| Monmouthshire Incorporated Law Society(The) | Professional & scientific | 1888 |
| MOO Marketing Ltd | Professional & scientific | 2024 |
| Morestead Cranes Ltd | Wholesale & retail | 2025 |
| Morris Hill Ltd | Wholesale & retail | 2025 |
| Mortgage Complete Ltd | Financial services | 2008 |
| Motahome Ltd | Manufacturing | 2017 |
| Motion Air Limited | Information & communication | 2013 |
| Motion Rail Limited | Information & communication | 2009 |
| Motion Reality Ltd | Professional & scientific | 2018 |
| Motolink South Wales Ltd | Wholesale & retail | 2021 |
| Movebase Ltd | Transport & logistics | 2026 |
| MPS & Co. Developments Ltd | Construction | 2017 |
| MS Applications Ltd | Information & communication | 2023 |
| MSM Partitioning Limited | Construction | 2006 |
| MTP Cara Investments Limited | Real estate | 2025 |
| Mtziongifts Ltd | Wholesale & retail | 2023 |
| Munday Interiors Ltd | Construction | 2023 |
| Munday Property Holdings Ltd | Real estate | 2025 |
| Munpri Properties Limited | Construction | 2025 |
| Mwch Limited | Hospitality | 2026 |
| MWP Trading Limited | Administrative & support | 2018 |
| MWR Accountancy Limited | Professional & scientific | 2011 |
| My Care My Home Limited | Health & social care | 2011 |
| My Respite Care Ltd | Information & communication | 2013 |
| MYA Housing Ltd | Real estate | 2019 |
| N and C Real Estate Ltd | Real estate | 2024 |
| N S James Limited | Wholesale & retail | 2009 |
| N&R Accountancy Ltd | Professional & scientific | 2009 |
| NAC Fleet Consultants Ltd | Transport & logistics | 2017 |
| Nansen Wards Ltd | Wholesale & retail | 2025 |
| Nathan Smiles Limited | Health & social care | 2021 |
| Nationwide Waste Solutions Limited | Water & waste | 2013 |
| Naturscapes Ltd | Administrative & support | 2025 |
| Navelli Ltd | Hospitality | 2025 |
| Nawoc Ltd | Construction | 2025 |
| NCR Renovations Ltd | Construction | 2023 |
| NCS for Spotless Windows Limited | Administrative & support | 2007 |
| NDS Metering Ltd | Construction | 2005 |
| Neil Richards Painting and Decorating Limited | Construction | 2003 |
| Nelson Adelade Ltd | Wholesale & retail | 2025 |
| Nelson Cawte Ltd | Wholesale & retail | 2025 |
| Neocles Limited | Real estate | 2004 |
| Neptune's Daughter Ltd | Professional & scientific | 2018 |
| New Choice Ltd | Hospitality | 2025 |
| New Inn Community Hall | Arts & recreation | 2011 |
| New Inn Community Sports Club Ltd | Arts & recreation | 2025 |
| New Inn Gearbox Centre Limited | Wholesale & retail | 2023 |
| New Inn MOT Centre Limited | Wholesale & retail | 2014 |
| New Millennium Properties Limited | Administrative & support | 2001 |
| New Road Autos Ltd | Wholesale & retail | 2019 |
| New Ross (Holdings) Limited | Financial services | 2019 |
| New Stables Ltd | Wholesale & retail | 2024 |
| New Start Recycling CIC | Water & waste | 2025 |
| Newlands Janson Ltd | Wholesale & retail | 2025 |
| Newman Sydney Ltd | Wholesale & retail | 2025 |
| Newton Building Company Limited | Wholesale & retail | 1935 |
| Nexserve Limited | Information & communication | 2009 |
| Next Risk Solutions Limited | Financial services | 2013 |
| Next Venture Trading Limited | Information & communication | 2012 |
| Nextplay Coaching Ltd | Education | 2026 |
| Ngage Contracting Limited | Administrative & support | 2016 |
| Ngage Group Limited | Administrative & support | 2016 |
| Ngage Rail Limited | Transport & logistics | 2015 |
| Nigel Malts Ltd | Wholesale & retail | 2025 |
| NJS Rail Ltd | Construction | 2019 |
| NO21 Aesthetics Ltd | Other services | 2026 |
| Nooer Ltd | Hospitality | 2018 |
| Norman Kilns Ltd | Wholesale & retail | 2025 |
| Northern Corts Ltd | Wholesale & retail | 2025 |
| Nuclear Ductwork Systems Limited | Extraterritorial | 2012 |
| Nuclear Manufacturing Projects Limited | Extraterritorial | 2011 |
| Nuclear Manufacturing Services Limited | Extraterritorial | 2011 |
| Nuclear Ventilation Projects Limited | Extraterritorial | 2011 |
| Nuclear Ventilation Systems Limited | Extraterritorial | 2012 |
| Nurture Cymru Gofal Ltd | Health & social care | 2016 |
| Nurture Gofal CIC | Health & social care | 2026 |
| Nurture Group Ltd | Construction | 2025 |
| Nurturing Roots Day Nursery Limited | Health & social care | 2023 |
| Nutts Performance Classics Ltd | Wholesale & retail | 2017 |
| Oakleigh Property Group Limited | Real estate | 2026 |
| Occultis Caelus Holdings Limited | Financial services | 2026 |
| Ocean Canute Ltd | Wholesale & retail | 2025 |
| Ogmore Vale Stores Ltd | Wholesale & retail | 2025 |
| Olave Spencer Ltd | Wholesale & retail | 2025 |
| Oleron Marine Limited | Administrative & support | 2016 |
| Ollie Mccartney Photography Ltd | Information & communication | 2023 |
| Omer Francis Ltd | Real estate | 2026 |
| One Transformations Ltd | Construction | 2019 |
| Online Architectural Ltd | Professional & scientific | 2014 |
| Onlinecad Project Management Ltd | Construction | 2017 |
| Onsite Civils Ltd | Construction | 2022 |
| Onslow Bulwark Ltd | Wholesale & retail | 2025 |
| Orka Wellbeing Ltd | Administrative & support | 2023 |
| Osborne 2023 Ltd | Hospitality | 2022 |
| Osborne Sefton Ltd | Wholesale & retail | 2025 |
| Osito's the Little Bear Ltd | Hospitality | 2025 |
| Ostman Sigurd Ltd | Wholesale & retail | 2024 |
| Otto Home Solutions Limited | Real estate | 2025 |
| OUR Little Sphere Ltd | Information & communication | 2014 |
| OUR Motorhomes Limited | Wholesale & retail | 2015 |