| Oasis Care Solutions NW Ltd | Health & social care | 2023 |
| Oasis Guest House Blackpool Limited | Hospitality | 2015 |
| Objectb Limited | Information & communication | 2011 |
| Obodo Ltd | Information & communication | 2025 |
| Obsolete Electrical Supplies Ltd | Construction | 2009 |
| Occupational Health International Limited | Health & social care | 1998 |
| Occupational Health Recruitment Limited | Administrative & support | 2021 |
| Ocean Bay Blackpool Ltd | Hospitality | 2024 |
| Ocean Boulevard II Limited | Hospitality | 2002 |
| Ocean Boulevard III Limited | Hospitality | 2017 |
| Ocean Care Services Ltd | Health & social care | 2020 |
| Ocean Palace (Lancashire) Ltd | Hospitality | 2002 |
| Ocean Youth Ltd | Wholesale & retail | 2025 |
| Oceanmaster Marine Limited | Extraterritorial | 2023 |
| OCH Electrical Ltd | Mining & quarrying | 2017 |
| OCR Motor Limited | Wholesale & retail | 2024 |
| Octagan Limited | Professional & scientific | 2007 |
| Oddle Entertainment Agency Ltd | Arts & recreation | 2019 |
| Odds on Competitions Limited | Wholesale & retail | 2026 |
| Odin Events Limited | Arts & recreation | 2010 |
| Odisea Travel Ltd | Administrative & support | 2024 |
| Odus Pinnacle(Uk) Limited | Transport & logistics | 2025 |
| Ofero Limited | Wholesale & retail | 2025 |
| OFF Piste Acquisitions Limited | Real estate | 2017 |
| OFF YOU POP Ltd | Wholesale & retail | 2026 |
| Office Plan UK Limited | Real estate | 2008 |
| Officestore UK Limited | Other services | 2019 |
| Offigouk Ltd | Information & communication | 2016 |
| Og's Acre Limited | Wholesale & retail | 2025 |
| Ogden (Transteel) Limited | Wholesale & retail | 1987 |
| OHI Health Essentials Ltd | Health & social care | 2024 |
| Ohmega Electrical Services Limited | Construction | 2015 |
| OJ Creative Ltd | Professional & scientific | 2023 |
| OK Breakers Ltd | Construction | 2020 |
| Okian Limited | Information & communication | 2001 |
| Old Bankfield Limited | Real estate | 2014 |
| Old Farm Garage Ltd | Wholesale & retail | 2025 |
| Old Stamp House Ambleside Ltd | Households | 2022 |
| Oldland Leisure Limited | Arts & recreation | 1986 |
| Oldroyd Publishing Group Limited | Administrative & support | 1986 |
| Oldroyd Publishing Ltd. | Administrative & support | 1983 |
| Olibe International Ltd | Administrative & support | 2024 |
| Olilo UK & Ireland Ltd | Information & communication | 2025 |
| Olisar Limited | Professional & scientific | 2012 |
| Olive Property & Investment Group Ltd | Real estate | 2026 |
| Oliver's Fossils Limited | Arts & recreation | 2023 |
| Olivia Wilson Consultancy Services Ltd | Information & communication | 2023 |
| Olka Yachting Ltd. | Extraterritorial | 2023 |
| Ollibugs Ltd | Wholesale & retail | 2022 |
| Ollie Cooper Design Ltd | Information & communication | 2018 |
| Olly Pickard Limited | Information & communication | 2013 |
| Olsen Purdy Associates Ltd | Information & communication | 2015 |
| Omega Electrical (North West) Ltd | Construction | 2022 |
| Omega GAS (U.K.) Ltd | Construction | 2005 |
| Omega Holdings NW Ltd | Real estate | 2024 |
| Omer Ikram Ltd | Professional & scientific | 2025 |
| Omoto Healthcare Limited | Health & social care | 2016 |
| Omoto Stores Limited | Wholesale & retail | 2025 |
| Omshakti Consulting Ltd | Information & communication | 2007 |
| ON Call Doctors North-West Limited | Health & social care | 2020 |
| ON the TEE Publications Limited | Professional & scientific | 2021 |
| On-Site Kitchen Rentals Limited | Wholesale & retail | 1998 |
| ON1 Solutions Limited | Information & communication | 2021 |
| Oncallvets Ltd | Other services | 2017 |
| One Chance Care Ltd | Health & social care | 2023 |
| One Fylde | Hospitality | 1995 |
| One Home Property Securities Ltd | Financial services | 2025 |
| One Life Therapy Clinic Ltd | Health & social care | 2013 |
| One of a Kind Design UK Ltd | Manufacturing | 2020 |
| One OFF Services Limited | Administrative & support | 2009 |
| Oneconsultancy Limited | Information & communication | 2015 |
| Onetree Investment Consulting Limited | Information & communication | 2020 |
| Online Medical Supplies Ltd | Wholesale & retail | 2022 |
| Online Searches Limited | Professional & scientific | 2007 |
| Only GAS NW Ltd | Construction | 2025 |
| Only Tans Blackpool Limited | Other services | 2025 |
| Onlyart Ltd | Transport & logistics | 2021 |
| Onpoint Civil Solutions Ltd | Construction | 2024 |
| Onroute Retail Ltd | Wholesale & retail | 2025 |
| Onwards Property Investments Limited | Real estate | 2022 |
| Onyeji Medicare Services Limited | Health & social care | 2024 |
| Onyxx Electronics Ltd | Wholesale & retail | 2026 |
| Ootseo Ltd | Information & communication | 2024 |
| Opal Bloso Beauty Ltd | Wholesale & retail | 2025 |
| Open Creative Events Ltd | Administrative & support | 2025 |
| Open Recruitment Limited | Administrative & support | 2019 |
| Opendoor Publishing Limited | Information & communication | 2020 |
| Opes Lucrum Holdings Ltd | Households | 2025 |
| Oplo Group Ltd | Financial services | 2005 |
| Oplo Holdings Ltd | Financial services | 2016 |
| Opportune Investing Ltd | Real estate | 2016 |
| Opportunity Beckons Consulting Ltd | Information & communication | 2021 |
| Oprea Innovations Ltd | Real estate | 2026 |
| Oprea Properys Ltd | Real estate | 2026 |
| Opsworks Ltd | Health & social care | 2025 |
| Optiaion Ltd | Information & communication | 2024 |
| Optim Tech Ltd | Information & communication | 2025 |
| Optimal Operations Limited | Professional & scientific | 2010 |
| Optimised Buildings Ltd | Professional & scientific | 2006 |
| Optimised Spaces Limited | Administrative & support | 2013 |