| NRT London Limited | Professional & scientific | 2023 |
| NRT Ltd | Transport & logistics | 2010 |
| Ntr-Hr Limited | Administrative & support | 2025 |
| Nu-Plan Builders Ltd | Construction | 2020 |
| Nuke Ltd | Extraterritorial | 2020 |
| Nunn Tech Ltd | Information & communication | 2024 |
| NWG Trustees Limited | Professional & scientific | 2026 |
| NY Ltd | Extraterritorial | 2009 |
| O'Rourke Racing Ltd | Arts & recreation | 2022 |
| Oakfields (Newmarket) Management Company Limited | Real estate | 2020 |
| Oakfields Newmarket Residents Management Company Limited | Households | 2026 |
| Oakland Property Maintenance Limited | Construction | 2014 |
| OAS Handyman CON Ltd | Construction | 2024 |
| Oasis Lifestyle UK Limited | Administrative & support | 2014 |
| Oath Healthcare Suffolk Ltd | Health & social care | 2024 |
| OB Ltd | Extraterritorial | 2009 |
| Ocala Limited | Professional & scientific | 2023 |
| October Ltd | Extraterritorial | 2023 |
| ODH Media Limited | Wholesale & retail | 2026 |
| Odin Informatics Limited | Information & communication | 2020 |
| Oesfx Limited | Wholesale & retail | 2021 |
| OF Ltd | Extraterritorial | 2020 |
| OH SO Brew Ltd | Hospitality | 2025 |
| OIL Tank Change Limited | Construction | 2009 |
| OL Limited | Extraterritorial | 2007 |
| Old Bond Consultants Limited | Administrative & support | 2010 |
| Old Buckenham Stud Limited | Agriculture & fishing | 1994 |
| Old Orchard Developments Limited | Construction | 2004 |
| Oliver ST Lawrence Bloodstock Ltd | Professional & scientific | 2010 |
| Omajoka and Sons Ltd | Health & social care | 2021 |
| Omnihorse Ltd | Arts & recreation | 2022 |
| Omnihorse Racing Ltd | Arts & recreation | 2022 |
| ON Ltd | Extraterritorial | 2020 |
| ON the PEG Pursuits Ltd | Wholesale & retail | 2023 |
| One Eyed Meow Limited | Wholesale & retail | 2023 |
| Onedayone Fruit UK Ltd | Wholesale & retail | 2025 |
| Open 7 Curry Ltd | Hospitality | 2025 |
| Operational Insights Limited | Professional & scientific | 2025 |
| Optical Fiber Packaging Ltd | Manufacturing | 2015 |
| Optimal Health Strategies Limited | Health & social care | 2024 |
| Optimum Performance Academy Ltd | Other services | 2025 |
| Optimum Performance Consultancy Ltd | Health & social care | 2026 |
| Optimum Performance Ltd | Health & social care | 2026 |
| Opulence Bloodstock Limited | Arts & recreation | 2024 |
| Opulence Thoroughbreds Breeding Limited | Agriculture & fishing | 2022 |
| Orange Ltd | Extraterritorial | 2020 |
| Orange Shop 1 Ltd | Wholesale & retail | 2026 |
| Orange Windmill Hospitality Ltd | Hospitality | 2025 |
| Orbis Bloodstock Ltd | Agriculture & fishing | 2023 |
| Orbital Racing Gold Limited | Arts & recreation | 2023 |
| Orbital Racing Group Limited | Arts & recreation | 2021 |
| Orchard Bloodstock Limited | Agriculture & fishing | 2012 |
| Orchard Place Bloodstock Limited | Agriculture & fishing | 2025 |
| Orchid Aromatech Ltd | Agriculture & fishing | 2021 |
| Orographic Lift Limited | Information & communication | 2015 |
| Osborne Equine Services Limited | Professional & scientific | 2015 |
| Osborne Ventures Limited | Financial services | 2024 |
| Oscehub Vets Limited | Information & communication | 2026 |
| OSS Bars Limited | Wholesale & retail | 2023 |
| OSS Events Limited | Wholesale & retail | 2023 |
| OSS Live Limited | Administrative & support | 2019 |
| OT Breeding Limited | Agriculture & fishing | 2023 |
| OT Ltd | Extraterritorial | 2009 |
| OU Ltd | Extraterritorial | 2010 |
| OUR Lady of Walsingham Catholic Multi Academy Trust | Education | 2013 |
| Outside World Limited | Wholesale & retail | 2023 |
| OV Ltd | Extraterritorial | 2024 |
| OW Limited | Extraterritorial | 2015 |
| Oxpark Bloodstock UK Ltd | Agriculture & fishing | 2026 |
| Oxydise Ltd | Administrative & support | 2023 |
| OZ Ltd | Extraterritorial | 2010 |
| Ozzengin Ltd | Other services | 2024 |
| P & M 79 Ltd | Construction | 2017 |
| P Banks Associates Limited | Professional & scientific | 2011 |
| P C Carpentry Services Limited | Construction | 2015 |
| P Collins Plumbing and Heating Limited | Construction | 2026 |
| P. & B. Flooring Limited | Wholesale & retail | 1975 |
| PAD Security Systems Ltd | Administrative & support | 2023 |
| Paint ME Pretty Ltd | Other services | 2020 |
| Palace House Trading Ltd | Wholesale & retail | 2016 |
| Palmer Hospitality Ltd | Hospitality | 2025 |
| Paltridge Estates Construction Ltd | Other services | 1994 |
| Paltridge Estates Limited | Construction | 1990 |
| Paradise (a Land of Fulfilment) Ltd | Other services | 2025 |
| Pareidolia Projects Ltd | Real estate | 2024 |
| Parfree Limited | Professional & scientific | 2000 |
| Park Home Life Holdings Limited | Administrative & support | 2022 |
| Park Home Life Limited | Administrative & support | 1963 |
| Park Lane Restaurants Ltd | Hospitality | 2024 |
| Park Lodge Stables Ltd | Professional & scientific | 2005 |
| Parker Halliday Ltd | Hospitality | 2019 |
| Parkersync Ltd | Information & communication | 2024 |
| Parkstone Limited | Wholesale & retail | 1981 |
| Partacoona Investments Limited | Real estate | 1964 |
| Passion Barber Ltd | Other services | 2023 |
| Paths Worldwide Ltd | Professional & scientific | 2019 |
| Patrick Owens Racing Limited | Arts & recreation | 2016 |
| Patrick Round Consulting Ltd. | Professional & scientific | 2009 |
| Paul Brown Electrician Limited | Manufacturing | 2003 |
| Paul Clarke Racing Limited | Arts & recreation | 2014 |