| Optimaclean Services Ltd | Administrative & support | 2025 |
| Optimal Sourcing Limited | Administrative & support | 2024 |
| Optimise Heating Solutions Ltd | Construction | 2021 |
| Optimised IT Admin Limited | Professional & scientific | 2026 |
| Optimized Academy Ltd | Education | 2025 |
| Optimized Body & Mind Limited | Health & social care | 2019 |
| Optimized Health Ltd | Health & social care | 2022 |
| Optimum Accounting Services Ltd | Professional & scientific | 2022 |
| Optimum Care Occupational Therapy Services. Ltd | Health & social care | 2023 |
| Optimum IT Consulting Limited | Information & communication | 2024 |
| Optimum Response Care Ltd | Health & social care | 2019 |
| Optiqo AI Ltd | Administrative & support | 2025 |
| Opulence Accommodation Ltd | Real estate | 2024 |
| Opulence Executive Chauffeurs Ltd | Transport & logistics | 2019 |
| Opulent Group Intl Ltd | Administrative & support | 2025 |
| Opulent Prestige Bodywork Ltd | Wholesale & retail | 2026 |
| Opulent Prestige Ltd | Transport & logistics | 2022 |
| Opulent Property Solutions Ltd | Real estate | 2021 |
| Oraapharma Ltd | Wholesale & retail | 2020 |
| Oradea Grocery Ltd | Wholesale & retail | 2025 |
| Orakexpress Ltd | Transport & logistics | 2025 |
| Oralieve UK Ltd | Wholesale & retail | 2019 |
| Orange Line Taxi Ltd | Transport & logistics | 2022 |
| Orange Logistics Ltd | Transport & logistics | 2025 |
| Orangebrick Software Consultancy Limited | Information & communication | 2016 |
| Orantion Limited | Information & communication | 2026 |
| ORB Housing Group Ltd | Real estate | 2021 |
| Orbetta Designs Limited | Professional & scientific | 2018 |
| Orbit Air Ltd | Wholesale & retail | 2025 |
| Orbit Legal Consultancy Limited | Professional & scientific | 2022 |
| Orbital Trampoline Park ( Luton ) Limited | Arts & recreation | 2017 |
| Orbitsquare Ltd | Wholesale & retail | 2025 |
| Orbs Construction Ltd | Construction | 2019 |
| Orbutu Ltd | Construction | 2021 |
| Orca Transports Ltd | Transport & logistics | 2024 |
| Orchard Bond Finance PLC | Financial services | 2010 |
| Orchard Finance Limited | Financial services | 2009 |
| Orchard Funding Group PLC | Financial services | 2015 |
| Orchard Funding Limited | Financial services | 2008 |
| Orchard Hill Developments Ltd | Construction | 2023 |
| Orchard Living Group Limited | Real estate | 2026 |
| Orchid Rock Ltd | Wholesale & retail | 2021 |
| Ordame Ltd | Information & communication | 2025 |
| Oree UK Ltd | Wholesale & retail | 2024 |
| Oreee Ltd | Wholesale & retail | 2026 |
| Oreks Developments Limited | Real estate | 2017 |
| Oreks Group Limited | Financial services | 2020 |
| Oreks International Limited | Professional & scientific | 2017 |
| Oreks Investments Limited | Financial services | 2021 |
| Orenzo Trading Ltd | Administrative & support | 2010 |
| Organic Baby Essentials Ltd | Wholesale & retail | 2025 |
| Organic Route Ltd | Wholesale & retail | 2022 |
| Orhancy Limited | Wholesale & retail | 2023 |
| Orial Health Partners Limited | Health & social care | 2022 |
| Orichalcum Industries LLP | | 2024 |
| Orie Mart Limited | Wholesale & retail | 2024 |
| Oriental Express Oxford Ltd | Hospitality | 2020 |
| Origin Access Ltd | Construction | 2017 |
| Origin Education Centre Ltd | Education | 2026 |
| Original Auto Restorations Limited | Manufacturing | 2015 |
| Original Baba LAL Ltd | Hospitality | 2024 |
| Original Garam Masala Limited | Hospitality | 2022 |
| Original Karahi Roti Junction Ltd | Hospitality | 2015 |
| Original Perfect Fried Chicken Limited | Hospitality | 2025 |
| Original Roti Junction Ltd | Hospitality | 2025 |
| Originrise Ltd | Wholesale & retail | 2026 |
| Oriley Pearce Recruitment Limited | Administrative & support | 2025 |
| Orion Global Skills Ltd | Administrative & support | 2026 |
| Orit Marketing Ltd | Professional & scientific | 2026 |
| Orocore Limited | Information & communication | 2025 |
| Orphanguard | Other services | 2024 |
| Orpheus Holdings Ltd | Financial services | 2025 |
| Orynex Ltd | Wholesale & retail | 2026 |
| Osagyefo Consults Ltd | Arts & recreation | 2024 |
| Osaje Services Limited | Public administration | 2023 |
| Osama Asad Ltd | Wholesale & retail | 2024 |
| Osamo Limited | Wholesale & retail | 2025 |
| Osazsworld Limited | Other services | 2017 |
| Osbourne Bingham Ltd | Professional & scientific | 2015 |
| Oscar Incorporated Limited | Education | 2024 |
| Oscar Midco Limited | Financial services | 2019 |
| Oscar Newco Limited | Financial services | 2026 |
| Oscar Topco Limited | Financial services | 2019 |
| Oscarmen Ltd | Transport & logistics | 2025 |
| Oseghele Limited | Health & social care | 2016 |
| Osei-Owusu Limited | Health & social care | 2019 |
| OSL Groundworks Limited | Administrative & support | 2018 |
| OSM Events Consultancy Ltd | Professional & scientific | 2025 |
| Osmond Professional Services Ltd | Health & social care | 2025 |
| Osrj Investments Limited | Professional & scientific | 2024 |
| Osrj Properties Management Limited | Real estate | 2025 |
| Osrob Investment Ltd | Administrative & support | 2019 |
| OSS Holdings Limited | Mining & quarrying | 2012 |
| Ossa Nutritional House Private Ltd | Hospitality | 2026 |
| Ostafie Ltd | Transport & logistics | 2025 |
| Ostrich Limited | Wholesale & retail | 2025 |
| Osullivan Lowe Properties Limited | Construction | 2025 |
| OSZ Engineering Limited | Construction | 2018 |
| Otez Impex Ltd | Transport & logistics | 2025 |
| Otiro I.T. Limited | Information & communication | 2026 |