| Orangebox Holdings Limited | Education | 2022 |
| Orangebox Training Solutions Limited | Education | 2016 |
| Orangebox Training Solutions UK Limited | Education | 2009 |
| Oranje Ltd | Construction | 2014 |
| Oraton Advisory Limited | Financial services | 2021 |
| ORB Property Ltd | Real estate | 2020 |
| Orbify Retail Limited | Wholesale & retail | 2025 |
| Orbital Comfy Stays Ltd | Real estate | 2023 |
| Orbital Cyber Security Limited | Information & communication | 2025 |
| Orbital Holdings Limited | Professional & scientific | 2003 |
| Orbital Recruitment (Yorkshire) Limited | Administrative & support | 2006 |
| Orbital Recruitment Group Limited | Financial services | 2023 |
| Orbital Recruitment Limited | Administrative & support | 2001 |
| Orbitec Ltd | Manufacturing | 2004 |
| Orbitech Limited | Administrative & support | 2017 |
| Orchard Barn Designs Ltd | Agriculture & fishing | 2022 |
| Orchard Barns Limited | Education | 2019 |
| Orchard Farm Poultry Ltd | Agriculture & fishing | 2025 |
| Orchard Green Residents (Westhoughton) Management Company Limited | Households | 2008 |
| Orchard Mill Estate Management Company Limited | Households | 2023 |
| Orchard Park Residents Management Company Limited | Households | 2021 |
| Orchard Private Day Nurseries Limited | Education | 1999 |
| Orchard Property & Financial Services Limited | Financial services | 1997 |
| Orchard School Limited | Extraterritorial | 2005 |
| Orchard School Properties Limited | Extraterritorial | 2005 |
| Orchard Trailers Holdings Limited | Financial services | 2021 |
| Orchard Trailers Limited | Professional & scientific | 2017 |
| Orchard Works Joinery Limited | Construction | 2003 |
| Orchid Gold Ltd | Professional & scientific | 2013 |
| Orchid Thai Massage Derby Limited | Other services | 2025 |
| Orcus Limited | Information & communication | 1993 |
| Orderly Holdings Limited | Financial services | 2024 |
| Orderly Limited | Information & communication | 2008 |
| Ordgarth Ltd | Other services | 2025 |
| Orebus Consulting Ltd | Information & communication | 2018 |
| Oregateway Limited | Other services | 2024 |
| Orege UK Limited | Manufacturing | 2016 |
| Oreillyengineering Limited | Construction | 2025 |
| Organisation Change Solutions Limited | Professional & scientific | 2010 |
| Orid Medicals Limited | Health & social care | 2025 |
| Oriental HO Limited | Hospitality | 2024 |
| Oriental Navigator (UK) Limited | Education | 2000 |
| Oriental Tastea Ltd | Hospitality | 2018 |
| Oriental Threads Ltd | Wholesale & retail | 2024 |
| Origin Group Limited | Construction | 2015 |
| Origin UK Energy Services Limited | Construction | 2013 |
| Original Estates Ltd | Real estate | 2024 |
| Original Midnight Limited | Information & communication | 2025 |
| Orion Invests Ltd | Real estate | 2025 |
| Orissa Premier Dining Ltd | Hospitality | 2021 |
| Orkestrate Group Limited | Professional & scientific | 2024 |
| Orlando Healthcare Limited | Wholesale & retail | 2024 |
| Orrery Theatre Ltd | Arts & recreation | 2022 |
| Orridge & Dunn Ltd | Financial services | 2011 |
| Orsam Trailers Limited | Administrative & support | 2014 |
| Orsus Group Limited | Wholesale & retail | 2021 |
| Orthocorrect Ltd | Health & social care | 2017 |
| Orthopaedic VET Limited | Professional & scientific | 2021 |
| Oryxel Group Ltd | Arts & recreation | 2025 |
| Osborne Brookside Road Limited | Households | 2022 |
| Oscar Blue Limited | Wholesale & retail | 2025 |
| Osifproperties Ltd | Real estate | 2022 |
| Osintera Ltd | Information & communication | 2026 |
| Osjg Holdings Limited | Real estate | 2023 |
| Oskar Cafe Ltd | Hospitality | 2025 |
| Oskz Property Ltd | Real estate | 2026 |
| Oslek Coatings Limited | Manufacturing | 2025 |
| OSM Bungalow Ltd | Real estate | 2023 |
| Osmaston Business Park Limited | Administrative & support | 2010 |
| Osmaston Day Nursery Limited | Health & social care | 2023 |
| Osmaston Mini Market Limited | Wholesale & retail | 2025 |
| Osmaston Park Community Centre Community Interest Company | Other services | 2008 |
| Osmaston Road Store Limited | Wholesale & retail | 2026 |
| Osprey & Partners Limited | Professional & scientific | 2023 |
| Osprey Mechanical Services Ltd | Construction | 2014 |
| Osprey Property Investment Ltd | Construction | 2021 |
| Ossie Ardiles Sport Limited | Arts & recreation | 2013 |
| Ostad Enterprises Ltd | Financial services | 2025 |
| Osteopathy Derby Limited | Health & social care | 2010 |
| Ostrichsized Ltd | Professional & scientific | 2008 |
| Osutin Limited | Professional & scientific | 2015 |
| OT Direct Limited | Health & social care | 2003 |
| OT Matters Ltd | Health & social care | 2020 |
| Otaku World & Otaku World Clothing Limited | Wholesale & retail | 2022 |
| Otbsports Ltd | Information & communication | 2026 |
| Otium Design & Build Ltd | Construction | 2017 |
| OTS Advanced Properties Limited | Real estate | 2025 |
| Otterbrook Developments Ltd. | Financial services | 2018 |
| Ottie and Tottie Limited | Wholesale & retail | 2018 |
| Ouassini Ltd | Health & social care | 2015 |
| OUD Royale Limited | Wholesale & retail | 2025 |
| Ouns Group of Companies Ltd | Wholesale & retail | 2026 |
| OUR First Days Limited | Information & communication | 2025 |
| OUR Mickleover Community Interest Company | Extraterritorial | 2018 |
| OUR Stable Limited | Administrative & support | 2023 |
| Ourovia Advisory Ltd | Professional & scientific | 2025 |
| OURPRODUCTS4U Ltd | Wholesale & retail | 2024 |
| Ourstory Community Hub CIC | Administrative & support | 2026 |
| OUT the Bubble Design Limited | Professional & scientific | 2011 |
| Outerange Limited | Construction | 2000 |