| Mithport Investments Limited | Real estate | 1962 |
| MM Chilvers Roofing Limited | Construction | 2023 |
| Mmfatik Limited | Information & communication | 2018 |
| Modetower Limited | Professional & scientific | 2000 |
| Modivus Limited | Information & communication | 2025 |
| Mojo Property Management Limited | Real estate | 2024 |
| Montanera Trade & Consulting Ltd | Wholesale & retail | 2020 |
| Monteverde Consulting Limited | Professional & scientific | 2008 |
| Morrell Strategy Ltd | Professional & scientific | 2025 |
| Morse Specialty Limited | Financial services | 2012 |
| Morshead Media Ltd | Information & communication | 2024 |
| Morshead's Old Books Limited | Wholesale & retail | 2008 |
| Morven Residential Limited | Extraterritorial | 2022 |
| Moss Fallon Solicitors Limited | Professional & scientific | 2011 |
| Motoratus Limited | Extraterritorial | 2016 |
| Mountain Top Brickwork Limited | Construction | 2022 |
| MR Taiwan Wiring Co. Ltd | Construction | 2018 |
| MRD GAS Plumbing & Heating Limited | Construction | 2010 |
| MTB Hair Services Ltd | Other services | 2018 |
| MTB Technology Consulting Ltd | Information & communication | 2025 |
| Multi - AGG Limited | Mining & quarrying | 1984 |
| Multilinx Products Ltd | Professional & scientific | 2014 |
| Munro Leasehold Ltd | Real estate | 2025 |
| Munro Property Developments Ltd | Real estate | 2024 |
| Murmuration Systems Ltd | Professional & scientific | 2023 |
| Murray Associates Construction Limited | Construction | 2002 |
| Mustard Seed (Marlborough) Limited | Hospitality | 1992 |
| Mustard Seed Trust (Marlborough) | Wholesale & retail | 1992 |
| My Racing Colours Limited | Manufacturing | 2022 |
| N Marsh Carpentry Services Limited | Manufacturing | 2024 |
| N P Care (Swindon) Ltd | Professional & scientific | 2014 |
| N&R Farming Limited | Agriculture & fishing | 2006 |
| N-Rich Consultants Limited | Administrative & support | 2010 |
| Namtar Advisory Ltd | Professional & scientific | 2026 |
| Nano Electric Bikes Ltd | Manufacturing | 2012 |
| Nant Enterprises Ltd | Professional & scientific | 2014 |
| Nant Y BAI Ltd | Real estate | 2021 |
| Nationwide Storage Solutions Limited | Administrative & support | 2020 |
| Natural Foods Limited | Professional & scientific | 2005 |
| Natural Habitat Landscapes Ltd | Administrative & support | 2018 |
| Natural World Business Projects Limited | Professional & scientific | 1998 |
| Naviga Consulting Limited | Professional & scientific | 2012 |
| Neil Clutterbuck Holdings Limited | Construction | 2024 |
| Neil Clutterbuck Limited | Construction | 2004 |
| Nellgoose Holdings Limited | Professional & scientific | 2023 |
| Neon Grey Limited | Administrative & support | 2016 |
| Netevents International Limited | Administrative & support | 2003 |
| Netvision Consultants Limited | Information & communication | 1999 |
| Neural Forge Ltd | Professional & scientific | 2025 |
| New Energy Farms EU Limited | Agriculture & fishing | 2010 |
| New Media in Business Limited | Information & communication | 1996 |
| Newton's Walk (Baydon) Management Company Limited | Households | 2010 |
| Nexus Wine Collections Limited | Information & communication | 2005 |
| NM Advisors Ltd | Professional & scientific | 2023 |
| NO 1 Beauty Limited | Other services | 2013 |
| Nocton Farms Limited | Extraterritorial | 1964 |
| Nocton Limited | Extraterritorial | 2011 |
| Noodle Guru Ltd | Wholesale & retail | 2014 |
| North House Capital Limited | Financial services | 2026 |
| North to South Ltd | Professional & scientific | 2013 |
| Ntouch Marketing Services Limited | Administrative & support | 2006 |
| Number Forty-One Ltd | Manufacturing | 2025 |
| O T N Plumbing & Heating Limited | Construction | 2014 |
| O'Malley Rail Limited | Professional & scientific | 2013 |
| Oakes House Management Company Limited | Households | 2003 |
| Oakfield Marlborough Ltd | Financial services | 2024 |
| Oakland Capital Management Limited | Financial services | 1981 |
| Oakroom Investment and Property Limited | Financial services | 2016 |
| Ocean Geotechnics Ltd | Professional & scientific | 2018 |
| ODY Brickwork Ltd | Construction | 2023 |
| Ogbourne Construction Services Limited | Construction | 1998 |
| Old Town Hypnotherapy Ltd | Health & social care | 2014 |
| Old Wellonians Limited | Other services | 2025 |
| Oldpowilton Limited | Households | 2010 |
| Olilolli Limited | Professional & scientific | 2018 |
| Omnes Limited | Professional & scientific | 2010 |
| Online Notes Assistant Ltd | Professional & scientific | 2026 |
| Onogo UK Limited | Wholesale & retail | 2021 |
| Openfield Technology Ltd | Information & communication | 2012 |
| Optimum First AID Limited | Health & social care | 2015 |
| Optimumcut Limited | Information & communication | 2014 |
| Orca Sport Limited | Professional & scientific | 1995 |
| Orchard CMC Consulting Ltd | Professional & scientific | 2011 |
| Orestone Advisors Limited | Real estate | 2026 |
| Orion Network Consultants LLP | | 2008 |
| OS Design and Build Ltd | Construction | 2013 |
| Osmond Reporting Limited | Administrative & support | 2012 |
| OUR Eco World Ltd | Extraterritorial | 2006 |
| Outback Self Storage Limited | Real estate | 2022 |
| Outside the Frame Limited | Professional & scientific | 2014 |
| Outstanding Accounts Limited | Professional & scientific | 2025 |
| Overlay Systems Limited | Administrative & support | 2017 |
| Owen Richard Griffiths Ltd | Wholesale & retail | 2024 |
| Oxcampers Ltd | Administrative & support | 2011 |
| Oxfordshire Fencing Group Ltd | Construction | 2021 |
| P J Steel Erection Limited | Construction | 2008 |
| P. DE Jager & Sons Limited | Wholesale & retail | 2008 |
| PAC Farms Limited | Real estate | 1971 |
| PAC Land Limited | Real estate | 2014 |
| Packaging NOT Included Ltd | Wholesale & retail | 2018 |