| Migration USA Limited | Professional & scientific | 2018 |
| Mill Drive and Lane (Crowborough) Limited | Real estate | 1991 |
| Millennium Energy Technologies Limited | Professional & scientific | 2018 |
| Miller International Technical Loss Adjusters Ltd | Financial services | 2015 |
| Minack Mechanical Maintenance Limited | Manufacturing | 1994 |
| Mint Consulting Services Ltd | Professional & scientific | 2022 |
| MJ Cridge (Holdings) Limited | Professional & scientific | 1989 |
| MJW Media Limited | Information & communication | 2008 |
| ML Commercial Properties Limited | Real estate | 2023 |
| MLM UK Holdings Limited | Administrative & support | 2019 |
| MMG (UK) Limited | Professional & scientific | 2013 |
| MMG Accountants Ltd | Professional & scientific | 2013 |
| MMG Publishing US Ltd | Information & communication | 2018 |
| Moby Catering Limited | Hospitality | 2015 |
| Model Beata Limited | Other services | 2024 |
| Moden Group Ltd | Real estate | 2025 |
| MODULAR105 Limited | Construction | 2010 |
| Modus Engine Services Limited | Administrative & support | 2005 |
| Moneywise Financial (Brighton) Ltd | Financial services | 2010 |
| Monson Engineering Limited | Professional & scientific | 1992 |
| Monson Engineering Services Limited | Professional & scientific | 2026 |
| Monterrey LLP | | 2008 |
| Montgomery IT Solutions Limited | Information & communication | 2012 |
| Mood Signs Limited | Manufacturing | 2024 |
| More Than Accounting Ltd. | Professional & scientific | 2021 |
| Morris Air Ltd | Professional & scientific | 2026 |
| Mospod Limited | Professional & scientific | 2014 |
| Motoport Limited | Wholesale & retail | 2003 |
| Mott Projects Ltd | Professional & scientific | 2017 |
| Mountain Business 365 Limited | Administrative & support | 2018 |
| Mountbank Developments Ltd | Construction | 2003 |
| Mower Plant Services Limited | Wholesale & retail | 2011 |
| MPM Ventures Ltd | Real estate | 2015 |
| MR & Missive Limited | Wholesale & retail | 2022 |
| MRG Personal Branding Ltd | Professional & scientific | 2019 |
| MRP Consultancy Services Limited | Health & social care | 2002 |
| MRW Commercial Ltd | Construction | 2024 |
| MRW Investments Ltd | Real estate | 2026 |
| Mulberry Development Management Ltd | Households | 2019 |
| Multiscope Designs Ltd | Information & communication | 2003 |
| Multiscope Energy Ltd | Professional & scientific | 2016 |
| Muras KG Ltd | Hospitality | 2025 |
| Murdoch Accounting Limited | Professional & scientific | 2022 |
| Mutlu Family Ltd | Hospitality | 2024 |
| My Lobster Limited | Administrative & support | 2026 |
| Myareawise Ltd | Administrative & support | 2020 |
| Myconsole Ltd | Information & communication | 2015 |
| Myer Construction Limited | Construction | 1989 |
| Mystic Mouse Limited | Information & communication | 2001 |
| N Stabeler Ltd | Administrative & support | 2022 |
| Napier House Limited | Administrative & support | 1999 |
| Naráic Físeán Limited | Professional & scientific | 2025 |
| NAS Financial Planning Limited | Professional & scientific | 2024 |
| Natilia Collective Ltd | Wholesale & retail | 2026 |
| Natural Facts Limited | Information & communication | 2010 |
| Natural Rediscovery Ltd | Information & communication | 2024 |
| Naturally Pets Limited | Professional & scientific | 2003 |
| Nature North UK Limited | Financial services | 2021 |
| Nature Plus Services Ltd | Professional & scientific | 2024 |
| Nature South UK Ltd | Wholesale & retail | 2020 |
| Naylor Accountancy Group Limited | Professional & scientific | 2024 |
| Nbhn Ltd | Financial services | 2024 |
| Nccad Limited | Administrative & support | 2010 |
| Nectarios Kouvarakis Limited | Health & social care | 2012 |
| NEI Global Relocation Ltd | Administrative & support | 2025 |
| Nestwood Limited | Real estate | 2021 |
| New Milton Heights Ltd | Construction | 2021 |
| New Moonshot Limited | Wholesale & retail | 2018 |
| Newline Recruitment Limited | Extraterritorial | 2014 |
| Newlook Driveways SE Ltd | Construction | 2012 |
| Newman Business Machines & Supplies Limited | Professional & scientific | 1998 |
| Newman Business Machines (Worthing) Limited | Professional & scientific | 1984 |
| Newman Business Solutions Limited | Wholesale & retail | 1980 |
| Newman Computers Limited | Professional & scientific | 1983 |
| Newnham Park Limited | Agriculture & fishing | 1998 |
| Newton Lang Childcare Limited | Health & social care | 2011 |
| Nexus Spa Limited | Other services | 2025 |
| NG Moss Services Ltd | Professional & scientific | 2013 |
| Nicholas IDE Planning and Development Limited | Professional & scientific | 2014 |
| Nick Hope Ltd | Information & communication | 2017 |
| Nicola Keegan Medical Limited | Health & social care | 2022 |
| Nicole Stewart Golf Ltd | Education | 2023 |
| Nikio Ltd | Real estate | 2015 |
| Nineteenth Hole Brewing Limited | Manufacturing | 2022 |
| Noble and Whyte Ltd | Professional & scientific | 2017 |
| Northside Residents' Association Limited | Households | 1971 |
| Nova Cycle Ltd | Information & communication | 2026 |
| Novamo Ltd | Information & communication | 2025 |
| NSE (SE) Ltd | Construction | 2025 |
| Numis Limited | Professional & scientific | 2003 |
| Nutley Sports & Prestige Centre Limited | Wholesale & retail | 2002 |
| NV and AV Limited | Real estate | 2026 |
| NW8-MUMS Ltd | Information & communication | 2021 |
| Nymrod Comms Ltd | Wholesale & retail | 2024 |
| O a J Catering Limited | Hospitality | 2018 |
| OAC Build Ltd | Construction | 2025 |
| OAC Engineering Limited | Construction | 2024 |
| OAC Group Limited | Professional & scientific | 2019 |
| OAC Services Limited | Professional & scientific | 2019 |
| Oak Lodge Park Ltd | Real estate | 2011 |