| Muruppel Ltd | Health & social care | 2015 |
| Musketeer Motorsport Ltd | Wholesale & retail | 2024 |
| Mustang Star Limited | Administrative & support | 2014 |
| Muster Court Limited | Households | 2000 |
| My Cultur-Ed Ltd | Professional & scientific | 2024 |
| My Tech Team Ltd | Construction | 2021 |
| Mystove Ltd | Wholesale & retail | 2014 |
| Mytradewebsite Ltd | Information & communication | 2025 |
| N Direct Ltd | Construction | 2019 |
| N H Maintenance Ltd | Administrative & support | 2013 |
| Nacass Ltd | Professional & scientific | 2017 |
| Naliot Limited | Professional & scientific | 2022 |
| Nash Films Ltd | Information & communication | 2024 |
| Nash Homes and Property Limited | Hospitality | 2012 |
| Nash Productions Limited | Information & communication | 2019 |
| Nastyhq Ltd | Wholesale & retail | 2021 |
| Navel Enterprises Limited | Arts & recreation | 2012 |
| NBK Trading Ltd | Wholesale & retail | 2024 |
| Ncryption PLC | Professional & scientific | 1996 |
| Nebula IT Systems Ltd | Information & communication | 2022 |
| Neil R Parker Ltd | Construction | 2015 |
| Nelly Smith Limited | Construction | 2025 |
| Nero Waterproofing Consultants Ltd | Construction | 2015 |
| Network City Limits Ltd | Professional & scientific | 2025 |
| Network Technology Limited | Professional & scientific | 1995 |
| Nevo-Star Limited | Health & social care | 2023 |
| New ERA Support Services Limited | Administrative & support | 2025 |
| New Horizon Investments Ltd | Information & communication | 1998 |
| New Horizon Plumbing & Heating Limited | Construction | 2011 |
| New TIM LEY Limited | Hospitality | 2018 |
| New Way Labs Ltd | Information & communication | 2025 |
| Newman Thomson (Holdings) Ltd | Financial services | 2017 |
| Newman Thomson Limited | Manufacturing | 1976 |
| Newturn Eco Solutions Ltd | Construction | 2020 |
| Next Level Games Limited | Information & communication | 2025 |
| Nextus Limited | Manufacturing | 1996 |
| Neyo Dental Specialists Limited | Health & social care | 2022 |
| Neyo Labs Limited | Real estate | 2016 |
| NH Brickwork Ltd | Construction | 2015 |
| NHM Group Holdings Ltd | Financial services | 2022 |
| NIC Connolly Limited | Extraterritorial | 2008 |
| Nicabbi Limited | Administrative & support | 2008 |
| Nicknita Hair Beauty Ltd | Other services | 2025 |
| Nicoletta Mani Limited | Information & communication | 2017 |
| Nicostaffing Ltd | Health & social care | 2019 |
| Nido Psychiatry Limited | Health & social care | 2022 |
| Nine Acres Business Support Ltd | Professional & scientific | 2025 |
| Nine Signals Ltd | Information & communication | 2026 |
| Ninmah Limited | Administrative & support | 2015 |
| Nixon Creative Designs Ltd | Information & communication | 2015 |
| NJD Quality Services Ltd | Professional & scientific | 2018 |
| NJP Property Maintenance Ltd | Construction | 2023 |
| Noble House Letting Ltd | Real estate | 2025 |
| Nook and Notion Ltd | Professional & scientific | 2026 |
| Nord-Plan Limited | Extraterritorial | 2010 |
| North American Vacation Homes (International) Limited | Administrative & support | 2000 |
| North Pole Prosperity Ltd | Real estate | 2024 |
| Nostalgia Construction Group Ltd | Construction | 2026 |
| NOT YET Unicorns Ltd | Administrative & support | 2026 |
| Novorum Group Ltd | Other services | 2025 |
| NOW We'Re Monsters Touring Limited | Arts & recreation | 2012 |
| Nyewood Healthcare Limited | Wholesale & retail | 1995 |
| O Howard Developments Ltd | Construction | 2022 |
| OA PM Ltd | Real estate | 2015 |
| Oak Grange (Folders Lane) Management Company Ltd. | Households | 2016 |
| Oakdene Property Ltd | Real estate | 2025 |
| Oakfields (Plumpton) Management Company Ltd | Households | 2021 |
| Oakland Services (UK) Limited | Health & social care | 2018 |
| Oakleigh Property Consultancy Limited | Administrative & support | 2020 |
| Oakley Accounting Ltd | Professional & scientific | 2006 |
| Oaks Ground Maintenance Ltd | Administrative & support | 2024 |
| OB Fencing Limited | Construction | 2016 |
| Obsessed With Cars Ltd | Wholesale & retail | 2020 |
| Ocean Coaches Limited | Transport & logistics | 2017 |
| Ocean Occupational Health Limited | Health & social care | 2012 |
| Ockley Grange Management Company Limited | Real estate | 2014 |
| Octacube Ltd | Professional & scientific | 2025 |
| Odiham Place M.C. Limited | Real estate | 1995 |
| Offterm Limited | Extraterritorial | 1992 |
| OH My TAN Ltd | Other services | 2025 |
| Oktay Renovations Ltd | Construction | 2023 |
| Old Hellfire Games Ltd | Manufacturing | 2019 |
| Old School Court (Lindfield) Management Company Limited | Households | 2002 |
| Old School Metals Ltd | Manufacturing | 2025 |
| Old Wesleyan Chapel Freehold Limited | Construction | 2021 |
| Oldfield Drive (Haywards Heath) Management Company Limited | Households | 2015 |
| Oldland Mews Management Company Limited | Households | 2013 |
| Oldtimer Spares Ltd | Wholesale & retail | 2020 |
| Olibeneli Ltd | Professional & scientific | 2013 |
| Olive Bidco Limited | Professional & scientific | 2014 |
| Oliver Knoop Limited | Information & communication | 2015 |
| Oliver Young Building and Landscaping Ltd | Administrative & support | 2025 |
| Olivia's Hair & Beauty Ltd | Other services | 2017 |
| Ollie&Nic Accessories Limited | Wholesale & retail | 2014 |
| Omega Building Services Ltd. | Construction | 1989 |
| Omotola PR Limited | Administrative & support | 2009 |
| Omstructure Ltd | Construction | 2024 |
| One Action Holdings Limited | Extraterritorial | 2012 |
| One Ayra (GB) Ltd | Hospitality | 2023 |
| ONE2ONE Glass Ltd | Construction | 2022 |