| Newtec Fabrication Limited | Manufacturing | 2017 |
| Next Level Property Solutions Limited | Administrative & support | 2025 |
| Next Phase Removals Ltd | Transport & logistics | 2025 |
| Nexus Business Networking Ltd | Information & communication | 2024 |
| Nexus Delivery Consultancy Ltd | Professional & scientific | 2024 |
| NF Energy Consultant Limited | Professional & scientific | 2026 |
| Niche Care Homes Limited | Financial services | 2024 |
| Niche Care Properties Limited | Real estate | 2025 |
| Nick Trew and Associates Limited | Professional & scientific | 2020 |
| Nicozy Ltd | Real estate | 2024 |
| Nigel L Johnson Limited | Financial services | 2008 |
| Nigethecat Limited | Professional & scientific | 2022 |
| Nikki Reid Holdings Limited | Financial services | 2026 |
| Ninety Plus Tours Training Ltd | Administrative & support | 2026 |
| Nisomar Ventures Ltd | Other services | 2016 |
| Nixon Architecture Ltd | Professional & scientific | 2021 |
| NM Interiors Ltd | Construction | 2012 |
| NO Bull Mechanics Ltd | Wholesale & retail | 2019 |
| NO Nasties Kids UK Ltd | Wholesale & retail | 2024 |
| No-Vor Limited | Wholesale & retail | 2012 |
| Noble Flooring Ltd | Construction | 2025 |
| Noble Wilson Limited | Real estate | 2001 |
| Nolato PPT Limited | Manufacturing | 2014 |
| Noodle London Partners Limited | Professional & scientific | 2013 |
| Nordic Lodge Management Company Limited | Households | 1991 |
| North Essex Group Ltd | Administrative & support | 2025 |
| North Maldon Growers Limited | Agriculture & fishing | 1964 |
| Norton Brewery Company Limited | Professional & scientific | 2005 |
| Nott GEN Ltd | Professional & scientific | 2026 |
| Nott Invest Ltd | Professional & scientific | 2026 |
| Nova Renewable Energy Ltd | Construction | 2025 |
| NOW Strike Archery Ltd | Manufacturing | 2014 |
| Nowmovin Limited | Real estate | 2016 |
| NP Consulting Group Limited | Professional & scientific | 2025 |
| NPH Groundworks Limited | Extraterritorial | 2016 |
| NU Studios Ltd | Information & communication | 2013 |
| Nual Construction Limited | Transport & logistics | 2025 |
| Nupaf UK Limited | Education | 2026 |
| NX Creative Ltd | Professional & scientific | 2016 |
| OAI Housing Limited | Real estate | 2024 |
| Oak Farm Barns (Management Company) Limited | Construction | 2022 |
| Oak Furniture (Essex) Ltd | Construction | 2010 |
| Oakhill Services Limited | Construction | 2018 |
| OC Logistic Solutions Limited | Transport & logistics | 2024 |
| Ocean Mist Group Ltd | Manufacturing | 2018 |
| Ocean Mist Leith Ltd | Hospitality | 2020 |
| OCF Consulting and Contracting Ltd | Construction | 2026 |
| Ochre CAD Design Ltd | Professional & scientific | 2023 |
| Ocker Engineering Ltd | Construction | 2018 |
| Octane Finance Limited | Extraterritorial | 2018 |
| Octane Ltd | Wholesale & retail | 2018 |
| October Creative Design Ltd | Professional & scientific | 2019 |
| ODG Enterprise Ltd | Wholesale & retail | 2024 |
| Odin Lodge Management Company Limited | Households | 1991 |
| OFF the Shelf Ltd | Professional & scientific | 2025 |
| Office Storage Solutions Ltd | Professional & scientific | 2001 |
| Old Mill Close Management (Maldon) Limited | Real estate | 2007 |
| Oldfield Property Ltd | Construction | 2026 |
| Olivia Hampson Design Limited | Professional & scientific | 2025 |
| Olrose Safety Ltd | Professional & scientific | 2025 |
| OM 1 Construction Ltd | Construction | 2025 |
| OMH Distribution Ltd | Wholesale & retail | 2025 |
| One Reason Limited | Administrative & support | 2022 |
| One SB Limited | Real estate | 2002 |
| One Trafford Edge 100 Limited | Real estate | 2025 |
| One Trafford Edge 44 Limited | Real estate | 2025 |
| One Trafford Edge 52 Limited | Real estate | 2025 |
| One Trafford Edge 92 Limited | Real estate | 2025 |
| Onebit Group Limited | Wholesale & retail | 2017 |
| Online Express Medicines Ltd | Health & social care | 2015 |
| Ooey Gooey Cards Ltd | Wholesale & retail | 2025 |
| Opal Fabrication Limited | Manufacturing | 2004 |
| Opal Laser Ltd | Construction | 2014 |
| Opal Temporary Access Ltd | Administrative & support | 2018 |
| Open Arms Photography Limited | Professional & scientific | 2026 |
| Opies UK Limited | Wholesale & retail | 2006 |
| OPO Maldon Limited | Professional & scientific | 2015 |
| Optical Illusions Limited | Information & communication | 2009 |
| Optihal Ltd | Information & communication | 2024 |
| Orange Peel Media Ltd | Professional & scientific | 2020 |
| Orbital Operations Ltd | Professional & scientific | 2014 |
| Orchid Garden Services Limited | Administrative & support | 2019 |
| Orient Electrical Services Limited | Construction | 2007 |
| Orion Recruitment Solutions Group Ltd | Administrative & support | 2024 |
| Orsett Medical Group Limited | Real estate | 2025 |
| Ortho Solutions Direct Limited | Extraterritorial | 2014 |
| Ortho Solutions Holdings Limited | Financial services | 2012 |
| Ortho Solutions UK Limited | Manufacturing | 2014 |
| Orwell Solutions Limited | Information & communication | 2006 |
| Osea Road Camp Sites Limited | Hospitality | 1955 |
| Osier House Ltd | Households | 2020 |
| OTM Motors Limited | Wholesale & retail | 2024 |
| OTP Network Limited | Arts & recreation | 2023 |
| Otsey Property Limited | Real estate | 2004 |
| Otter Mill Management Company Limited | Households | 2021 |
| Ottley & Sons Groundworks and Demolition Ltd | Construction | 2019 |
| Oxtec Developments Limited | Construction | 2002 |
| Oyster Bookkeeping Ltd | Professional & scientific | 2013 |
| Oyster Smack Properties Limited | Real estate | 2022 |
| P & B Shadwell Ltd | Health & social care | 2012 |