| Olorun-Jedalo Ltd | Health & social care | 2015 |
| Omega Portugal Ltd | Construction | 2015 |
| Omega Urology Limited | Health & social care | 2022 |
| OMEGA1 Contracts Limited | Construction | 2022 |
| Omg's Kitchen Limited | Hospitality | 2024 |
| Omnia Sports and Entertainment Limited | Professional & scientific | 2020 |
| ON Cloud K9 Ltd | Other services | 2023 |
| On-Site Training and Assessment Ltd | Education | 2014 |
| ONA Strategies Limited | Professional & scientific | 2025 |
| OND Property Ltd | Real estate | 2025 |
| One Argyle Road Management Co Limited | Households | 2009 |
| One Business Solutions (North West) Limited | Other services | 2011 |
| One Call Taxis Ltd | Transport & logistics | 2017 |
| One COD Investments Ltd | Hospitality | 2022 |
| One COD Ltd | Hospitality | 2019 |
| One COD Trading Ltd | Hospitality | 2020 |
| One Fish Company Ltd | Manufacturing | 2011 |
| One Knowsley Road RTM Company Limited | Households | 2013 |
| One Media Solutions Limited | Information & communication | 2012 |
| One Shore Road (Southport) Limited | Real estate | 2016 |
| One Stop Solutions AV Ltd | Professional & scientific | 2022 |
| One Twenty Consulting Ltd | Professional & scientific | 2019 |
| One White Ltd | Financial services | 2024 |
| One World Travel Limited | Administrative & support | 2015 |
| Onepeterfour Limited | Administrative & support | 2016 |
| Oneplan Software Ltd | Information & communication | 2018 |
| Onome Own Limited | Health & social care | 2014 |
| Ontime-Partners Ltd | Health & social care | 2019 |
| Ooshka BA Limited | Hospitality | 2025 |
| Opal Hair Company Limited | Other services | 2025 |
| Open Brewers Limited | Hospitality | 2017 |
| Openbank Innovation Limited | Information & communication | 2019 |
| OPS Outsourced Ltd | Information & communication | 2025 |
| Optasia Wealth Management Limited | Financial services | 2009 |
| Optima Construction Consultants Ltd | Construction | 2026 |
| Optimal Mortgage Ltd | Financial services | 2025 |
| Optimum CIS Limited | Professional & scientific | 2019 |
| Optimum Shine Window Cleaning Ltd | Administrative & support | 2021 |
| Optimum Training Solutions UK Ltd | Financial services | 2023 |
| Optiquality (Holdings) Limited | Real estate | 1942 |
| Optiquality Limited | Extraterritorial | 1999 |
| Opulence Event Staff Ltd | Administrative & support | 2024 |
| Opulenta Procurement Limited | Other services | 2020 |
| OR NW Ltd | Construction | 2015 |
| ORA Talent Ltd | Administrative & support | 2025 |
| Oracle Wind Limited | Manufacturing | 2024 |
| Orchard Developments (NW) Limited | Real estate | 2019 |
| Orchard Hill Advisory Limited | Extraterritorial | 2025 |
| Organic Clients Agency Ltd | Professional & scientific | 2021 |
| Origami Pulse CIC | Arts & recreation | 2018 |
| Original SFC Limited | Hospitality | 2024 |
| Orion Facilities Limited | Information & communication | 2019 |
| Ormsby of DUN Laoghaire Limited | Manufacturing | 1985 |
| Ormskirk Carpet Centre Limited | Wholesale & retail | 1990 |
| Ormskirk Developments Limited | Real estate | 1999 |
| Ormskirk Grammar School Management Company Limited | Households | 2006 |
| Ormskirk Plumbing Ltd | Construction | 2015 |
| Ornap Limited | Health & social care | 2025 |
| OS Construction (SW) Limited | Construction | 2019 |
| Oscar Garage (Southport) Limited | Wholesale & retail | 2016 |
| OT Pathways Limited | Health & social care | 2026 |
| Otec Services Ltd | Construction | 2016 |
| Others Media Ltd | Manufacturing | 2024 |
| OTS (Onthespot) News.Co.Uk Ltd | Information & communication | 2012 |
| Otterstye View RTM Company Limited | Households | 2025 |
| OUI2UK Limited | Professional & scientific | 2024 |
| Ousta Healthcare Services Limited | Health & social care | 2013 |
| Outhwaite & Litherland Ltd | Other services | 2021 |
| Outlook (Hightown) Management Limited(The) | Households | 1979 |
| Outreach (Sefton) Limited | Health & social care | 1999 |
| Overjoyed Ltd | Information & communication | 2025 |
| Owen Jackson Construction Limited | Construction | 2023 |
| OWS Consulting Limited | Financial services | 2025 |
| Oxford Aesthetics (London) Limited | Health & social care | 2017 |
| Oxford Court Residents' Association Limited | Households | 1978 |
| Oxford Traffic Management Ltd | Construction | 2018 |
| Oxlip Education Services Limited | Education | 2025 |
| OYO Bath Street Ltd | Construction | 2019 |
| P & a Audio Visual Ltd | Manufacturing | 1985 |
| P & C Property Group Limited | Households | 2023 |
| P & I Property Investments Limited | Real estate | 2013 |
| P & J Consultancy Associates Ltd | Other services | 2015 |
| P & N Shorrock Associates Limited | Professional & scientific | 2013 |
| P & P Properties (Birkdale) Ltd | Real estate | 2026 |
| P & V Lovie Ltd | Mining & quarrying | 2018 |
| P a Carney Consulting Ltd | Professional & scientific | 2013 |
| P a Joinery and Building Contractors Limited | Construction | 2014 |
| P C I International Limited | Manufacturing | 2003 |
| P D Optics Limited | Manufacturing | 2012 |
| P D Williams Builders Ltd | Construction | 2019 |
| P J M Business Solutions Ltd | Administrative & support | 2020 |
| P James Building Contractors Limited | Construction | 2018 |
| P R H Cost Management Limited | Administrative & support | 2013 |
| P Rawcliffe Limited | Other services | 2006 |
| P Whalley Landscapes Ltd | Administrative & support | 2026 |
| P&G Photography Ltd | Professional & scientific | 2021 |
| P. Hall Electrical Services (NW) Limited | Construction | 2012 |
| P. Rimmer Roofing Services Ltd | Construction | 2020 |
| P.A. Wright & SON Limited | Construction | 2006 |
| P.Kaca Limited | Other services | 2025 |