| Montgomery Financial Ltd | Administrative & support | 2009 |
| Monument PS Limited | Real estate | 2025 |
| Moor Strategy Limited | Professional & scientific | 2017 |
| Morgan Chimney Sweeps Ltd | Other services | 2014 |
| Morris Advisory Ltd | Professional & scientific | 2025 |
| Morston Trading Ltd | Transport & logistics | 2024 |
| Motorsportwoman CIC | Information & communication | 2025 |
| Mpathy Apps CIC | Information & communication | 2022 |
| MPH Heating Services Ltd | Construction | 2015 |
| MS Comms Services Limited | Information & communication | 2016 |
| MSE Customs Limited | Transport & logistics | 2023 |
| MSE Supply Chain Solutions Limited | Transport & logistics | 2026 |
| MSK Environmental Services Limited | Transport & logistics | 2019 |
| Mtkn International Ltd | Wholesale & retail | 2025 |
| MTR Creative Ltd | Professional & scientific | 2018 |
| Muddy Lotus Ltd | Information & communication | 2024 |
| Munch Baits Ltd | Wholesale & retail | 2011 |
| Munchkin Entertainment Limited | Arts & recreation | 2014 |
| Munden One Limited | Professional & scientific | 2022 |
| Muscava Limited | Manufacturing | 2011 |
| Music Bunker Limited | Information & communication | 2010 |
| Musley Lane (Freehold) Limited | Households | 2025 |
| Mustang Maniac Limited | Wholesale & retail | 2008 |
| Mustard Builders Ltd | Construction | 2021 |
| MW Film Services Ltd | Arts & recreation | 2026 |
| Mwconversations Limited | Health & social care | 2017 |
| MWP London Limited | Construction | 2022 |
| My Payroll Bureau Ltd | Professional & scientific | 2021 |
| Myddleton Maintenance Services Ltd | Administrative & support | 1998 |
| Myddleton Service Solutions Ltd | Administrative & support | 2022 |
| Mylnefield Investments & Consulting Limited | Professional & scientific | 2021 |
| Myriad Aviation Consulting Limited | Transport & logistics | 2003 |
| N Armes & Co Limited | Professional & scientific | 2005 |
| N J Caves Limited | Construction | 2011 |
| N&K BSE Ltd | Hospitality | 2024 |
| N.C. Pallett Nurseries Limited | Administrative & support | 1963 |
| N.C.Q. Consulting Limited | Real estate | 2002 |
| N.E Carpentry Ltd | Construction | 2021 |
| N21 Property Investments Limited | Real estate | 2019 |
| Nags Head Exclusive Ltd | Hospitality | 2025 |
| Nags Head LH Ltd | Hospitality | 2025 |
| Natalie & MAX Photo and Films Ltd. | Professional & scientific | 2023 |
| Nathanael Lloyd Ltd | Financial services | 2026 |
| National CM Limited | Professional & scientific | 2017 |
| Nattori Limited | Extraterritorial | 2013 |
| Navida Hunter Account Services and Project Management Limited | Professional & scientific | 2017 |
| Ncskin Limited | Wholesale & retail | 2021 |
| Needles and Creams Limited | Other services | 2023 |
| Neha Brow Bar Ltd | Other services | 2024 |
| Neil James Cloud Accounting Limited | Administrative & support | 2017 |
| Neon Velo Limited | Administrative & support | 2012 |
| New Energy Matrix UK Ltd | Information & communication | 1990 |
| New Marler Management Limited | Households | 1982 |
| New River Corporate Finance LLP | | 2009 |
| Next STOP1 Removals Limited | Transport & logistics | 2025 |
| Nexum Ltd | Professional & scientific | 2020 |
| Nexus Vape Marketing Ltd | Professional & scientific | 2021 |
| NFS Restaurant Technology Limited | Information & communication | 2008 |
| NFS Technology Limited | Real estate | 2021 |
| NGM Technology Advisory Ltd | Information & communication | 2026 |
| Niche Trading Limited | Administrative & support | 2013 |
| Nicole Does Digital Limited | Administrative & support | 2024 |
| NIK Evans Ltd | Construction | 2020 |
| Ninety Degrees Ltd | Professional & scientific | 2018 |
| NIX Communications Group Limited | Extraterritorial | 2020 |
| NIX Managed Print Limited | Extraterritorial | 2020 |
| NIX Networks Limited | Other services | 2019 |
| NLH & P Limited | Construction | 2019 |
| Nlhp Limited | Construction | 2017 |
| NMC Films Ltd | Information & communication | 2023 |
| NO Faff HR Ltd | Administrative & support | 2026 |
| NO Goats Limited | Administrative & support | 2005 |
| NO.23 Aesthetics Ltd | Other services | 2025 |
| Nook Residents Association Limited(The) | Professional & scientific | 1985 |
| North Hertfordshire Academy Ltd | Education | 2024 |
| North London Finance Company Limited | Financial services | 2012 |
| North London Glass & Glazing Limited | Construction | 2000 |
| Norton Family Limited | Wholesale & retail | 2018 |
| Nourish, Connect, Grow CIC | Education | 2026 |
| Novagem Limited | Administrative & support | 1989 |
| Novus Engineers Ltd | Construction | 2024 |
| NOW Training Limited | Other services | 1997 |
| NPH Holdings Ltd | Financial services | 2019 |
| NU Chef Ltd | Hospitality | 2013 |
| Nugent Limited | Extraterritorial | 2008 |
| Nuthampstead Airfield Associates Limited | Transport & logistics | 1991 |
| Nutley Ltd | Other services | 2020 |
| Nutribeaut Limited | Wholesale & retail | 2025 |
| NVM Properties Limited | Construction | 2025 |
| Nxtc Group Ltd | Information & communication | 2026 |
| O&G Consulting Ltd | Construction | 2024 |
| O'Connor Partitions Ltd | Construction | 2005 |
| O'Donnell Management Consultants Ltd | Professional & scientific | 2023 |
| O. Bass Ltd | Arts & recreation | 2023 |
| Oak & Vale Limited | Construction | 2026 |
| Oakleaf Solutions Tree Care Ltd | Agriculture & fishing | 2025 |
| Oakley Overland Ltd | Manufacturing | 2023 |
| Oaktree Bioscience Limited | Professional & scientific | 2017 |
| Oakwood Asset Management Limited Liability Partnership | | 2008 |
| Oddyns Holdings Ltd | Construction | 2019 |