| Micro Moose Ltd | Information & communication | 2021 |
| MID Kent Homes 2025 Limited | Real estate | 2025 |
| Midajon Advisory Ltd | Professional & scientific | 2019 |
| Midnight City Customs Limited | Wholesale & retail | 2025 |
| Millers Electrical and Building Services Limited | Administrative & support | 2007 |
| Mimshack LJC Ltd | Professional & scientific | 2015 |
| Minorca Limited | Professional & scientific | 2017 |
| Minshull Place RTM Company Limited | Real estate | 2004 |
| Mint. Design Limited | Professional & scientific | 2015 |
| Mitchell Architecture Studio Limited | Professional & scientific | 2016 |
| Mitrelaw Ltd | Professional & scientific | 2023 |
| MMX Garden and Property Services Ltd | Administrative & support | 2012 |
| MMX Gcms Ltd | Administrative & support | 2009 |
| MOG Holdings Ltd | Financial services | 2025 |
| Molecule Designs Ltd | Professional & scientific | 2022 |
| Molyneux Cabinetry Limited | Construction | 2012 |
| Montgomery Brothers Limited | Manufacturing | 2003 |
| Mortgage & Lifetime Solutions Limited | Financial services | 2003 |
| Motif U.K. Limited | Manufacturing | 2025 |
| Mould Focus Ltd | Administrative & support | 2022 |
| MOVE4SPORT Limited | Arts & recreation | 2020 |
| Mpower Media Limited | Information & communication | 2018 |
| MR TAP Barbers Ltd | Other services | 2025 |
| MR Taper Ltd | Other services | 2021 |
| MS Home Group Ltd | Real estate | 2022 |
| MSSLPH1 Limited | Real estate | 2026 |
| MTC Sales & Marketing Ltd | Other services | 2025 |
| Muddguard Limited | Professional & scientific | 2023 |
| Multi-Agency Professional Support LLP | | 2012 |
| Mumma, MRS & ME Ltd | Information & communication | 2023 |
| MW Construct Limited | Construction | 2009 |
| My Home Project Ltd | Construction | 2025 |
| My Tutor Plus Limited | Education | 2023 |
| Myles Group Services Ltd | Administrative & support | 2022 |
| Mynew Discovery Ltd | Arts & recreation | 2022 |
| Nadejda Designs Limited | Manufacturing | 2022 |
| Nail Life Ltd | Other services | 2024 |
| Nama Cafe and Cake House Ltd | Wholesale & retail | 2020 |
| Nart Electrical Ltd | Construction | 2023 |
| Nattybites Limited | Hospitality | 2024 |
| Nazareth Holiday Homes Limited | Households | 2021 |
| NCC Refrigeration and Air Conditioning Ltd | Construction | 2021 |
| Ndikasi Consulting Limited | Professional & scientific | 2015 |
| Ness Global Services Limited | Information & communication | 1998 |
| Nevernew Ltd | Manufacturing | 2021 |
| New Dawn Recruitment Agency Limited | Administrative & support | 2012 |
| New Millennium Management Company Ltd | Real estate | 2023 |
| Newall Media Ltd | Other services | 2022 |
| Newblack Events Limited | Administrative & support | 2009 |
| Newnet Express UK Limited | Transport & logistics | 2024 |
| Nightfox Traders Ltd | Wholesale & retail | 2026 |
| Nikskin Ltd | Other services | 2024 |
| Nina Fowler Studio Limited | Arts & recreation | 2014 |
| NL Club Ltd | Real estate | 2026 |
| NM Surveyors Ltd | Professional & scientific | 2025 |
| NO.10 Hairdesign Ltd | Other services | 2003 |
| Noble Cuisine Services Ltd | Hospitality | 2025 |
| Nomadia Limited | Professional & scientific | 2012 |
| Northpoint Holdco Ltd | Financial services | 2023 |
| Northpointe Energy Ltd | Professional & scientific | 2025 |
| Notable.London Limited | Professional & scientific | 2016 |
| Notre Maison Limited | Households | 1997 |
| Nott Brickwork Ltd | Construction | 2009 |
| Nova Homes & Properties Ltd | Real estate | 2026 |
| Nova Sport Advisory Ltd | Professional & scientific | 2026 |
| NOW BE Limited | Professional & scientific | 2026 |
| NR James Ltd | Administrative & support | 2022 |
| NS& a Properties Limited | Real estate | 2024 |
| Nzelu Obgyn Ltd | Health & social care | 2023 |
| O'Reilly Hartfield Limited | Real estate | 2023 |
| Oak Lodge Drive Limited | Households | 1990 |
| Oak Wolf Limited | Financial services | 2020 |
| Oakland Associates Limited | Information & communication | 1993 |
| Oaklands Healthcare Limited | Health & social care | 2025 |
| Oakwood Building Company Limited | Construction | 2017 |
| Odidas Limited | Real estate | 2020 |
| Office 21 Ltd | Information & communication | 2022 |
| Officine Générale UK Limited | Wholesale & retail | 2017 |
| Offline Influence Ltd | Wholesale & retail | 2024 |
| Offsetk Limited | Manufacturing | 2013 |
| Ollie Polly People CIC | Health & social care | 2024 |
| Omega Cafe Ltd | Hospitality | 2022 |
| Omkara Enterprises Ltd | Professional & scientific | 2018 |
| Omni Total Solutions Limited | Manufacturing | 2013 |
| Onenda Ltd | Professional & scientific | 2024 |
| Ongas Ltd | Construction | 2018 |
| Operation Escape Limited | Arts & recreation | 2016 |
| Optimum Info Ltd | Information & communication | 2019 |
| Optimumdc Ltd | Administrative & support | 2026 |
| Or&M Ltd | Professional & scientific | 2011 |
| Orange Octopus Coaching Ltd | Other services | 2020 |
| Orchard Way (South) (Shirley) Limited | Real estate | 1971 |
| Orchard Way(Shirley)(Courts L.M.N.O)Residents Association Limited | Households | 1967 |
| Ordinals Ltd | Information & communication | 2024 |
| Organic Bazaar Ltd | Wholesale & retail | 2021 |
| Orion Prospect Limited | Professional & scientific | 2021 |
| Orpington Express Ltd | Wholesale & retail | 2012 |
| Orpington Kannada Parivaara CIC | Education | 2024 |
| Oshaughnessyretail Ltd | Wholesale & retail | 2025 |
| Osprey Search Ltd | Administrative & support | 2019 |