| NVR Security Ltd | Administrative & support | 2026 |
| NWB Builds Ltd | Real estate | 2024 |
| NWZ Properties Ltd | Real estate | 2021 |
| NXT LVL Tech Ltd | Information & communication | 2024 |
| NY Construction Ltd | Construction | 2005 |
| NY Forestry Ltd | Agriculture & fishing | 2008 |
| NY91 Limited | Administrative & support | 2020 |
| Nyhse Ltd | Professional & scientific | 2023 |
| O Mccabe Ltd | Information & communication | 2009 |
| O&G Solutions (North East) Ltd | Construction | 2019 |
| O&I Offshore Ltd | Construction | 2025 |
| O'Brien Carpet Cleaning Limited | Other services | 2015 |
| O'Brien Residential Properties Ltd | Real estate | 2017 |
| O'Connells Irish Bars Limited | Hospitality | 2011 |
| O'Connells Middlesbrough Limited | Hospitality | 2019 |
| O'Domhnaill Ltd | Professional & scientific | 2025 |
| O'Donnell Offshore Limited | Professional & scientific | 2018 |
| O'Donnell Property Holdings Ltd | Real estate | 2017 |
| O'Dowds Ltd | Professional & scientific | 2024 |
| O'Farrell & Sons Limited | Administrative & support | 2025 |
| O.Bezemer Building & Joinery Limited | Construction | 2015 |
| Oak Connexions Limited | Wholesale & retail | 2017 |
| Oakbridge Enterprise Ltd | Wholesale & retail | 2025 |
| Oakwood North Limited | Real estate | 2026 |
| Oakwood RM1 Limited | Administrative & support | 2022 |
| Oana Hama Car Wash Ltd | Administrative & support | 2022 |
| Oana.Cristina.Care Limited | Health & social care | 2018 |
| OAO Engineering Limited | Professional & scientific | 2023 |
| Obern Property Limited | Real estate | 2024 |
| Oberon & Omega Ltd | Arts & recreation | 2025 |
| OBR Projex Limited | Professional & scientific | 2024 |
| Observer Interactive Ltd | Information & communication | 2023 |
| OC - Insulations Ltd | Construction | 2025 |
| Occupational Therapy Hub Limited | Health & social care | 2017 |
| Oceanic Stores and Deck Solutions Ltd | Transport & logistics | 2025 |
| Oceanz NE Limited | Administrative & support | 2024 |
| Octavo Limited | Administrative & support | 2024 |
| ODB Rigging Ltd | Information & communication | 2022 |
| Odiset Limited | Administrative & support | 2024 |
| OEO Investments Limited | Real estate | 2025 |
| Office Electrix Ltd | Construction | 2017 |
| Offshore Access (NE) Limited | Professional & scientific | 2019 |
| Offshore Commercial Solutions Ltd | Professional & scientific | 2017 |
| Offshore Rigging & Lifting Services Ltd | Construction | 2019 |
| Offshoreriggingservices Ltd | Construction | 2025 |
| OG Instrument Consultants Ltd | Professional & scientific | 2022 |
| Ogenaz Limited | Information & communication | 2023 |
| Ognr Compliance Limited | Mining & quarrying | 2018 |
| OH Bailey Ltd | Manufacturing | 2023 |
| OH SO Linked Limited | Wholesale & retail | 2025 |
| OH SO Locks Ltd | Wholesale & retail | 2018 |
| OIL North East Services Limited | Wholesale & retail | 2023 |
| OJH Cars Limited | Wholesale & retail | 2023 |
| OKJ Active Ltd | Wholesale & retail | 2025 |
| Olam Care Services Ltd | Real estate | 2020 |
| OLC Electrical Limited | Construction | 2022 |
| Old Moon Ltd | Arts & recreation | 2026 |
| Oliflex Future Limited | Real estate | 2021 |
| Olivello Ltd | Hospitality | 2017 |
| Olivitos and Catering Ltd | Hospitality | 2024 |
| Olivitos UK 2 Limited | Professional & scientific | 2019 |
| Olml Ltd | Construction | 2023 |
| Olompik Bistro Ltd | Hospitality | 2023 |
| Olsen Analysis Limited | Information & communication | 2025 |
| OLY Food Limited | Hospitality | 2023 |
| Omega Apothecaries Ltd | Financial services | 2023 |
| Omega Keystone Solutions Ltd | Real estate | 2023 |
| Omega Metal Recycling Limited | Wholesale & retail | 2020 |
| Omid Constructions Limited | Construction | 2025 |
| Omnexa Ltd | Wholesale & retail | 2025 |
| Omni Fade Ltd | Other services | 2024 |
| Omni Global Ventures Ltd. | Wholesale & retail | 2025 |
| Omnia Interactive Limited | Information & communication | 2016 |
| Omnibus Ltd | Extraterritorial | 2024 |
| Omniplay Games Ltd | Information & communication | 2019 |
| Omnis Communications Ltd | Construction | 2021 |
| Omt/Neverstress Ltd | Professional & scientific | 2026 |
| ON & Offshore Rigging & Lifting Limited | Professional & scientific | 2011 |
| ON a Roll Sandwich Company Limited | Manufacturing | 2006 |
| ON Point Commercial Aluminium Limited | Wholesale & retail | 2016 |
| ON Track (NE) Limited | Transport & logistics | 2024 |
| One Competition Ltd | Arts & recreation | 2025 |
| One Life Foundation | Other services | 2019 |
| One MAN and HIS Fridge CIC | Administrative & support | 2025 |
| One Moment in Time Photo & Film Ltd | Information & communication | 2023 |
| One Rhythm Music Ltd | Hospitality | 2025 |
| One Soul Clothing Ltd | Wholesale & retail | 2023 |
| One Step Limited | Information & communication | 2025 |
| One Stop Beauty M Ltd | Other services | 2023 |
| Oneapphome Limited | Administrative & support | 2022 |
| Oneill Brooke Limited | Real estate | 2025 |
| Onetran (Teesside) Ltd | Construction | 2025 |
| Ongo BIO Ltd | Agriculture & fishing | 2020 |
| Onine Global Innovations Ltd | Transport & logistics | 2024 |
| Onisimcristi Ltd | Transport & logistics | 2025 |
| ONL Project Services Limited | Professional & scientific | 2016 |
| Online Training Academy by Stephanie Ltd | Education | 2020 |
| Only Faces Ltd | Other services | 2023 |
| Only Glands Ltd | Construction | 2026 |
| Onslaught SUB Limited | Construction | 2012 |