| Openstack Business Consulting Ltd | Information & communication | 2025 |
| Opentek Ltd | Information & communication | 2021 |
| Openweigh Ltd | Manufacturing | 2014 |
| Opera & Co Ltd | Professional & scientific | 2012 |
| Opera Synergy CYF. | Arts & recreation | 2023 |
| Operation Moonlight Limited | Arts & recreation | 2025 |
| Operation-Fitnessgym Ltd | Arts & recreation | 2019 |
| Operations and Management 1 Ltd | Administrative & support | 2019 |
| Opeuristic | Administrative & support | 2019 |
| Opexis Ltd | Information & communication | 2026 |
| OPH Events Limited | Hospitality | 2007 |
| OPH Hospitality Limited | Hospitality | 2015 |
| Ophion Group Ltd | Administrative & support | 2017 |
| Ophir Group Ltd | Financial services | 2018 |
| Ophira Ventures Limited | Wholesale & retail | 2025 |
| Ophirton Property Company Limited | Real estate | 2019 |
| Opibus Corporation Limited | Wholesale & retail | 2019 |
| Opicraft Ltd | Wholesale & retail | 2025 |
| Opifer Investments Limited | Financial services | 2014 |
| Opimus INT Ltd | Financial services | 2019 |
| Opis Group Limited | Information & communication | 2021 |
| Opland Business PC | | 2019 |
| OPM Capital Limited | Wholesale & retail | 2020 |
| Opodo Deal Centre Limited | Administrative & support | 2025 |
| Opodo Flight Centre Limited | Administrative & support | 2025 |
| Opodo Flight Deals Limited | Administrative & support | 2025 |
| Opodo FLY Hub Limited | Administrative & support | 2025 |
| Opodo FLY Limited | Administrative & support | 2025 |
| Opodo Gateway Limited | Administrative & support | 2025 |
| Opodo Holidays Limited | Professional & scientific | 2025 |
| Opodo Tour Limited | Professional & scientific | 2025 |
| Opodo Travels Limited | Administrative & support | 2025 |
| Opodo Trips Limited | Administrative & support | 2025 |
| OPP Project Services Limited | Professional & scientific | 2015 |
| Oppa Chicken Ltd | Hospitality | 2023 |
| Oppo Solution Services Limited | Administrative & support | 2019 |
| Opra Avanti Ltd | Administrative & support | 2009 |
| Oprelay Technical Support Services Limited | Information & communication | 2018 |
| Oprema Limited | Wholesale & retail | 2010 |
| Opsfactory Limited | Information & communication | 2007 |
| Opsia Communications Limited | Information & communication | 2016 |
| Opsys Ltd | Manufacturing | 2018 |
| Optec Services Ltd | Information & communication | 2019 |
| Opti Protocol Limited | Professional & scientific | 2018 |
| Opticall Healthcare Limited | Health & social care | 2001 |
| Optiestimates Ltd | Construction | 2025 |
| Optigenix Technologies Ltd | Information & communication | 2024 |
| Optilan Group Limited | Professional & scientific | 2008 |
| Optilan Holdco 3 Limited | Administrative & support | 2017 |
| Optima Accountants Limited | Professional & scientific | 2015 |
| Optima Building Services Ltd | Construction | 2025 |
| Optima Cura Holdings Ltd | Financial services | 2025 |
| Optima Veterinary Solutions Ltd | Professional & scientific | 2017 |
| Optimal Building and Maintenance Ltd | Construction | 2024 |
| Optimal Chiropractic and Wellness Centre Limited | Health & social care | 2014 |
| Optimal EYE Care Ltd | Health & social care | 2017 |
| Optimalinkholdings Ltd | Information & communication | 2025 |
| Optimapay Limited | Construction | 2020 |
| Optimar One Services Ltd | Professional & scientific | 2018 |
| Optimatch Solutions Limited | Administrative & support | 2026 |
| Optimax Logistics Ltd | Transport & logistics | 2024 |
| Optimera Ltd | Information & communication | 2025 |
| Optimize Chiropractic Ltd | Health & social care | 2024 |
| Optimum Blue Ltd | Wholesale & retail | 2020 |
| Optimum Credit Limited | Financial services | 2020 |
| Optimum DEX Limited | Information & communication | 2025 |
| Optimum Fitness Ltd | Arts & recreation | 2025 |
| Optimum Management (London) Limited | Households | 2015 |
| Optimum Stone Ltd | Construction | 2019 |
| Optimus Seel Street Limited | Real estate | 2022 |
| Optinon Limited | Wholesale & retail | 2025 |
| Optional Remaps Ltd | Manufacturing | 2018 |
| Optiqota Ltd | Transport & logistics | 2024 |
| Optispine Limited | Health & social care | 2008 |
| Optivalue Property Solutions Ltd | Wholesale & retail | 2021 |
| Optom Support Ltd | Administrative & support | 2018 |
| Optrex Properties Limited | Real estate | 2024 |
| Opulence & Serenity Ltd | Other services | 2025 |
| Opulent Agency Ltd | Professional & scientific | 2017 |
| Opulent Nights Ltd | Real estate | 2025 |
| Opulent Reality Limited | Information & communication | 2023 |
| Opulent Wheels Ltd | Wholesale & retail | 2023 |
| Opulentus Ltd | Wholesale & retail | 2022 |
| Opulix Services Ltd | Professional & scientific | 2021 |
| Opus Lounge Limited | Professional & scientific | 2005 |
| Opus Productive Ltd | Arts & recreation | 2024 |
| Opus Revisions & Montage Ltd | Administrative & support | 2024 |
| OPX Software Limited | Information & communication | 2023 |
| Oracle Beauty Limited | Administrative & support | 2012 |
| Oracle Electrics Ltd | Construction | 1998 |
| Oraclet Bracelets Limited | Wholesale & retail | 2025 |
| Oral Health Solutions Limited | Health & social care | 2010 |
| Oral Surgery Solutions Ltd | Health & social care | 2018 |
| Orange and Green Compliance Solutions Limited | Professional & scientific | 2019 |
| Orange Chilli Ltd | Hospitality | 2025 |
| Orange Commercial Finance Ltd | Financial services | 2018 |
| Orange Forest Tree & Landscapes Ltd | Administrative & support | 2022 |
| Orange FOX Solutions Limited | Information & communication | 2021 |
| Orange Llama Developments Ltd | Construction | 2022 |
| Orange Llama Ltd | Construction | 2018 |