| Onyx Structural Ltd | Professional & scientific | 2021 |
| Onyx Thrills Ltd | Wholesale & retail | 2025 |
| OOK Design & Marketing Agency Ltd | Professional & scientific | 2015 |
| Ooshu Limited | Information & communication | 2023 |
| Opal Property Ltd | Real estate | 2017 |
| Open Door (North East) | Other services | 2003 |
| Open Door Art CIC | Arts & recreation | 2023 |
| Open Door North East Enterprise Limited | Administrative & support | 2026 |
| Open Gate Yorkshire Limited | Hospitality | 2024 |
| Open Health Limited | Health & social care | 2016 |
| Open Source AI Ltd | Information & communication | 2025 |
| Opera Nova | Arts & recreation | 2006 |
| Opero Systems Limited | Information & communication | 2012 |
| Opportunitees Limited | Education | 2015 |
| Optic Systems Ltd | Information & communication | 2026 |
| Opticlean Windows Ltd | Administrative & support | 2021 |
| Optima Web UK Ltd | Information & communication | 2025 |
| Optime Limited | Information & communication | 2019 |
| Optimum Pest Control Services Limited | Administrative & support | 2019 |
| Optimums Innovations Limited | Wholesale & retail | 2025 |
| Opulence Property Limited | Real estate | 2025 |
| OR BIT IS Limited | Information & communication | 2008 |
| Oracle Group Ltd | Hospitality | 2026 |
| Oral Health Daily Limited | Wholesale & retail | 2020 |
| Oralcare Compare Ltd | Administrative & support | 2021 |
| Orangewheels Limited | Wholesale & retail | 2007 |
| Orbis Immersive Limited | Information & communication | 2018 |
| Orbit Integrated Care Services Ltd | Administrative & support | 2023 |
| Orbita Solutions Ltd | Wholesale & retail | 2011 |
| Orchid Engineering Services Ltd | Professional & scientific | 2014 |
| Orchid Technologies Limited | Information & communication | 2021 |
| Ordy Ltd | Information & communication | 2025 |
| Orient Spaces Renovations Ltd. | Construction | 2025 |
| Oriental Pearl Nunthorpe Ltd | Hospitality | 2024 |
| Orion Lighting Limited | Wholesale & retail | 2025 |
| Orion Lighting Services Limited | Construction | 2025 |
| Orion VUE Estates Limited | Real estate | 2024 |
| Orkney Renovations Ltd | Construction | 2024 |
| Orleans Capital Ltd | Financial services | 2021 |
| Orme Engineering Limited | Professional & scientific | 2019 |
| Ormesby Carpets and Flooring Ltd | Wholesale & retail | 2020 |
| Ormesby Cars Ltd | Wholesale & retail | 2024 |
| Ormesby Convenience Store Ltd | Wholesale & retail | 2026 |
| Orooka Ltd | Information & communication | 2026 |
| Orsobiancosurfacedesign Ltd | Professional & scientific | 2026 |
| Orvizta Ltd | Wholesale & retail | 2025 |
| Oscar & Tilly Limited | Wholesale & retail | 2017 |
| Oscar's Bozo Ltd | Other services | 2025 |
| Osteoarthritisaudioprescription Limited | Health & social care | 2016 |
| Ostorf Limited | Real estate | 2022 |
| Oswell Technologies Limited | Information & communication | 2025 |
| Otaka Ltd | Information & communication | 2026 |
| OTC (NE) Limited | Administrative & support | 2010 |
| Otis Holdings Northern Limited | Financial services | 2021 |
| OTL (NE) Limited | Professional & scientific | 2022 |
| Otseq Ltd | Information & communication | 2022 |
| Oulton Holdings Limited | Financial services | 2025 |
| OUR Children 1ST | Education | 2017 |
| OUT of This World Limited | Professional & scientific | 2016 |
| Outcut Ltd | Administrative & support | 2026 |
| Outline Prototype Services Ltd | Manufacturing | 2017 |
| Outrage Fitness Limited | Wholesale & retail | 2001 |
| Outrank Limited | Information & communication | 2018 |
| Outright Property Partners Ltd | Real estate | 2022 |
| Outshine Gaming 26 Ltd | Wholesale & retail | 2026 |
| Outsource Your Finance Limited | Professional & scientific | 2007 |
| Ouya Properties Limited | Real estate | 2023 |
| Over Ice Trading Ltd | Wholesale & retail | 2019 |
| Overload Interactive Limited | Information & communication | 2026 |
| Owton Fisheries Ltd | Wholesale & retail | 2021 |
| OXF Retail Ltd | Wholesale & retail | 2021 |
| Oxford Investment Properties Ltd | Real estate | 2025 |
| Oxley Property Developments Limited | Real estate | 2018 |
| Oxley Rentals Limited | Real estate | 2023 |
| Oxley Retail Ltd | Wholesale & retail | 2024 |
| OYA Engineering Ltd | Professional & scientific | 2026 |
| P & F Hammond Limited | Hospitality | 2020 |
| P & G Rigging Solutions Ltd | Construction | 2026 |
| P & L Developments Limited | Professional & scientific | 2015 |
| P & P Protective Coatings Limited | Public administration | 2023 |
| P & S Initiatives Limited | Hospitality | 2017 |
| P C I Holdings (NE) Ltd | Wholesale & retail | 2017 |
| P Foodstore NE Ltd | Wholesale & retail | 2022 |
| P J Collins Property Ltd | Real estate | 2024 |
| P K B Inspection Services Ltd | Manufacturing | 2020 |
| P M Services UK Ltd | Administrative & support | 2006 |
| P Mccarthy Safety Services Ltd | Professional & scientific | 2025 |
| P R K Joinery Limited | Manufacturing | 2009 |
| P S Knight Offshore Ltd | Manufacturing | 2014 |
| P&A Compliance Limited | Professional & scientific | 2023 |
| P&A Consultancy Services Limited | Administrative & support | 2018 |
| P&D Industrial Coatings Ltd | Construction | 2021 |
| P&J Access Safety Ltd | Professional & scientific | 2023 |
| P&S Tech Services Limited | Energy | 2024 |
| P+Hs Architects Limited | Professional & scientific | 2004 |
| P. Dawson & SON Limited | Construction | 2009 |
| P. M. Solutions (South East) Limited | Construction | 2017 |
| P.A.A Property's Limited | Real estate | 2021 |
| P.C. Tech (Normanby) Limited | Information & communication | 2014 |
| P.H. Skerry Ltd. | Construction | 1991 |