| Muiraspeed Properties Limited | Real estate | 1976 |
| Mukasa James Limited | Other services | 2019 |
| Munro Media Ltd | Arts & recreation | 2024 |
| Muritech Ltd | Information & communication | 2019 |
| Music Talents Limited | Wholesale & retail | 2006 |
| My Local Bobby (2021) Limited | Financial services | 2021 |
| My Local Bobby (2023) Ltd | Other services | 2023 |
| My Local Bobby Limited | Administrative & support | 2016 |
| My Local Bobby Security Products Ltd | Other services | 2023 |
| My Wild Gene Ltd | Wholesale & retail | 2022 |
| Mychippy.Com Limited | Hospitality | 2014 |
| Mycookglobal Ltd | Wholesale & retail | 2024 |
| Myriad Wealth Ltd | Financial services | 2017 |
| N & C Consultancy Ltd | Professional & scientific | 2024 |
| N Andreev Limited | Construction | 2008 |
| Nampara Properties Limited | Real estate | 2016 |
| Nathan Clarke Limited | Arts & recreation | 2017 |
| Nathan Hill Studio Ltd | Other services | 2024 |
| Nature Mate Ltd | Wholesale & retail | 2021 |
| Navarino Grove Limited | Construction | 2020 |
| Naz&Build Limited | Construction | 2018 |
| Neck Ltd | Construction | 2019 |
| Neema's OT Limited | Health & social care | 2016 |
| Nema Home Care Limited | Administrative & support | 2016 |
| Neolink Limited | Financial services | 2022 |
| NEP86 Ltd | Transport & logistics | 2026 |
| New Black Media Partners Limited | Households | 2002 |
| New Forest Paving Group Ltd | Administrative & support | 2025 |
| New Hope Properties Limited | Real estate | 2023 |
| New Model Music Ltd | Arts & recreation | 2024 |
| New Moon Investments Limited | Transport & logistics | 2006 |
| New Pastures Projects Limited | Financial services | 2024 |
| New Resident Productions Limited | Information & communication | 2023 |
| Newham Community Leisure Limited | Arts & recreation | 1992 |
| Newlook Bespoke Upholstery Ltd | Manufacturing | 2024 |
| Nexergy Energy Storage Ltd | Professional & scientific | 2025 |
| Nicolaescu Ltd | Construction | 2016 |
| NIK Construction Ltd | Construction | 2024 |
| Nimrod Security Services Ltd | Administrative & support | 2017 |
| Nini Consulting Limited | Professional & scientific | 2018 |
| Nitrogen Services Limited | Other services | 1996 |
| Nitrogen Services Properties Limited | Real estate | 2016 |
| NL Management Services Limited | Real estate | 2022 |
| Nlel Limited | Hospitality | 2016 |
| Nnjj Group Ltd | Transport & logistics | 2026 |
| Noel Barber Systems Ltd | Professional & scientific | 2026 |
| Nordpower Partners Limited | Energy | 2026 |
| North East Residential Limited | Real estate | 2018 |
| Norwalis Ltd | Health & social care | 2023 |
| NOT That Baldwin Ltd | Information & communication | 2025 |
| Novaverde Energy Ltd | Professional & scientific | 2025 |
| Nueva 1 Limited | Real estate | 2022 |
| Nueva Finance Ltd | Financial services | 2019 |
| Nueva Properties Ltd | Real estate | 2016 |
| Number 10/18 Cedar Close Management Limited | Households | 1987 |
| Nutrition by Yasmin Ltd | Health & social care | 2018 |
| NYX VX Ltd | Information & communication | 2020 |
| O'Connell Investments Ltd | Real estate | 2024 |
| Oajn Electrical Ltd | Construction | 2026 |
| Oak Plastering Limited | Construction | 2024 |
| Oakland Solutions Ltd | Information & communication | 2011 |
| Oaklea Woodland Management Company Limited | Households | 1995 |
| Oaks Properties Development Limited | Real estate | 2016 |
| Oakson Mechanical Services Limited | | 1984 |
| OB Lead Limited | Information & communication | 2020 |
| OCN Contracts Limited | Other services | 2023 |
| Oddwave Media and Goods Limited | Professional & scientific | 2026 |
| Odin Acquisitions Limited | Financial services | 2023 |
| OH Interiors Ltd | Professional & scientific | 2026 |
| Old Tiger Stables Ltd | Real estate | 2020 |
| Oliva Apps Ltd | Information & communication | 2019 |
| Olive Branch Home Services Ltd | Administrative & support | 2024 |
| Olive Wings Ltd | Real estate | 2025 |
| Oliver Marie Properties Ltd | Real estate | 2019 |
| Olivia Property Investments Limited | Real estate | 2016 |
| Olyve Ltd | Professional & scientific | 2025 |
| OM Shakthi UK Ltd | Wholesale & retail | 2025 |
| Omavale Limited | Real estate | 1977 |
| Omlec Stone Installation Ltd | Manufacturing | 2024 |
| One Box London Ltd | Other services | 2018 |
| One Station Way Ltd | Wholesale & retail | 2019 |
| Onwards WE Grow Limited | Real estate | 2021 |
| Opera Ice Cream Limited | Wholesale & retail | 2010 |
| Opportunity Works Ltd | Professional & scientific | 2026 |
| Optimisedcontrols Ltd | Administrative & support | 2026 |
| Oracle Accounting Solutions Limited | Professional & scientific | 2009 |
| Orama Capital Limited | Professional & scientific | 2023 |
| Orbit Support Solutions Limited | Information & communication | 2022 |
| ORT(2023) Ltd | Professional & scientific | 2023 |
| Osborne Integrated Services Ltd | Wholesale & retail | 2026 |
| Osca BIO Energy Ltd | Water & waste | 2017 |
| Osns Investments Ltd | Real estate | 2020 |
| Osns Media Limited | Arts & recreation | 2017 |
| Owen Snee Limited | Professional & scientific | 2008 |
| Owlet Ltd | Professional & scientific | 2025 |
| P D Conway Ltd | Professional & scientific | 2023 |
| P London Services Ltd | Transport & logistics | 2019 |
| P.A.R.C Real Estate Ltd | Real estate | 2019 |
| Pablon Tools Limited | Wholesale & retail | 2003 |
| Pacific Realm Ltd | Professional & scientific | 2017 |