| Nokes & Co Limited | Professional & scientific | 2009 |
| Nomadik Stretch Tents Limited | Administrative & support | 2016 |
| Nook Maintenance Ltd | Administrative & support | 2024 |
| Nook Property Holdings Ltd | Real estate | 2024 |
| Nora Grill Ltd | Hospitality | 2026 |
| Nordic and Nice Ltd | Wholesale & retail | 2025 |
| Norfolk Tyre Recycling Limited | Other services | 2025 |
| North 1 Cleaning Limited | Administrative & support | 2018 |
| North B Estates Limited | Real estate | 2023 |
| North South Electrical Services (Residential) Ltd | Construction | 2025 |
| North South Electrical Services Ltd | Construction | 2024 |
| North- Coffee and Wine Limited | Hospitality | 2023 |
| Northern Pocket Paradise Ltd | Real estate | 2024 |
| Northville Holdings Limited | Financial services | 2021 |
| Nouvion Limited | Other services | 2018 |
| Nova Therapy London Ltd | Other services | 2016 |
| Novo Hair Limited | Other services | 2000 |
| NOW Marketing Global Limited | Information & communication | 2010 |
| NP Transport Services Ltd | Transport & logistics | 2015 |
| Nplh Studio Ltd | Hospitality | 2025 |
| Npwebservices Ltd | Information & communication | 2009 |
| NQ Energy Solutions Ltd | Households | 2022 |
| NRD (Essex) Ltd | Extraterritorial | 2017 |
| NRE Property Limited | Real estate | 2024 |
| NRM Transport Limited | Transport & logistics | 2025 |
| NTM Electrical Limited | Manufacturing | 2007 |
| Nudev Ltd | Construction | 2023 |
| Number 33 Grand Parade Limited | Real estate | 2022 |
| Number 48 Leigh Park Road (Management) Limited | Administrative & support | 1977 |
| Nume Hair & Beauty Limited | Other services | 2025 |
| Nunn Contracting Ltd | Construction | 2025 |
| Nunn Group Ltd | Financial services | 2017 |
| Nunn Holdings Ltd | Real estate | 2019 |
| Nuren Ltd | Administrative & support | 2020 |
| Nursing ETC Limited | Information & communication | 2022 |
| Nusa Holdings Ltd | Real estate | 2021 |
| Nuworksplumbingheating Ltd | Energy | 2024 |
| NVP Energy UK Limited | Water & waste | 2013 |
| Nwright Consulting Limited | Professional & scientific | 2026 |
| O C Electrical Installations Limited | Construction | 2008 |
| O Picado Ltd | Hospitality | 2010 |
| O S Sports and Social Club | Hospitality | 1988 |
| O'Connor Contracts Ltd | Construction | 2015 |
| O'Shea Carpets Limited | Construction | 1998 |
| O.M Essex Catering Ltd | Hospitality | 2025 |
| Oak Avenue Development Ltd | Construction | 2025 |
| Oak Lodge (Leigh-On-Sea) Residents Association Limited | Households | 1974 |
| Oak Manor Holdings Limited | Administrative & support | 2023 |
| Oak Manor Investments Limited | Administrative & support | 2003 |
| Oak Manor Properties Limited | Administrative & support | 2016 |
| Oakhurst Investments Ltd | Real estate | 2013 |
| Oaklake Carpentry Ltd | Manufacturing | 2016 |
| Oakleigh Wealth Management Limited | Financial services | 2022 |
| Oakrose Limited | Wholesale & retail | 2021 |
| Oakview Property Group Ltd | Real estate | 2024 |
| Oakwold Holdings Limited | Financial services | 2016 |
| Oakwold Homes Limited | Construction | 2011 |
| Oakwold Investments Limited | Construction | 2013 |
| Oakwold Properties Limited | Real estate | 2016 |
| Oakwood Carpentry Ltd | Manufacturing | 2025 |
| Obeau Limited | Real estate | 2025 |
| Obex Properties Ltd | Real estate | 2020 |
| Obua Ltd | Professional & scientific | 2022 |
| Obyr Ltd | Information & communication | 2025 |
| Ocean Crossing Education Limited | Education | 2022 |
| Ocean Residential Ltd | Real estate | 2006 |
| Ocularis Limited | Wholesale & retail | 2010 |
| Odinson-Landscapes Ltd | Administrative & support | 2020 |
| Odyssey Trading & Consultancy Limited | Wholesale & retail | 2022 |
| OF Life & Lemons Limited | Wholesale & retail | 2015 |
| Offcote Investments Limited | Financial services | 2020 |
| Office Gods and Mods Ltd | Wholesale & retail | 2024 |
| Officer Properties Ltd | Real estate | 2021 |
| Offshore Marine Enterprises Limited | Wholesale & retail | 2012 |
| Ofr-Skl Consulting Ltd | Professional & scientific | 2026 |
| Ogen Marine Ltd | Education | 2019 |
| OGK Window & Solar Limited | Administrative & support | 2025 |
| OGK Window & Solar Residential Limited | Administrative & support | 2025 |
| OIE UK Investments Ltd | Real estate | 2025 |
| OJH Property Limited | Real estate | 2023 |
| Okaa Property Limited | Construction | 2019 |
| Olar Developments Ltd | Construction | 2023 |
| Old Foundry Events Ltd | Hospitality | 2024 |
| Old Leigh Garden Co. Ltd | Administrative & support | 2025 |
| Old Leigh Limited | Professional & scientific | 2012 |
| Old Stock Antiques Ltd | Wholesale & retail | 2021 |
| Oliver & Sons Ltd | Manufacturing | 2016 |
| Oliver James Plumbing and Heating Limited | Construction | 2019 |
| Oliver Moss Music Limited | Other services | 2002 |
| Olivermarie Limited | Health & social care | 2012 |
| Olivia Rose Media Limited | Professional & scientific | 2017 |
| Olli Leivers Ltd | Information & communication | 2022 |
| Olliffe Enterprises Limited | Health & social care | 2024 |
| Olympic Plumbing Services Limited | Other services | 2009 |
| Olympus 12 - Cargo Services Ltd | Transport & logistics | 2013 |
| Olympus Capital Group Limited | Financial services | 2026 |
| OM Phoenix Ltd | Professional & scientific | 2018 |
| OM Shiv Limited | Financial services | 2011 |
| OMA Group Holdings Limited | Financial services | 2026 |
| OMA Property Investments Limited | Real estate | 2026 |