| OJ Investments Limited | Extraterritorial | 2016 |
| OJR Outdoor Services Ltd | Administrative & support | 2024 |
| OK Labels & Packaging Limited | Wholesale & retail | 2015 |
| Okrasa. Ltd | Transport & logistics | 2015 |
| Olaf & Olek Ltd. | Transport & logistics | 2021 |
| Oldham Broadway Developments Limited | Real estate | 1995 |
| Oliva Pizzas Limited | Hospitality | 2019 |
| Ollie Gill Colour Ltd | Professional & scientific | 2021 |
| OLM Tech Ltd | Wholesale & retail | 2024 |
| Olmack Limited Ltd | Construction | 2017 |
| Olowe & Co Ltd | Hospitality | 2017 |
| Olympus Foods Ltd | Hospitality | 2026 |
| OM Sharkarte Studio Ltd | Arts & recreation | 2024 |
| Omda Tutoring Ltd | Education | 2026 |
| Omega Distribution Services Limited | Transport & logistics | 2026 |
| Omnia Asset Finance Limited | Financial services | 2018 |
| Omnia Capital Limited | Financial services | 2018 |
| Omnia Property Finance Limited | Financial services | 2018 |
| Omonebos Ltd | Health & social care | 2017 |
| ON Divorce Limited | Financial services | 2025 |
| ON Point Pet Supplies Ltd | Wholesale & retail | 2021 |
| ON the Rivet Limited | Arts & recreation | 2013 |
| One by One Care Ltd | Health & social care | 2021 |
| One Hundred Ways Bars Limited | Hospitality | 2026 |
| One Less Thing (Holdings) Limited | Professional & scientific | 2021 |
| One Less Thing (Operations) Limited | Administrative & support | 2023 |
| One Less Thing Limited | Administrative & support | 2023 |
| One Stop Autos (Cheshire) Ltd | Wholesale & retail | 2012 |
| One Stop Design and Construct Limited | Professional & scientific | 2004 |
| One Stop Fireworks Ltd | Other services | 2020 |
| One Stop Hire Limited | Administrative & support | 2003 |
| One Stop Power Rental Limited | Wholesale & retail | 2014 |
| One Stop Sweet Shop Ltd | Wholesale & retail | 2020 |
| One Vision GRP Ltd | Manufacturing | 2023 |
| One Web Solutions Ltd | Wholesale & retail | 2019 |
| One Wing Transport Limited | Transport & logistics | 2014 |
| Onecall Group Ltd | Administrative & support | 2018 |
| Online Sports Group Ltd | Wholesale & retail | 2026 |
| Only Tanz Ltd | Other services | 2022 |
| Onside Sports Education Limited | Education | 2013 |
| Ookin Ltd | Hospitality | 2024 |
| Opal Recruitment Limited | Administrative & support | 2014 |
| Openshaw Group Holdings Limited | Construction | 2020 |
| Optical Directory Limited | Extraterritorial | 2004 |
| Optical Marketplace Limited | Health & social care | 2004 |
| Optima Total Solutions Limited | Information & communication | 2016 |
| Optimum Biomedical Ltd | Professional & scientific | 2019 |
| Optimum Glazing Ltd | Manufacturing | 2019 |
| Optimum Options Limited | Health & social care | 2018 |
| Options Financial Planning Ltd | Professional & scientific | 2021 |
| Optsm Limited | Professional & scientific | 2017 |
| Optulis Ltd | Administrative & support | 2026 |
| Orac Developments Ltd | Real estate | 2021 |
| Orange Property Management Limited | Professional & scientific | 2025 |
| Orchard Gate (Ropley) Management Company Limited | Households | 2018 |
| Orchestra Bind Ltd | Manufacturing | 2025 |
| Ordo Works Limited | Information & communication | 2025 |
| Oregano House Ltd | Hospitality | 2021 |
| Oriental Harmony Wellness Limited | Other services | 2026 |
| Orimi Nails Chorley Ltd | Other services | 2025 |
| Orion Property Holdings Ltd | Real estate | 2020 |
| Orion Technical Event Services Ltd | Other services | 2019 |
| Ormskirks Eats Delivery Limited | Other services | 2026 |
| Ormston Consult Limited | Professional & scientific | 2013 |
| Ormston Consult Training Limited | Professional & scientific | 2016 |
| Orosurgeon Ltd | Professional & scientific | 2017 |
| ORR Holdings Limited | Financial services | 2024 |
| ORR Medical Limited | Health & social care | 2010 |
| Orsa Designs Limited | Professional & scientific | 2025 |
| Orsa Interiors Limited | Professional & scientific | 2023 |
| Oryon X Ltd | Information & communication | 2026 |
| OS Construction (London) Ltd | Construction | 2016 |
| OS NDT Solutions Ltd | Professional & scientific | 2026 |
| OS Projects & Developments Ltd | Construction | 2025 |
| OSCARLOGISTIC88 Ltd | Transport & logistics | 2019 |
| Osiris Health Limited | Health & social care | 2015 |
| Osted Limited | Real estate | 2023 |
| Otgsuk Ltd | Manufacturing | 2023 |
| Otis Sandell Golf Ltd | Arts & recreation | 2025 |
| OTM Valves Ltd | Other services | 2024 |
| OTP Solutions Ltd | Information & communication | 2026 |
| Ourdeals Limited | Wholesale & retail | 2021 |
| OUT2SERVE Environmental Services Ltd | Professional & scientific | 2017 |
| Outback Films Ltd | Professional & scientific | 2016 |
| Outland House Ltd | Wholesale & retail | 2010 |
| Outlaw Marketing Ltd | Information & communication | 2022 |
| Outpost Eco Design Limited | Professional & scientific | 2022 |
| Outpost Hospitality Ltd | Manufacturing | 2024 |
| Outram Building & Restoration Ltd | Construction | 2025 |
| Outreach Opera Collective CIC | Arts & recreation | 2024 |
| Outside Events Ltd | Other services | 2021 |
| Overland Boat Movements Ltd | Transport & logistics | 2013 |
| Ovon Global Ltd | Financial services | 2019 |
| Owsten Ltd | Administrative & support | 2014 |
| OWT Groundworks & Building Ltd | Construction | 2007 |
| Oxford Court Management (Manchester) Limited | Real estate | 1985 |
| Oxford Hotel Services Ltd | Hospitality | 2015 |
| Oxford Street (Chorley) Limited | Real estate | 2021 |
| Oxfreight (UK) Ltd | Transport & logistics | 2020 |
| Ozcip Holdings Limited | Hospitality | 2020 |