| Numberation Ltd | Professional & scientific | 2026 |
| Numero Coffee Limited | Hospitality | 2022 |
| Numerus Ltd | Professional & scientific | 2006 |
| Numifi Solutions Ltd | Administrative & support | 2025 |
| Nuncek Marek 82947 Limited | Transport & logistics | 2014 |
| Nuno Holdings Limited | Financial services | 2026 |
| Nurac Limited | Health & social care | 2021 |
| Nurani Travel and Cargo Ltd | Other services | 2014 |
| Nurob Consulting Limited | Professional & scientific | 2024 |
| Nursery Rhymes Chesterfield Ltd | Health & social care | 2021 |
| Nurses Friend Limited | Administrative & support | 2017 |
| Nurtix Ltd | Health & social care | 2026 |
| Nurture Haven Ltd | Health & social care | 2020 |
| Nurturel Ltd | Other services | 2020 |
| Nurtury (Northants) Limited | Education | 1999 |
| Nutralight Engineering Limited | Professional & scientific | 2022 |
| Nutrition Plus Ltd | Health & social care | 2015 |
| Nuts About Health Limited | Health & social care | 2018 |
| Nutzz Electronic Ltd | Wholesale & retail | 2014 |
| Nuude (Npton) Ltd | Other services | 2018 |
| Nuude Kingsthorpe Limited | Other services | 2024 |
| Nuvasive UK Limited | Professional & scientific | 2005 |
| Nuvos Hospitality Ltd | Hospitality | 2025 |
| Nuvu Windows Limited | Manufacturing | 2005 |
| NV & BN Construction Ltd | Construction | 2021 |
| Nvik Transport Ltd | Transport & logistics | 2025 |
| NVQ Ltd | Education | 2024 |
| Nvrnorthampton Community Interest Company | Education | 2020 |
| NW London Builders Ltd | Construction | 2017 |
| NW Transport Ltd | Transport & logistics | 2025 |
| NW1 Nails Limited | Wholesale & retail | 2014 |
| Nwando Okafor Ltd | Wholesale & retail | 2020 |
| NWC Properties Limited | Real estate | 2023 |
| Nwild Chiro Ltd | Health & social care | 2018 |
| NX Group Limited | Financial services | 2020 |
| NX Logistics Ltd | Transport & logistics | 2011 |
| NXT GEN Enterprises Ltd | Wholesale & retail | 2019 |
| NXT GEN Lift Services Ltd | Construction | 2018 |
| Nxtransport Limited | Transport & logistics | 2010 |
| Nyathi Health Care Limited | Health & social care | 2013 |
| Nyce Service Ltd | Other services | 2025 |
| Nyeafe Consulting Ltd | Health & social care | 2025 |
| NYG Construct Ltd | Construction | 2025 |
| Nygw Limited | Information & communication | 2025 |
| Nyk's Services Ltd | Construction | 2019 |
| NYO2 Ltd | Wholesale & retail | 2013 |
| O & L Couriers Ltd | Transport & logistics | 2014 |
| O Allen Ltd | Financial services | 2017 |
| O M George Limited | Health & social care | 2013 |
| O YES Kebab Ltd | Hospitality | 2019 |
| O&A Haulage UK Ltd | Transport & logistics | 2025 |
| O&C Empress Ltd | Administrative & support | 2025 |
| O&E Food Ltd | Wholesale & retail | 2018 |
| O&M Prestige Mortgage & Protection Ltd | Financial services | 2024 |
| O&O Vital Ltd | Health & social care | 2025 |
| O'Brien Heating Services Limited | Construction | 2018 |
| O'Connor and Co (Financial Services) Limited | Financial services | 2011 |
| O'Connor Projects Ltd. | Information & communication | 2007 |
| O'Hara Edible Oils Ltd | Administrative & support | 2008 |
| O'Hara Waste OIL Limited | Water & waste | 2012 |
| O'Mahoney Hospitality Ltd | Hospitality | 2017 |
| O'Riordan Bond Estate Agents Limited | Real estate | 1997 |
| O'Riordan Bond Financial Services Limited | Financial services | 2012 |
| O'Riordan Bond Holdings Limited | Professional & scientific | 1998 |
| O'Riordan Bond Lettings Limited | Real estate | 2010 |
| O3 Food Stores Ltd | Hospitality | 2023 |
| OA Bean Investments Limited | Real estate | 2021 |
| OAC Images Ltd | Arts & recreation | 2022 |
| Oak ASH Limited | Construction | 2002 |
| Oak Comfort Ltd | Health & social care | 2026 |
| Oak Creek Limited | Professional & scientific | 2020 |
| Oak Homes Development Company Limited | Real estate | 2020 |
| Oak House Traders Ltd | Wholesale & retail | 2026 |
| Oak Housing Developments Limited | Real estate | 2023 |
| Oak Tree Builders Merchants Limited | Wholesale & retail | 2015 |
| Oak Tree Farm - Brixworth Ltd | Agriculture & fishing | 2025 |
| Oak Tree House Ltd | Real estate | 2021 |
| Oak Wood Antiques Ltd | Wholesale & retail | 2018 |
| Oakbridge Investment Holdings Limited | Financial services | 2026 |
| Oakden Limited | Real estate | 1994 |
| Oakdene Roof Solutions Ltd | Construction | 2017 |
| Oaken Properties Limited | Households | 2019 |
| Oakfields Building Limited | Construction | 2005 |
| Oaklands DS Ltd | Health & social care | 2019 |
| Oaklane Homes (Midlands) Limited | Real estate | 2025 |
| Oakleaf Building & Property Services Ltd | Construction | 2014 |
| Oakleaf Vita Ltd | Construction | 2021 |
| Oakley Healthcare & Mobility Ltd | Wholesale & retail | 2023 |
| Oaklow Group Darlow Lettings Ltd | Real estate | 2018 |
| Oaklow Group Darlow Suter Ltd | Real estate | 2023 |
| Oaklow Group Little Addington Ltd | Construction | 2020 |
| Oakmed Holdings Limited | Professional & scientific | 2004 |
| Oakmount Global Ltd | Professional & scientific | 2022 |
| Oaks and Friends Ltd | Manufacturing | 2025 |
| Oakstead Developments Ltd | Real estate | 2022 |
| Oakstone Finance Ltd | Financial services | 2025 |
| Oakwood Scaffolding Limited | Construction | 2014 |
| Oakwood Wealth Management Limited | Professional & scientific | 2008 |
| Oakwoods Care Group Ltd | Health & social care | 2023 |
| OAL Holdings Limited | Financial services | 2016 |