| Math Salamanders Limited | Administrative & support | 2010 |
| Mayday Technical Services Limited | Administrative & support | 1990 |
| Mayes, Kennedy & Company Limited | Information & communication | 2011 |
| MB Shoe Repairs Limited | Wholesale & retail | 2018 |
| Mcallister's Plumbing and Drains Ltd | Construction | 2024 |
| MCB Spark Ltd | Wholesale & retail | 2025 |
| MCD Training Limited | Transport & logistics | 2017 |
| Mcgillycuddy Ltd | Extraterritorial | 2007 |
| Mcgregor Griston Developments Limited | Construction | 2018 |
| Meadow Hall Veterinary Practice Limited | Professional & scientific | 2017 |
| Meadowlands Estate Limited | Real estate | 2016 |
| Mechsol Ltd | Manufacturing | 2022 |
| Medcom UK Ltd | Wholesale & retail | 2018 |
| Medina Villas Holdings Limited | Real estate | 2025 |
| Medina Villas Management Limited | Real estate | 2025 |
| Melissa Holdings Limited | Financial services | 2021 |
| Melissa Investments Limited | Real estate | 2021 |
| Merryhaven Limited | Real estate | 2019 |
| Merryhill Residents Association Limited | Households | 1990 |
| Merville Galleries Limited | Wholesale & retail | 2003 |
| Meynell Family Properties Limited(The) | Real estate | 1960 |
| Meyrick & Co. Property Limited | Households | 2025 |
| MGH Engineering Ltd | Construction | 2024 |
| Mibri Ltd | Construction | 2014 |
| Michael Jones (Holdings) Limited | Professional & scientific | 2007 |
| Midhurst Aviation Limited | Professional & scientific | 2009 |
| Milanspar Limited | Financial services | 1982 |
| Mill Road Courtyard Limited | Real estate | 2024 |
| Millfold Forestry Ltd | Agriculture & fishing | 2018 |
| Millpepper Limited | Real estate | 2016 |
| Mind Agentic Ltd | Information & communication | 2024 |
| Mini Labs 3D Ltd | Manufacturing | 2024 |
| Miss MOP Limited | Households | 2009 |
| Mission Stories Ltd | Professional & scientific | 2023 |
| MJ Car Hire Limited | Transport & logistics | 2007 |
| Mjpd Aviation Consultants Limited | Education | 2021 |
| MM Legal Eagle Limited | Professional & scientific | 2020 |
| MME Investments Limited | Real estate | 2021 |
| MN Mobile Valeting Ltd | Administrative & support | 2025 |
| Mnm's Ventures Ltd | Real estate | 2024 |
| Mobolajee UK Limited | Administrative & support | 2015 |
| Mode Rigging (UK) Limited | Information & communication | 2026 |
| Monkmead (Storrington) Limited | Extraterritorial | 1969 |
| Monkmead Consulting Ltd | Education | 2015 |
| Monkmead Limited | Extraterritorial | 1962 |
| Mortgage Saving Experts Limited | Financial services | 2016 |
| Move Lettings Ltd | Real estate | 2019 |
| MPS Home Improvements Ltd | Manufacturing | 2018 |
| MPT Partners Ltd | Real estate | 2024 |
| Mrc.Ai Limited | Information & communication | 2026 |
| Murmuration Firm Ltd | Professional & scientific | 2026 |
| MW Electrical (Sussex) Ltd | Construction | 2022 |
| MWS Consulting Ltd | Professional & scientific | 2024 |
| My HR People Ltd | Administrative & support | 2025 |
| My Planning Reports Ltd | Professional & scientific | 2025 |
| Nacarat South Technologies Ltd | Information & communication | 2022 |
| Napper Electrical Ltd | Construction | 2022 |
| NC Moore Properties Limited | Real estate | 2015 |
| Neil Cumming Builders Limited | Construction | 2001 |
| Networks Centre Holding Company Limited | Financial services | 2019 |
| Networks Centre Investments Limited | Extraterritorial | 2021 |
| New Town Green Limited | Real estate | 2024 |
| Nimrod Services (Electronics) Limited | Manufacturing | 1976 |
| Ninety Ventures Ltd | Professional & scientific | 2015 |
| NJC Marketing Limited | Professional & scientific | 2024 |
| NKC Construction Limited | Construction | 2023 |
| NKR Property Investments 2L Ltd | Real estate | 2021 |
| NKR Property Investments Ltd | Real estate | 2017 |
| Nksk Properties Ltd | Real estate | 2024 |
| NML South East Limited | Construction | 2012 |
| Noel O'Connor Medical Repatriation Limited | Health & social care | 2018 |
| Noic Ltd | Arts & recreation | 2025 |
| North Common Freeholders Limited | Administrative & support | 1997 |
| North Oaks Property Management Company Limited | Households | 1996 |
| North Park Sporting Club | Arts & recreation | 2017 |
| Northwind Solutions Limited | Professional & scientific | 2005 |
| Norton Ridge Ltd | Other services | 2024 |
| Novahall Limited | Financial services | 2025 |
| Novio Limited | Professional & scientific | 1998 |
| NS Estates (Southern) Limited | Real estate | 1997 |
| Nsjz Properties Limited | Real estate | 2017 |
| Nuanced Branding Ltd | Professional & scientific | 2024 |
| Nutbourne Vineyards Limited | Manufacturing | 2005 |
| Nyetimber Stables Ltd | Arts & recreation | 2025 |
| Oak END Builders Ltd | Construction | 2026 |
| Oakhurst Guardian Limited | Education | 2009 |
| Oakwood Forest Events Ltd | Other services | 2020 |
| Obex Security Ltd | Administrative & support | 2024 |
| Ocean Club Holidays Limited | Administrative & support | 1992 |
| Ocean Developments Limited | Construction | 1991 |
| OCHESTRA8E Ltd | Professional & scientific | 2023 |
| OFF2PADEL Yorkshire Limited | Arts & recreation | 2025 |
| Offhand Clothing Ltd | Wholesale & retail | 2023 |
| Office Entertainments Ltd | Hospitality | 2018 |
| Offshore Cruising Club Limited | Arts & recreation | 2021 |
| OJ Motors Ltd | Wholesale & retail | 2012 |
| Okomi Limited | Professional & scientific | 2000 |
| Old Barn Books Ltd | Information & communication | 2014 |
| Oliver Hamson Cars Limited | Wholesale & retail | 2019 |
| Oliver Hamson Classics Limited | Transport & logistics | 2023 |