| Noone-Corby Properties Limited Liability Partnership | | 2024 |
| Nora&Adi Invest Ltd | Real estate | 2025 |
| Nordavol Ltd | Professional & scientific | 2020 |
| NORNOM2 Limited | Extraterritorial | 2019 |
| North Cape Consultancy Ltd | Wholesale & retail | 2025 |
| North Tawton Pharmacy Limited | Wholesale & retail | 2023 |
| Northampton Bakeries Limited | Real estate | 1969 |
| Northants & Rutland Open Studios CIC | Administrative & support | 2025 |
| Northants Celebrant Ltd | Other services | 2024 |
| Northants Mobile Tyres Ltd | Wholesale & retail | 2013 |
| Northants Nominees Limited | Administrative & support | 2016 |
| Northants Property Investment Ltd | Real estate | 2024 |
| Northants Rainbow Collective C.I.C. | Professional & scientific | 2025 |
| Northants Squad Ltd | Administrative & support | 2026 |
| Northdale Park Management Company Limited | Households | 2022 |
| Northis Ltd | Information & communication | 2025 |
| Novae House LLP | | 2026 |
| NP Property Group Limited | Extraterritorial | 2024 |
| NPG Perfect Panel Ltd | Wholesale & retail | 2025 |
| NRI KTR Cell UK Limited | Health & social care | 2026 |
| Nscl Consulting Ltd | Construction | 2020 |
| Nsjc Management Limited | Professional & scientific | 2013 |
| Ntwcommerce Ltd | Wholesale & retail | 2025 |
| Nuage Consultancy Limited | Administrative & support | 2013 |
| Nubiacom Ltd | Information & communication | 2013 |
| Nubis 365 Limited | Information & communication | 2013 |
| Nuenta Clarke Talbot Ltd | Manufacturing | 2007 |
| Number 1 Active Ltd | Wholesale & retail | 2024 |
| Number SIX Consultancy Services Ltd | Professional & scientific | 2023 |
| Nutu Auto Deal Limited | Wholesale & retail | 2016 |
| Nwoha Holdings Limited | Health & social care | 2019 |
| NXT Move Limited | Construction | 2026 |
| Nyaa Solutions Ltd | Real estate | 2023 |
| Nyambenda Limited | Construction | 2019 |
| Nyar’Busia Bargains Ltd | Wholesale & retail | 2022 |
| O&S Investment Ltd | Real estate | 2025 |
| O.M Traditional Masonry Ltd | Construction | 2026 |
| Oadby Land Limited | Construction | 2025 |
| Oakey Dokey Childcare Ltd | Health & social care | 2011 |
| Oakfields Landscaping Ltd | Administrative & support | 2026 |
| Oakham Engineering Limited | Manufacturing | 2006 |
| Oakham Property Investments Limited | Real estate | 2020 |
| Oakley Engineering Ltd | Professional & scientific | 2024 |
| Oakley Framing Limited | Manufacturing | 2008 |
| Oakley Grooming Ltd | Other services | 2021 |
| Oakley Industrial Services Ltd | Administrative & support | 2009 |
| Oakley Leasing Ltd | Administrative & support | 2013 |
| Oakley Vale Community Centre | Other services | 2012 |
| Oakleyfields Care Limited | Health & social care | 2019 |
| Oanna Aesthetics Ltd | Health & social care | 2019 |
| Ocean Fish MD Limited | Wholesale & retail | 2025 |
| Octagon Creative Limited | Administrative & support | 2012 |
| Octrac Consulting Ltd | Professional & scientific | 2018 |
| Odyra Ltd | Real estate | 2025 |
| Odyssey VR Ltd | Information & communication | 2023 |
| OFF Maintenance Ltd | Administrative & support | 2025 |
| OFF the Avenue Properties Ltd | Households | 2026 |
| Office Space Cleaning Ltd | Administrative & support | 2015 |
| Office Space in Town Limited | Real estate | 2008 |
| OG Consulting LLP | | 2017 |
| Ogilvy Natural Ltd | Wholesale & retail | 2017 |
| Okey Dokey Limited | Professional & scientific | 2014 |
| Olah Trans Ltd | Transport & logistics | 2022 |
| Old Garden Place Management Company Ltd | Households | 2026 |
| Oleon Properties H+ Ltd | Real estate | 2024 |
| Oleon Properties Ltd | Real estate | 2021 |
| OLI Investment Solutions Ltd | Transport & logistics | 2023 |
| Olisco Limited | Information & communication | 2014 |
| Olive & Co. Hair Studio Ltd | Other services | 2025 |
| OMH Events Limited | Arts & recreation | 2025 |
| Omnichannel Solutions Limited | Other services | 2014 |
| Omsons Assets Management Ltd | Real estate | 2022 |
| ON Time Trade Ltd | Transport & logistics | 2018 |
| One Group Telecom Holdings Limited | Information & communication | 2014 |
| One Smart Medical Limited | Other services | 2012 |
| One Stop Leaflet Drop Ltd | Professional & scientific | 2024 |
| One Ways Transport Limited | Transport & logistics | 2023 |
| ONE2E-VOLVE Ltd | Information & communication | 2015 |
| Oneills Cafe Limited | Manufacturing | 2021 |
| Oneills Meals Limited | Hospitality | 2025 |
| Onexo Transport Ltd | Transport & logistics | 2026 |
| Only Automotive Limited | Administrative & support | 2024 |
| ONM Energy Limited | Professional & scientific | 2017 |
| Ontap Medical Limited | Health & social care | 2012 |
| Ontex Healthcare UK Limited | Administrative & support | 1988 |
| Onur Decoration Limited | Construction | 2020 |
| Onyx Enhancements Ltd | Other services | 2024 |
| Ophir Limited | Health & social care | 2016 |
| Opthire Ltd | Administrative & support | 2025 |
| Optimum Asbestos Solutions Limited | Professional & scientific | 2013 |
| Optimus Locksmiths Ltd | Administrative & support | 2025 |
| Optimus Pro Ltd | Wholesale & retail | 2026 |
| Oran Building Management Services Limited | Construction | 2022 |
| Orangepack Ltd | Wholesale & retail | 2015 |
| Orchard Board Limited | Real estate | 2006 |
| Orchid Care & Recruitment Ltd | Health & social care | 2023 |
| Orchid Data Systems Limited | Information & communication | 1985 |
| Orchird Health Ltd | Health & social care | 2025 |
| Originsx Ltd | Information & communication | 2026 |
| Orison Healthcare Ltd | Health & social care | 2019 |