| Oakwood Motor Company Limited | Wholesale & retail | 2006 |
| Oakwood Primary Ltd | Education | 2026 |
| OAR Electrical Services Ltd | Construction | 2026 |
| Oasis Business Park Ltd | Households | 2017 |
| Oasis European Missions Limited | Education | 2022 |
| Oasis Health and Wellness Group Limited | Health & social care | 2021 |
| Oasis Investments MCR Ltd | Real estate | 2021 |
| OAT Interiors Limited | Professional & scientific | 2025 |
| Obake Clothing Ltd | Wholesale & retail | 2024 |
| OBD Tech Ltd | Wholesale & retail | 2025 |
| OBD Tech Solutions Ltd | Wholesale & retail | 2025 |
| OBG Developments Limited | Professional & scientific | 2016 |
| OBH Trading Ltd | Wholesale & retail | 2025 |
| Occupy Property Ltd | Real estate | 2014 |
| Ocean Fish Bar Inc Ltd | Hospitality | 2023 |
| OCF332 Limited | Wholesale & retail | 2021 |
| Ochano Ltd | Wholesale & retail | 2025 |
| Ochiworlduk Limited | Wholesale & retail | 2021 |
| Ochmere Limited | Professional & scientific | 2020 |
| OCI (Chorley) Ltd | Real estate | 2026 |
| Ocon Groundworks Ltd | Construction | 2018 |
| OCS GAS Solutions Limited | Construction | 2025 |
| Octane Vehicle Leasing Ltd | Administrative & support | 2020 |
| Octavia Coaching Ltd | Professional & scientific | 2024 |
| Octo Fire Ltd | Professional & scientific | 2026 |
| Octo Scaffolding Limited | Construction | 2015 |
| Odaya Ltd | Construction | 2025 |
| ODD Little Cat Ltd | Professional & scientific | 2022 |
| Odni Anisky Ltd | Wholesale & retail | 2025 |
| Oerich Ltd | Wholesale & retail | 2019 |
| OFF the Rails Clothing Ltd | Wholesale & retail | 2017 |
| Officenut Limited | Wholesale & retail | 2000 |
| OGV Taproom Limited | Manufacturing | 2019 |
| Ohms Law Electrical Ltd | Construction | 2024 |
| Ohpi Property Limited | Construction | 2019 |
| Okane NW Ltd | Hospitality | 2024 |
| OL10 Ltd | Other services | 2024 |
| Old (SES) Limited | Manufacturing | 1948 |
| Old DUN Horse (Ramsbottom) Ltd | Households | 2023 |
| Old River Garden Services Ltd | Administrative & support | 2023 |
| Olifra Ltd | Wholesale & retail | 2019 |
| Olive & Peck Holdings Ltd | Real estate | 2023 |
| Olive Green Ltd. | Financial services | 2018 |
| Olive Restaurant and Bar Limited | Hospitality | 2024 |
| Olive Tree Jewish Nursery Ltd | Health & social care | 2024 |
| Olive's Kitchen (Bury) Limited | Hospitality | 2020 |
| Olivecap Holdings Ltd | Financial services | 2025 |
| Oliver Brazier Ltd | Construction | 2017 |
| Olivia Alice MUA Limited | Other services | 2016 |
| Olivia Clinic Academy Limited | Education | 2024 |
| Olivia Clinic Limited | Other services | 2024 |
| Omega Couriers Limited | Transport & logistics | 2021 |
| Omniops Ltd | Professional & scientific | 2025 |
| ON Retail Store Ltd | Wholesale & retail | 2025 |
| ON Track Breakdown Ltd | Transport & logistics | 2026 |
| ON Travels Limited | Wholesale & retail | 2021 |
| ONA Trading Ltd | Hospitality | 2024 |
| Once Wear Limited | Wholesale & retail | 2024 |
| Oncueai Ltd | Administrative & support | 2025 |
| One Business Cover Limited | Financial services | 2015 |
| One Day Films Limited | Information & communication | 1996 |
| One Funding Ltd | Financial services | 2023 |
| One Step Bury CIC | Health & social care | 2020 |
| One&All Wellness Ltd | Manufacturing | 2025 |
| Oneness Foundation | Other services | 2018 |
| Oneshot Trials Ltd | Administrative & support | 2025 |
| ONI Tattoo Collective Ltd | Other services | 2025 |
| ONJ Goods Ltd | Wholesale & retail | 2023 |
| Online Therapy Solutions Ltd | Health & social care | 2022 |
| Online Web Hosting Ltd | Information & communication | 2021 |
| Onlinemasonry Ltd | Construction | 2023 |
| ONR Online Ltd | Wholesale & retail | 2019 |
| Onside Sports Management Limited | Other services | 2002 |
| Onto Consultancy Ltd | Professional & scientific | 2024 |
| Onyx Bookings Ltd | Professional & scientific | 2023 |
| Onyx Fitness Ramsbottom Ltd | Arts & recreation | 2024 |
| OPA Projects Ltd | Professional & scientific | 2022 |
| Open Pharmacy Ltd | Wholesale & retail | 2025 |
| Open Wellness Ltd | Information & communication | 2026 |
| Opes Liverpool Ltd | Water & waste | 2023 |
| OPM International Ltd | Extraterritorial | 2008 |
| Optics 85 Ltd | Health & social care | 2024 |
| Optima DEV Ltd | Administrative & support | 2020 |
| Optimal Employment Law Limited | Professional & scientific | 2019 |
| Optimum Coaching Ltd | Other services | 2025 |
| Oqaab Ltd | Administrative & support | 2024 |
| Oram Street Transport Limited | Professional & scientific | 1982 |
| Orange Skips (NW) Ltd | Water & waste | 2021 |
| Orchard House Management (Worsley) Limited | Households | 2016 |
| Organic Code Limited | Information & communication | 2023 |
| Orgolf Limited | Wholesale & retail | 2024 |
| Orgolf Wear Limited | Wholesale & retail | 2024 |
| Orgstream Limited | Manufacturing | 2012 |
| Orient Destination Management Company Limited | Administrative & support | 2021 |
| Original Gyros Ltd | Hospitality | 2023 |
| Origo Care Ltd | Health & social care | 2026 |
| Orion Electrical Services (NW) Ltd | Construction | 2024 |
| Orion Networks Manchester Ltd | Information & communication | 2024 |
| Orioncrown Limited | Wholesale & retail | 1980 |
| Orixa Group Ltd | Wholesale & retail | 2026 |