| Mountford Management Services Limited | Professional & scientific | 1996 |
| MP Testing Limited | Information & communication | 2012 |
| MPC Civil UK Limited | Professional & scientific | 2023 |
| Mshaker Ltd | Health & social care | 2021 |
| MST Market Solutions Ltd | Administrative & support | 2024 |
| MT UK Holding Ltd | Professional & scientific | 2024 |
| MTR Planning Limited | Professional & scientific | 2014 |
| Mulberry Property Limited | Real estate | 1999 |
| Multicore Pro Wire Limited | Construction | 2017 |
| Munch Broz Ltd | Hospitality | 2022 |
| Munnelly Group Ltd | Professional & scientific | 2005 |
| Munnelly LLP | | 2007 |
| Munnelly Support Services Limited | Construction | 1982 |
| Music Gym Academy C.I.C. | Education | 2023 |
| Muta's Sports & Co. Ltd | Education | 2021 |
| MX Distributions Ltd | Wholesale & retail | 2025 |
| Mylton Technical Limited | Administrative & support | 2022 |
| Mynydd Brombil Holdings Limited | Professional & scientific | 2012 |
| Mynydd Brombil Limited | Energy | 2012 |
| Mynydd Maen Wind Limited | Energy | 2023 |
| Mynydd Portref Holdings Limited | Professional & scientific | 2012 |
| Mynydd Portref Windfarm Limited | Energy | 2012 |
| Mysa Life Limited | Wholesale & retail | 2025 |
| N & N Electrical Services Ltd | Construction | 2013 |
| NA & AI Solutions Limited | Information & communication | 2019 |
| Nala Developments Limited | Professional & scientific | 2018 |
| Nash’S Sugar Bloom Ltd | Hospitality | 2026 |
| Natura Food Ingredients Limited | Wholesale & retail | 1999 |
| Natural Features Aesthetics Ltd | Other services | 2021 |
| Naylor Hawkins Ltd | Construction | 2019 |
| NEAT2EAT CIC | Hospitality | 2020 |
| New Albion Wind Limited | Energy | 2012 |
| New Horizons ICT Limited | Professional & scientific | 2018 |
| Newarthill Limited | Professional & scientific | 1972 |
| Newton Ferrers Solar Limited | Energy | 2012 |
| Newview Press Limited | Manufacturing | 2008 |
| NEX1 Autos Limited | Wholesale & retail | 2023 |
| Nicholls Media Limited | Information & communication | 2020 |
| Nick Dunn Consulting Limited | Information & communication | 2014 |
| Nicolla Contractors Ltd | Construction | 2023 |
| Nifflewigs Ltd | Professional & scientific | 2022 |
| Nikki Avron Ltd | Administrative & support | 2017 |
| Nippout Limited | Administrative & support | 2018 |
| Nissel House (Freehold) Limited | Households | 2024 |
| NJ Price Property Ltd | Real estate | 2026 |
| Nomarra Limited | Other services | 2025 |
| North London Blinds Ltd | Construction | 2021 |
| Northern Hydropower Holdings Limited | Energy | 2017 |
| Northern Hydropower Limited | Energy | 2015 |
| Nostalgia Electronics Ltd | Manufacturing | 2018 |
| Novem London Ltd | Wholesale & retail | 2025 |
| NSD 2 Limited | Professional & scientific | 2014 |
| Nulogic Group Limited | Financial services | 2025 |
| Numbers Farm Residents Limited | Households | 2002 |
| Nuneham Energy Limited | Energy | 2023 |
| O'Connell Specialist Recruitment UK Limited | Administrative & support | 2024 |
| Oak Court Estates (Langstone,Mon.) Limited | Construction | 1966 |
| Oakshot Contracting Ltd. | Agriculture & fishing | 2024 |
| Oakus Developments Limited | Construction | 2002 |
| OC Maintenance Engineering Ltd | Manufacturing | 2019 |
| Ocatra Limited | Professional & scientific | 2004 |
| Odglobal Limited | Other services | 2024 |
| Oedsib Limited | Wholesale & retail | 2021 |
| Office Support Services (Management) Limited | Administrative & support | 2013 |
| OH9 Print + Design Ltd | Manufacturing | 2021 |
| Old Shink Ltd | Construction | 2017 |
| Olivia Leacock Limited | Professional & scientific | 2022 |
| Olix Limited | Wholesale & retail | 2025 |
| One Sports and Entertainment Ltd | Professional & scientific | 2020 |
| Opengrove Properties Limited | Real estate | 2017 |
| Optimal Limited | Real estate | 1994 |
| Optimised Risk Services Ltd | Administrative & support | 2024 |
| Orbital Data Centres Limited | Professional & scientific | 2025 |
| Orbital DC Limited | Construction | 2026 |
| Orchard Alexandra Limited | Real estate | 2020 |
| Orchard END Holdings Limited | Professional & scientific | 2012 |
| Orchard END Windfarm Limited | Energy | 2010 |
| Orgaihub Ltd | Information & communication | 2025 |
| Osborn & Co LLP | | 2011 |
| Osha Property Ltd | Real estate | 2023 |
| OSP Consulting Ltd | Professional & scientific | 2025 |
| Outlet Group Ltd | Wholesale & retail | 2021 |
| Overlay Events Ltd | Professional & scientific | 2012 |