| Mobile Cctv Solutions Limited | Wholesale & retail | 2009 |
| Mojo Electrical Limited | Construction | 2018 |
| Mollart Engineering (Chessington) Limited | Professional & scientific | 2022 |
| Mollart Engineering (Resolven) Limited | Professional & scientific | 2022 |
| Mollart Management Company Limited | Professional & scientific | 2022 |
| Monaco LUX Ltd | Wholesale & retail | 2024 |
| Money Index Ltd | Professional & scientific | 2021 |
| Monjac Distribution Limited | Transport & logistics | 2021 |
| Monogram Capital Limited | Other services | 2009 |
| Montalban Investments Ltd | Hospitality | 2005 |
| Montech Consulting Ltd | Information & communication | 2026 |
| Moorgreen Electrical Maintenance Limited | Construction | 2015 |
| More My Style Ltd | Other services | 2019 |
| Morgan Ellis Football Ltd | Education | 2022 |
| Moriarty Electrical Ltd | Construction | 2024 |
| Mortgage Webb Limited | Financial services | 2004 |
| Moto Historics Ltd | Wholesale & retail | 2012 |
| Motor Options Ltd | Wholesale & retail | 2024 |
| Motus Dynamics Limited | Manufacturing | 2025 |
| Mount Carpentry & Woodworking Ltd | Construction | 2024 |
| Movawall Systems Limited | Construction | 1997 |
| MP Imperial Ltd | Construction | 2019 |
| MP Painter Ltd | Construction | 2016 |
| MP Travel Ltd | Transport & logistics | 2012 |
| MR Construction Consultants Ltd | Construction | 2023 |
| MR Pack UK Ltd | Wholesale & retail | 2026 |
| MR. Bulgogi Ltd | Hospitality | 2011 |
| Mrbss Ltd | Manufacturing | 2022 |
| MRS MC Cakepops Limited | Wholesale & retail | 2026 |
| MSV Services Ltd | Transport & logistics | 2025 |
| Mtap Acquisitions Limited | Real estate | 2025 |
| MTE Tech Consulting Ltd | Information & communication | 2019 |
| Mthl Investment Services Ltd | Financial services | 2011 |
| MTS Paving & Roofing Ltd | Construction | 2021 |
| Much Money (UK) Ltd | Wholesale & retail | 2020 |
| Muddy Paws Grooming Ltd | Wholesale & retail | 2026 |
| Muddy Paws Tolworth Ltd | Other services | 2023 |
| Mughal (Earls Court) Ltd | Hospitality | 2002 |
| Mujo Studio Ltd | Administrative & support | 2023 |
| Mulberry Virginia Water Limited | Real estate | 2019 |
| MYK Art Ltd | Construction | 2023 |
| Mytogs Limited | Other services | 2017 |
| N&S Developments Ltd | Hospitality | 2022 |
| N&S Home Improvements Surrey Ltd | Construction | 2021 |
| Nadarajah Ltd | Real estate | 2022 |
| Nanak OM Ltd | Wholesale & retail | 2023 |
| Nationwide Safety Limited | Construction | 2010 |
| Nature Siam Massage & Spa Ltd | Other services | 2024 |
| Nccnet Limited | Other services | 2025 |
| Neena Properties Ltd | Real estate | 2024 |
| Negna Ltd | Wholesale & retail | 2025 |
| Neoart Construction & Engineering Ltd | Construction | 2026 |
| Neoflux Ltd | Manufacturing | 2025 |
| Netdesignr Ltd | Information & communication | 2016 |
| Netonline Media Limited | Information & communication | 2019 |
| New England Seafood International Limited | Manufacturing | 1990 |
| New Malden Car Services Ltd | Transport & logistics | 2010 |
| New Measures Construction Ltd | Construction | 2025 |
| Newinbeech Limited | Extraterritorial | 1983 |
| Niamh Coffey Limited | Professional & scientific | 2022 |
| Nicholls Residential Limited | Real estate | 2008 |
| Nikola 78 Ltd | Administrative & support | 2023 |
| Nirvana AVA Ltd | Hospitality | 2021 |
| Nivi Software Solutions PVT Ltd | Information & communication | 2017 |
| NKM Studio Ltd | Construction | 2022 |
| NM Heights Limited | Real estate | 2024 |
| NO.1 New Road Residents Company Limited | Households | 2002 |
| NO1 Care 4 YOU Limited | Health & social care | 2023 |
| Noble Build Group Ltd | Construction | 2023 |
| Nonsuch Mortgages Ltd | Financial services | 2026 |
| Northamber PLC | Wholesale & retail | 1980 |
| Norwich EYE Surgery Ltd | Health & social care | 2020 |
| Notably Excellent Ltd | Construction | 2018 |
| Nova 86 Property Limited | Real estate | 2026 |
| Novelec Maintenance Ltd | Other services | 2019 |
| Novelia Investments Limited | Wholesale & retail | 2015 |
| NR Estates Ltd | Construction | 2022 |
| NRG (2012) Limited | Wholesale & retail | 2012 |
| Nu-Afrikka Ltd | Wholesale & retail | 2024 |
| NUC Distribution Limited | Wholesale & retail | 2025 |
| NVP Networks Ltd | Information & communication | 2024 |
| NZR Properties Holdings Ltd | Real estate | 2023 |
| O'Shea Electrical Ltd | Construction | 2024 |
| O. W. Roofing Limited | Construction | 2015 |
| Oak & Stitch Limited | Manufacturing | 2026 |
| Oakcroft Management Limited | Financial services | 2012 |
| Oakmoore Homes Ltd | Construction | 2018 |
| Oakmoore Homes Services Ltd | Construction | 2024 |
| Oakway Consult Ltd | Information & communication | 2015 |
| Obsidian Creative House Ltd | Professional & scientific | 2025 |
| Ocean and Green Art and Culture Support Ltd | Education | 2025 |
| Ocean and Green Consulting Ltd | Wholesale & retail | 2025 |
| Ocean and Green Ltd | Wholesale & retail | 2015 |
| Officehero Management Ltd | Administrative & support | 2019 |
| Ojco Ltd | Wholesale & retail | 2026 |
| Oksan Ltd | Real estate | 2024 |
| Old London Road Property Company Limited | Real estate | 2020 |
| Olerix Ltd | Construction | 2015 |
| Olivan Construction Ltd | Construction | 2024 |
| Oliver Bonas Limited | Wholesale & retail | 1999 |