| North Pro-Mech Ltd | Construction | 2024 |
| North Star Books Ltd | Arts & recreation | 2021 |
| Northamptonshire Carers | Health & social care | 1997 |
| Northamptonshire Cleaning Services Limited | Administrative & support | 2016 |
| Northamptonshire Domestic Abuse Service | Health & social care | 1994 |
| Northamptonshire Golf Ltd | Arts & recreation | 2015 |
| Northamptonshire Physio Clinic Limited | Health & social care | 2019 |
| Northamptonshire Ventures Ltd | Financial services | 2024 |
| Northants Commercial Projects Limited | Professional & scientific | 2025 |
| Northants Community Care Limited | Health & social care | 2014 |
| Northants Delight Limited | Hospitality | 2018 |
| Northants Developments Limited | Construction | 2022 |
| Northants Engineering and Property Refurbishment Ltd | Construction | 2019 |
| Northants Flat Roofing Specialists Ltd | Construction | 2025 |
| Northants Housing Limited | Real estate | 2014 |
| Northants Online Ltd | Information & communication | 2021 |
| Northants Pro Clean Ltd | Administrative & support | 2024 |
| Northants Welding Supplies Limited | Wholesale & retail | 1981 |
| Northantsgrabs Limited | Water & waste | 2024 |
| Northbourne Property Limited | Professional & scientific | 2000 |
| Northedge Packaging Limited | Wholesale & retail | 1988 |
| Northwork Ventures Ltd | Information & communication | 2026 |
| NOT Designer Limited | Wholesale & retail | 2002 |
| Nota Reliance Ltd | Public administration | 2022 |
| NOW Trading Incorporation Ltd | Wholesale & retail | 2019 |
| NP Consultants & Management Services Ltd | Financial services | 2024 |
| NPB Transport Limited | Transport & logistics | 2018 |
| NPR Technology Limited | Information & communication | 2010 |
| NPS (Shoes) Limited | Administrative & support | 2006 |
| NRG UK Group Holdings Ltd | Real estate | 2024 |
| NRG UK Group Limited | Wholesale & retail | 2009 |
| NRG UK Group SPV Ltd | Energy | 2025 |
| NRS Plumbing & Heating Specialist Ltd | Construction | 2018 |
| Nsj-Logistics Ltd | Transport & logistics | 2013 |
| NSL IT Ltd | Information & communication | 2024 |
| NSP Trading Limited | Real estate | 1999 |
| NTD Electrical Ltd | Administrative & support | 2016 |
| Number One Works Limited | Construction | 1998 |
| Nurtureai Ltd | Information & communication | 2025 |
| Nurturing Naturally Limited | Health & social care | 2017 |
| Nutri-Know Limited | Manufacturing | 2025 |
| Nuvaulttcg Ltd | Wholesale & retail | 2025 |
| NV Finance Limited | Transport & logistics | 2024 |
| NWL Plumbing Ltd | Construction | 2009 |
| NYB Audio Visual Consultancy Ltd | Professional & scientific | 2026 |
| Nyia Health Care Services Ltd | Health & social care | 2023 |
| NYX Property Capital Ltd | Real estate | 2026 |
| Oak & Grain Joinery Limited | Manufacturing | 2025 |
| Oak Grove Renewable Energy Limited | Energy | 2015 |
| Oak House Park Homes Ltd | Other services | 2025 |
| Oak Lane Cleaning Company Ltd | Administrative & support | 2023 |
| Oak Lane Group Limited | Financial services | 2025 |
| Oak Lane Property Investments Ltd | Real estate | 2025 |
| Oakfield (Easton Maudit) Limited | Health & social care | 1981 |
| Oakhaus Ltd | Construction | 2012 |
| Oakley Inns & Taverns Limited | Hospitality | 2024 |
| Oakmore 2022 Ltd | Professional & scientific | 2022 |
| Oakthorn Properties Limited | Real estate | 1995 |
| Oaktree Property Maintenance Limited | Construction | 2009 |
| Obek (U.K.) Limited | Professional & scientific | 1984 |
| Obibini Limited | Health & social care | 2023 |
| Obsidian Health Consulting Ltd | Administrative & support | 2026 |
| Occasions by Rebecca Limited | Manufacturing | 2018 |
| OCM (Hartwell) Ltd | Households | 2011 |
| Octav Audio Visual Ltd | Professional & scientific | 2024 |
| ODD Bulls Ltd | Wholesale & retail | 2018 |
| Odiseo Eyewear Ltd | Wholesale & retail | 2022 |
| OEM Services Ltd | Professional & scientific | 2015 |
| OES Properties Limited | Construction | 2005 |
| Ofertemutare Limited | Information & communication | 2026 |
| OFF the Streets NN CIC | Education | 2021 |
| Office Equipment Servicing Limited | Other services | 2006 |
| Ofomah’S Group Ltd | Health & social care | 2023 |
| OG Gelato Ltd | Manufacturing | 2025 |
| Ogden Research Limited | Professional & scientific | 2016 |
| Ogya Limited | Construction | 2025 |
| OHA Style Ltd | Wholesale & retail | 2025 |
| OK Care C.I.C. | Public administration | 2021 |
| Okae Ultrasound Services Ltd | Health & social care | 2025 |
| Okaser Educators Ltd | Information & communication | 2025 |
| Okavango Safaris Ltd | Extraterritorial | 1988 |
| Okra Indian Grill Restaurant Ltd | Hospitality | 2018 |
| Olars Services Limited | Administrative & support | 2020 |
| Old TE MLA Limited | Real estate | 2025 |
| Old Vicarage Apartments (Management) Limited | Real estate | 2001 |
| Olea London Limited | Wholesale & retail | 2014 |
| Olga Ltd | Transport & logistics | 2015 |
| Olive Tree Property Ltd | Real estate | 2023 |
| Oliver Enzo Lombardi Ltd | Wholesale & retail | 2023 |
| Olomi Holdings Ltd | Financial services | 2023 |
| Oltean Limited | Transport & logistics | 2015 |
| Olti Ltd | Construction | 2022 |
| Olton Property Services Ltd | Construction | 2026 |
| OM Physiotherapy by Vikas Ltd | Health & social care | 2026 |
| Omindra Limited | Real estate | 2016 |
| Omix Trans Ltd | Transport & logistics | 2025 |
| Ommateum Ltd | Information & communication | 2025 |
| Omnec Ltd | Wholesale & retail | 2019 |
| ON Point Valeting Limited | Other services | 2024 |
| One Build Developments Limited | Construction | 2017 |