| Olive Photography Ltd | Professional & scientific | 2024 |
| Oliver’S Estate and Management Limited | Real estate | 2024 |
| Olivia Byrne Limited | Hospitality | 2024 |
| Ollerhead Electrical Isolation's Ltd. | Construction | 2017 |
| Olumide ESE Limited | Professional & scientific | 2017 |
| Omega Atlantic Ltd | Administrative & support | 1998 |
| Omega Properties (Wirral) Limited | Real estate | 2022 |
| Omega Red Solutions Limited | Construction | 2024 |
| OMO Stores Limited | Wholesale & retail | 2009 |
| Omori Machinery UK Ltd | Manufacturing | 1945 |
| ON the Banks of the Royal Blue Mersey Limited | Arts & recreation | 2017 |
| Onchan Medical Limited | Health & social care | 2021 |
| One Crafty COW Ltd | Hospitality | 2024 |
| One Cross Care Ltd | Health & social care | 2024 |
| One Stop Safety Supplies Ltd | Wholesale & retail | 2026 |
| One Yachtie Ltd | Wholesale & retail | 2021 |
| Onefast Ltd | Administrative & support | 2021 |
| Onehealth Applications Ltd | Professional & scientific | 2026 |
| ONEOFTHE8 Ltd | Information & communication | 2021 |
| Onesource Property Solutions Ltd | Administrative & support | 2026 |
| Online Direct Stores Ltd | Wholesale & retail | 2024 |
| Open Thoughts Ltd | Other services | 2022 |
| Openbook Bookkeeping Services Limited | Professional & scientific | 2009 |
| Openfolk CIC | Education | 2025 |
| Openhouse Holdings Limited | Financial services | 2020 |
| Ophidian Audio Limited | Manufacturing | 2011 |
| Opia Trading Ltd | Wholesale & retail | 2025 |
| Opmed Industries Limited | Manufacturing | 2018 |
| Opportuned Ltd | Education | 2023 |
| Opscon Accountancy Ltd | Professional & scientific | 2024 |
| Optigram Ltd | Wholesale & retail | 2022 |
| Optima Consultants Limited | Extraterritorial | 2015 |
| Optima Heart Health Ltd | Other services | 2024 |
| Optima Reliability Limited | Administrative & support | 2017 |
| Optimal Heating Ltd | Construction | 2022 |
| Optus Resin Limited | Manufacturing | 2019 |
| Optymyse Ltd | Information & communication | 2024 |
| Opulent Plumbing & Heating Ltd | Construction | 2021 |
| Opus 4 Limited | Professional & scientific | 2012 |
| Oracle Ophthalmic Distribution Services Ltd. | Financial services | 2021 |
| Orchard Meadows (Appleton) Management Company Limited | Households | 2021 |
| Orchard Place Freehold Ltd | Administrative & support | 2016 |
| Orchard Place RTM Company Ltd | Real estate | 2009 |
| Orchestrate Properties Limited | Real estate | 2017 |
| Orchid Rock North Ltd | Real estate | 2025 |
| Ordotics Ltd | Information & communication | 2018 |
| Organic Bros Ltd | Hospitality | 2019 |
| Organon Health Ltd | Professional & scientific | 2022 |
| Oriel Court (Prenton) Management Company Limited | Real estate | 2006 |
| Origin Cotton Consulting Ltd | Professional & scientific | 2026 |
| Origin Cotton Ltd | Professional & scientific | 2026 |
| Orphan Village Africa Ltd | Other services | 2007 |
| Orwell Engineering Solutions Limited | Manufacturing | 2009 |
| Orwell Lift Finishes Limited | Manufacturing | 2009 |
| OS Living Limited | Households | 2025 |
| Osbh Limited | Health & social care | 2023 |
| Osprey EMS Ltd | Health & social care | 2023 |
| Osteopathy & Natural Health Clinic Limited | Health & social care | 2007 |
| Otdm Ltd | Information & communication | 2024 |
| Otectics Ltd | Information & communication | 2021 |
| Otoni Assets Limited | Information & communication | 2025 |
| Otoni Limited | Financial services | 2024 |
| Otoni Projects Limited | Information & communication | 2009 |
| Otto Estates Ltd | Real estate | 2022 |
| Oudvana Limited | Wholesale & retail | 2025 |
| Oulton Productions Limited | Arts & recreation | 2026 |
| OUR Coffee Shop Ltd | Hospitality | 2018 |
| OUR Lady of Pity Preschool CIC | Education | 2020 |
| OUT of Hours Solutions Limited | Other services | 2022 |
| OUT Today Ltd | Administrative & support | 2026 |
| Outboard& Marine Ltd | Transport & logistics | 2015 |
| Outfit Marine Ltd | Construction | 2012 |
| Outfitt Ltd | Information & communication | 2025 |
| Outreach Physio Ltd | Health & social care | 2014 |
| Outworx Exterior Cleaning and Maintenance Limited | Administrative & support | 2025 |
| Outwrite Public Relations Limited | Professional & scientific | 2000 |
| Ovalrest Limited | Professional & scientific | 1974 |
| Overseas Student Placement Services Ltd | Education | 2021 |
| Overstrand Management Company Limited | Households | 1988 |
| Overton Community Centre Ltd | Real estate | 2010 |
| OW Much Design Ltd | Professional & scientific | 2022 |
| Owen Drew Ltd | Manufacturing | 2024 |
| Owen Matthews Ltd | Arts & recreation | 2019 |
| Owlspire International Academy Ltd | Professional & scientific | 2025 |
| Owning Life Ltd | Real estate | 2019 |
| Oxenby Property Limited | Real estate | 2024 |
| Oxford Life Science Ltd | Professional & scientific | 2016 |
| Oxton Cuisine Group Limited | Hospitality | 2025 |
| Oxton Landscape Limited | Administrative & support | 2014 |
| Ozan Broadway Ltd | Hospitality | 2024 |
| P & C Housing Solutions Limited | Real estate | 2018 |
| P & E Property Lettings Ltd | Real estate | 2024 |
| P & K Aviation Ltd | Manufacturing | 2019 |
| P a F Media Sales Limited | Professional & scientific | 2006 |
| P a Johnson Transport Logistics Ltd | Transport & logistics | 2018 |
| P Airey Tail Lifts Limited | Administrative & support | 2009 |
| P and K Wirral Homes Ltd | Real estate | 2021 |
| P D K Project Engineering Limited | Professional & scientific | 1995 |
| P Fenn Property Services Limited | Construction | 2018 |
| P R P M Services Limited | Administrative & support | 2015 |