| MGP Steel Erection Limited | Construction | 1998 |
| MH Roofing Contractors Limited | Construction | 2006 |
| Michael Robinson Limited | Other services | 2003 |
| Mickstar Limited | | 1987 |
| Mike Hill Architectural Services Limited | Professional & scientific | 2007 |
| Milewall Limited | Extraterritorial | 2007 |
| Mill House Financial Management Limited | Professional & scientific | 1997 |
| Mill House UK Limited | Professional & scientific | 1997 |
| Milton Hall Fields GWT Limited | Agriculture & fishing | 2022 |
| Minerva Management Services Limited | Professional & scientific | 2006 |
| Ministry of Fones Limited | Wholesale & retail | 2003 |
| Mison Services Limited | Real estate | 2004 |
| MJ & JH Walsh Limited | Health & social care | 2002 |
| Mobilytec Limited | Professional & scientific | 2002 |
| Moharib Properties Ltd | Transport & logistics | 2007 |
| Monarch Software Systems Limited | Information & communication | 1990 |
| Mondalco Ltd. | Wholesale & retail | 2015 |
| Money Penny Holdings Limited | Administrative & support | 2006 |
| Moneypenny Eastbourne Limited | Professional & scientific | 2005 |
| Montpelier Crescent Management Limited | Households | 1991 |
| Moorbeech Limited | Real estate | 2006 |
| Morgan Classic Wines Limited | Wholesale & retail | 1999 |
| Morphia Limited | Professional & scientific | 2006 |
| Motcombe Mews (Eastbourne) Limited | Households | 1984 |
| Motors & Mowers Limited | Other services | 2002 |
| Mount Park Holdings Limited | Professional & scientific | 1961 |
| Mountain Activities Limited | Other services | 2002 |
| Mphlighting Limited | Information & communication | 2012 |
| MPI Financial Advice Ltd | Financial services | 2021 |
| MR Beds of Sussex Limited | Wholesale & retail | 2003 |
| MS Solicitors Limited | Professional & scientific | 2004 |
| Much ADO Books Limited | Wholesale & retail | 2003 |
| Muktha Tandoori Limited | Hospitality | 2001 |
| Mulberry Fine Art Limited | Administrative & support | 2002 |
| Multiple Drafts Ltd | Information & communication | 2006 |
| Music First Audio Limited | Manufacturing | 2003 |
| My Productions Limited | Information & communication | 2002 |
| N & G Property Investments Limited | Real estate | 2005 |
| N & M Enterprises Limited | Professional & scientific | 2008 |
| N P Veteran Engineering Limited | Wholesale & retail | 2002 |
| Nails and Ladders Limited | Administrative & support | 2005 |
| Namrick Limited | Wholesale & retail | 1980 |
| Nashopper Investments Limited | Real estate | 2001 |
| Natty Threads Ltd | Manufacturing | 2007 |
| Natural Balance (UK) Limited | Health & social care | 2007 |
| NC Projects Limited | Professional & scientific | 2007 |
| Net-It.Org Limited | Arts & recreation | 2007 |
| Netbase Systems Limited | Administrative & support | 2002 |
| Netpack Services Limited | Real estate | 2000 |
| Network Strategies Limited | Wholesale & retail | 1988 |
| Nevill Court Residents Company Limited | Households | 2003 |
| New Britannia Construction Limited | Extraterritorial | 1997 |
| New Church Road Investments Limited | Real estate | 2002 |
| Newleaf Wakefield Road Limited | Households | 2000 |
| News and Features Limited | Information & communication | 2007 |
| Newtons Property Investments Limited | Real estate | 2005 |
| Next Investment Properties Limited | Real estate | 1999 |
| Nicesprint Limited | Professional & scientific | 1988 |
| Nicosia 23 (Holdings) Ltd | Financial services | 2019 |
| Nido Marketing Limited | Professional & scientific | 2003 |
| Nikwax Limited | Manufacturing | 1995 |
| Nine Albany Villas (Hove) Ltd. | Households | 1993 |
| Nine Clermont Road Limited | Households | 1996 |
| Nine Palmeira Square (Hove) Limited | Households | 1988 |
| Nine to Five (Sussex) Limited | Construction | 1994 |
| Niris Computer Services Limited | Information & communication | 2006 |
| NJA Property Services and Fencing Ltd | Construction | 2021 |
| NMW Accountancy Limited | Professional & scientific | 2017 |
| NO. 4 Westbourne Villas (Management) Limited | Households | 1973 |
| NO. 45 Sillwood Street Brighton Limited | Professional & scientific | 1990 |
| NO.42 Limited | Extraterritorial | 2001 |
| NO.7 Limited | Real estate | 2001 |
| Nolan Networks Limited | Professional & scientific | 2004 |
| Norbury Close (Crowborough) Limited | Real estate | 2001 |
| Norman Wildblood and Co. Limited | Construction | 1974 |
| North West Meats (Suffolk) Limited | Transport & logistics | 1976 |
| Northern Ballet School Limited | Education | 1995 |
| Norton Property Limited | Real estate | 2004 |
| Norvett Electronics Limited | Construction | 1960 |
| Noticross Investments Limited | Financial services | 1964 |
| Nova Mobility Systems (UK) Limited | Extraterritorial | 2006 |
| Novatech Measurements Limited | Manufacturing | 1972 |
| Novidex Limited | Professional & scientific | 2005 |
| Novus Management Limited | Professional & scientific | 2003 |
| NRG Mortgages Limited | Real estate | 2007 |
| NRG Performance Certificates Limited | Other services | 2005 |
| NSP Holdings Limited | Financial services | 2005 |
| NT Holdings Limited | Professional & scientific | 2006 |
| Nu-Glow Cleaning Services Limited | Administrative & support | 1999 |
| Nuvo Dent Limited | Health & social care | 2006 |
| O W M & M Design Limited | Professional & scientific | 1988 |
| O'Neil Software Limited | Information & communication | 1996 |
| Oak & RYE Ltd | Hospitality | 2026 |
| Oakland Vale Limited | Professional & scientific | 2003 |
| Oakley New Homes (East Kent) Limited | Professional & scientific | 2003 |
| Oakley New Homes (South East) Limited | Professional & scientific | 2001 |
| Oakley New Homes (Sussex) Limited | Professional & scientific | 2000 |
| Oakley Real Estate Services Limited | Extraterritorial | 2002 |
| Oasis Windows & Doors Limited | Construction | 2005 |
| OBC the Accountants Limited | Professional & scientific | 2004 |