| Opulent Enterprise Ltd | Wholesale & retail | 2025 |
| Opulent Hair Limited | Other services | 2021 |
| Opulent Home Renovations Ltd | Construction | 2024 |
| Oracle Projects Ltd | Real estate | 2026 |
| Oral 24 Ltd | Health & social care | 2025 |
| Orama Contracts Ltd | Other services | 2025 |
| Orange Glasses Limited | Real estate | 2015 |
| Orange Impct Limited | Real estate | 2025 |
| Orange Key Investments Ltd | Real estate | 2017 |
| Orange Keys Developments Limited | Real estate | 2024 |
| Orange Skip Limited | Water & waste | 2018 |
| Orangegold Ltd | Health & social care | 2021 |
| Orbert Aesthetics Limited | Health & social care | 2022 |
| Orbexo Ltd | Wholesale & retail | 2024 |
| Orbit Food Ltd | Wholesale & retail | 2016 |
| Orbit UK Import & Export Ltd | Wholesale & retail | 2024 |
| Orbit UK International Ltd | Wholesale & retail | 2026 |
| Orbit Visa Ltd | Hospitality | 2026 |
| Orbital Community Housing Ltd | Real estate | 2019 |
| Orbix Investment Ltd | Real estate | 2026 |
| Orca Training Limited | Education | 2010 |
| Orchard Property Care Ltd | Extraterritorial | 2018 |
| Orchard Traders Ltd | Wholesale & retail | 2026 |
| Orchid Cellmark Ltd | Professional & scientific | 2000 |
| Orchid Invest Limited | Real estate | 2023 |
| Orchid Living Ltd | Health & social care | 2024 |
| Orcinus Limited | Professional & scientific | 2016 |
| Ordian Limited | Real estate | 1998 |
| Ordovia Limited | Real estate | 2024 |
| Orel Management Limited | Hospitality | 2015 |
| Oreo Management Services Ltd | Construction | 2023 |
| Oreris Ltd | Transport & logistics | 2019 |
| Oreum Network Ltd | Information & communication | 2026 |
| Organic Rank Pro Ltd | Information & communication | 2025 |
| Orient Hill Limited | Hospitality | 2020 |
| Oriental Deli Food Ltd | Hospitality | 2024 |
| Oriental Wellbeing & Beauty Ltd | Other services | 2018 |
| Original Vitality Ltd | Wholesale & retail | 2018 |
| Origions Ltd | Wholesale & retail | 2018 |
| Orinmore Technology Ltd | Information & communication | 2026 |
| Orinox Ltd | Information & communication | 2026 |
| Orivano Ltd | Wholesale & retail | 2026 |
| Orlando Holdings Limited | Financial services | 2025 |
| ORLIN15 Ltd | Wholesale & retail | 2026 |
| ORM Futures Limited | Real estate | 2025 |
| Orme Consultancy Limited | Construction | 2024 |
| ORO Real Estate Limited | Real estate | 2026 |
| Orsi Cleaning Ltd | Households | 2025 |
| Orson Equipment Limited | Extraterritorial | 1998 |
| Orstone LLP | | 2013 |
| Orthelo Properties Ltd | Real estate | 2025 |
| Ortho-Med (Supplies) Limited | Wholesale & retail | 1992 |
| Ortho-Uk Limited | Extraterritorial | 2009 |
| Orvanta Limited | Wholesale & retail | 2025 |
| Orvello Ltd | Wholesale & retail | 2026 |
| Oryx 360 Ltd | Wholesale & retail | 2026 |
| OS Labels, Ltd. | Information & communication | 2023 |
| Osaghae Nosakhare Limited | Health & social care | 2020 |
| Osaif Private Ltd | Wholesale & retail | 2025 |
| OSAKA66 Limited | Hospitality | 2024 |
| Osato Automobile and Logistics Ltd | Wholesale & retail | 2025 |
| Oscroft & Co Limited | Professional & scientific | 2008 |
| OSG Service Group Ltd | Administrative & support | 2020 |
| Oshiniconstruction Ltd | Construction | 2025 |
| Oshocontinental UK Limited | Health & social care | 2017 |
| Osis&Vera Ltd | Transport & logistics | 2021 |
| OSK Khattra Ltd | Transport & logistics | 2022 |
| OSM Services Ltd | Manufacturing | 2018 |
| Osman Bakery Ltd | Wholesale & retail | 2025 |
| Osprey Inns Limited | Extraterritorial | 2002 |
| OSS Developments Ltd | Real estate | 2020 |
| OSS Investments Limited | Real estate | 2025 |
| Ostr 3D Ltd | Professional & scientific | 2025 |
| Osujic Ltd | Construction | 2014 |
| Oswestry Industrial Buildings Limited | Real estate | 1979 |
| Otala Limited | Administrative & support | 2019 |
| Otche & Labs Tapers Ltd | Construction | 2017 |
| Oteq Consulting Ltd | Information & communication | 2025 |
| Otsmith Limited | Transport & logistics | 2025 |
| Otterbourne Court Ltd | Households | 2019 |
| Otto Renewables Limited | Administrative & support | 2023 |
| Oudewater Invest Ltd | Real estate | 2026 |
| OUR Bold Earth Ltd | Manufacturing | 2020 |
| Ourdigitizer Ltd | Professional & scientific | 2026 |
| Ourfoodandskin Limited | Hospitality | 2020 |
| Ourithreads Ltd | Wholesale & retail | 2026 |
| Outcome Care and Support Limited | Health & social care | 2015 |
| Outside Edge Ltd | Professional & scientific | 2023 |
| Ouzo Limited | Hospitality | 2019 |
| OV Media Limited | Information & communication | 2012 |
| Ovako Limited | Administrative & support | 1999 |
| Oval (1703) Limited | Real estate | 2002 |
| Ovalglen Limited | Transport & logistics | 2018 |
| Over the Moon Campers Ltd | Administrative & support | 2007 |
| Overall Services Limited | Administrative & support | 2023 |
| Overdevest Real Estate Ltd | Real estate | 2026 |
| Overtime 22 Ltd | Professional & scientific | 2025 |
| Overtime AGC Ltd | Professional & scientific | 2024 |
| Overview 2000 Computing Limited | Information & communication | 1989 |
| Overwatch Aerospace Ltd | Manufacturing | 2020 |