| OAR Properties Limited | Real estate | 2002 |
| Oasis Catering Management Ltd | Education | 2025 |
| Oasis Hospitality Management Ltd | Education | 2025 |
| Oasis NCL Limited | Wholesale & retail | 2025 |
| Oasis Shisha Lounge Limited | Hospitality | 2013 |
| Oates Ltd | Real estate | 2019 |
| OB Group Limited | Other services | 2016 |
| Obbyco Ltd. | Information & communication | 2016 |
| Obikpo Ltd | Health & social care | 2025 |
| OBR Real Estate Limited | Real estate | 2020 |
| Obravenewstory Ltd | Education | 2026 |
| Obrien Nationwide Ames Taping Contractors Ltd | Construction | 2009 |
| Observatori Creative Ltd | Information & communication | 2025 |
| Obsidian Crest Ltd | Administrative & support | 2025 |
| Obsidian Finish Ltd | Wholesale & retail | 2025 |
| Obvious Agency Ltd | Real estate | 2023 |
| OC Accountants Ltd | Professional & scientific | 2012 |
| OC1 (NE) Limited | Hospitality | 2023 |
| OC10 (NE) Limited | Hospitality | 2024 |
| OC11 (NE) Limited | Hospitality | 2025 |
| OC2 (NE) Limited | Hospitality | 2023 |
| OC3 (NE) Limited | Hospitality | 2023 |
| OC399715 LLP | | 2015 |
| OC4 (NE) Limited | Hospitality | 2023 |
| OC5 (NE) Limited | Hospitality | 2023 |
| OC6 (NE) Limited | Hospitality | 2023 |
| OC8 (NE) Ltd | Hospitality | 2023 |
| OC9 (NE) Limited | Hospitality | 2023 |
| OCD Technical Ltd | Manufacturing | 2022 |
| Ocean 3D (North East) Ltd | Professional & scientific | 2025 |
| Ocean Fish & Chips Sunderland Ltd | Hospitality | 2023 |
| Ocean Hand Car Wash Ltd | Wholesale & retail | 2018 |
| Ocean of Knowledge Ltd | Education | 2025 |
| Ocean Road Rental Limited | Real estate | 2025 |
| Ocean Sales and Marketing Solutions Ltd | Wholesale & retail | 2020 |
| Ocean Ship Services Limited | Construction | 2013 |
| Ocean Star Red ROW Limited | Hospitality | 2022 |
| Oceana Business Park Limited | Hospitality | 2013 |
| Oceandeep AI Ltd | Information & communication | 2024 |
| Oceans Wealth Ltd | Real estate | 2025 |
| Oceantek Limited | Energy | 2024 |
| OCH Holdings Ltd | Financial services | 2024 |
| Ocho Alfa Limited | Wholesale & retail | 2022 |
| Ochre Yards Block 10 Management Company Limited | Real estate | 2017 |
| Ochre Yards Eleven Limited | Real estate | 2004 |
| Ochre Yards Five Limited | Real estate | 2005 |
| Ochre Yards One Limited | Real estate | 2003 |
| Ochre Yards SIX Limited | Real estate | 2007 |
| Ochre Yards Three Limited | Households | 2003 |
| Ochunuel Property Maintenance Limited | Construction | 2025 |
| Ockham Partners Ltd | Information & communication | 2020 |
| Ocrex UK Ltd | Professional & scientific | 2012 |
| Ocs-Uk IT Holdings Ltd | Financial services | 2021 |
| Octagon Partners Ltd | Real estate | 2015 |
| Octas Power Limited | Manufacturing | 2026 |
| Octaweb Limited | Information & communication | 2024 |
| October House Training Limited | Professional & scientific | 2012 |
| Octopus Corporation Limited | Real estate | 2010 |
| Octopus Media Ltd | Information & communication | 2008 |
| Octopus Media Newcastle Ltd | Professional & scientific | 2019 |
| Octopus Property Limited | Real estate | 2010 |
| Octopus Renovation Limited | Real estate | 2013 |
| Octopus Traders Limited | Wholesale & retail | 2017 |
| Octothorpe Kimmins Ltd | Professional & scientific | 2022 |
| Octric Semiconductors Limited | Manufacturing | 2016 |
| Ocucon A.I. Limited | Administrative & support | 2025 |
| Ocucon Limited | Administrative & support | 2016 |
| Ocucon Pixelate Limited | Administrative & support | 2025 |
| Ocular Systems Ltd | Manufacturing | 2024 |
| Odaf Eco Services Limited | Extraterritorial | 2025 |
| Odag Consultants Limited | Information & communication | 2016 |
| ODD Bott and Balls Ltd | Arts & recreation | 2024 |
| Oddarra Ltd | Health & social care | 2023 |
| Oddity Studios Limited | Arts & recreation | 2019 |
| Odie's Treats Ltd | Wholesale & retail | 2024 |
| Odins Estates Ltd | Real estate | 2025 |
| Odins Medical Ltd. | Health & social care | 2020 |
| ODL & Father Gosforth Ltd | Other services | 2023 |
| Odontologo Ltd | Administrative & support | 2023 |
| OEP Inc Ltd | Health & social care | 2023 |
| OFC Foods Ltd | Hospitality | 2025 |
| OFF Road NE Ltd | Wholesale & retail | 2023 |
| OFF Side Local Ltd | Wholesale & retail | 2026 |
| OFF the Grid Adventures C.I.C. | Education | 2020 |
| OFF the Wall Limited | Extraterritorial | 1995 |
| Offbeat Global Support System Ltd | Real estate | 2022 |
| Offerconnect Ltd | Education | 2024 |
| Office Supplies North East Ltd | Manufacturing | 2017 |
| Offshore Consultant North East Ltd | Professional & scientific | 2026 |
| Offshore Engineering and Management Ltd | Professional & scientific | 2023 |
| Offshore Hub Ltd | Arts & recreation | 2024 |
| Offshore Workforce Ltd | Professional & scientific | 2013 |
| OG - Make a Move Ltd | Construction | 2025 |
| OG Socks Ltd | Wholesale & retail | 2019 |
| OG White Limited | Transport & logistics | 2018 |
| Oglander Consulting Limited | Professional & scientific | 2021 |
| OH1 Properties Ltd | Other services | 2022 |
| Ohall Ltd | Manufacturing | 2018 |
| Ohana Consultants Ltd | Professional & scientific | 2020 |
| Ohvu Ltd | Information & communication | 2026 |