| One Embargo Limited | Information & communication | 2026 |
| One World A.S Club Ltd | Education | 2023 |
| Onechess Limited | Agriculture & fishing | 2015 |
| Onesource IT Solutions Limited | Information & communication | 2011 |
| Onisoft Consulting Limited | Information & communication | 2016 |
| Only the Brave Group Limited | Administrative & support | 2020 |
| Onodi Investments Limited | Construction | 2020 |
| Onomsky Entertainment Ltd | Arts & recreation | 2021 |
| ONU Services Limited | Agriculture & fishing | 2018 |
| Onyx Consultation & Services Ltd | Information & communication | 2024 |
| Onyx Crane Services Limited | Construction | 2017 |
| Onyx Global Investments Ltd | Real estate | 2015 |
| Onyx Import& Export Ltd | Wholesale & retail | 2019 |
| Onyx Stonework & Restoration Limited | Construction | 2019 |
| OO Group Ltd | Real estate | 2025 |
| Opal Accountancy Ltd | Professional & scientific | 2022 |
| Open Data Consultancy Ltd | Information & communication | 2024 |
| Ophely Co., Ltd | Wholesale & retail | 2021 |
| Opti Heat Ltd | Construction | 2023 |
| Optima EAE Residents Association Limited | Real estate | 2013 |
| Optimisy Solutions Limited | Information & communication | 2015 |
| Optimum Homecare Services Ltd | Health & social care | 2014 |
| Optimus Docs Limited | Health & social care | 2014 |
| Options Healthcare Limited | Health & social care | 2015 |
| Optionsst Limited | Wholesale & retail | 2016 |
| Optivon Ltd | Information & communication | 2026 |
| Opulent Living Management Ltd. | Hospitality | 2019 |
| Opulentis Ltd | Administrative & support | 2025 |
| Opus Development Group Ltd | Financial services | 2018 |
| Opus Development Ltd | Professional & scientific | 2017 |
| Opus Home Working Solutions Ltd | Construction | 2019 |
| Oracle Asset Group Ltd | Extraterritorial | 2016 |
| Orange Enterprises Limited | Real estate | 2003 |
| Orange TIP Limited | Construction | 2019 |
| Orasci Limited | Manufacturing | 2026 |
| Orbit Construction Ltd | Construction | 2022 |
| Orbit Property Developments Ltd | Construction | 2026 |
| Orbital Construction Services Ltd | Construction | 2006 |
| Orbital Property Investments Ltd | Real estate | 2020 |
| Orbro Ltd | Information & communication | 2017 |
| Orchard Green Residents Association Ltd | Households | 2019 |
| Orchestrate Media Limited | Information & communication | 2014 |
| Order & Go Ltd | Hospitality | 2024 |
| Orient 360 Limited | Professional & scientific | 2024 |
| Orient GAS Engineers Ltd | Construction | 2023 |
| Oriental Recruitment Ltd | Administrative & support | 2022 |
| Original Cobblers Limited | Other services | 2014 |
| Orion Transgroup Ltd | Construction | 2023 |
| ORM Autos Ltd | Wholesale & retail | 2014 |
| Orpington Audi & Nissan Ltd. | Wholesale & retail | 2015 |
| Orpington Cafe Ltd | Hospitality | 2020 |
| Orpington Chiropody & Podiatry Limited | Health & social care | 2012 |
| Orpington Crispy COD Ltd | Real estate | 2016 |
| Orpington Endoscopy Solutions Limited | Health & social care | 2018 |
| Orpington Estates Limited | Real estate | 2004 |
| Orpington Eyecare Centre Ltd | Other services | 2016 |
| Orpington First Limited | Other services | 2012 |
| Orpington Foods Ltd | Hospitality | 2025 |
| Orpington Home Rentals Ltd | Real estate | 2022 |
| Orpington Kebab Express Limited | Hospitality | 2026 |
| Orpington Motorworks Ltd | Wholesale & retail | 2024 |
| Orpington Personal Trainers Limited | Health & social care | 2025 |
| Orpington Physiotherapy Limited | Health & social care | 2015 |
| Orpington Plumbing Supplies Limited | Wholesale & retail | 2006 |
| Orpington Rovers Football Club Limited | Arts & recreation | 1984 |
| Orpington Shop Limited | Wholesale & retail | 2025 |
| Orpington Spice Ltd | Hospitality | 2025 |
| Orpington Takeaway Ltd | Hospitality | 2016 |
| Orpington Town Football Club Limited | Arts & recreation | 2025 |
| Orpington Trade Shop Ltd | Wholesale & retail | 2025 |
| Orpinton Express Ltd | Wholesale & retail | 2025 |
| Orsfst Limited | Wholesale & retail | 2025 |
| Ortega Importaciones Ltd | Wholesale & retail | 2025 |
| Ortega Properties Limited | Real estate | 2026 |
| Ortus Fire Construction Ltd | Public administration | 2021 |
| Oryx Advisers Ltd | Professional & scientific | 2018 |
| Osab Catering Ltd | Hospitality | 2025 |
| OSC Jewellers Ltd | Wholesale & retail | 2025 |
| OSJ Ventures Limited | Administrative & support | 2017 |
| Osman & Tomkinson Investments Limited | Real estate | 2018 |
| Osvsm IT Solutions Limited | Information & communication | 2018 |
| Otazo Ltd | Real estate | 2023 |
| Oteso Consulting Ltd | Information & communication | 2021 |
| Oteso Ltd. | Real estate | 2020 |
| Oulton ESG Ltd | Information & communication | 2006 |
| OUR Lady's Pre-School Ltd | Education | 2011 |
| OUR Window Cleaner Ltd | Administrative & support | 2025 |
| Outdoor Logistics Digital Ltd | Construction | 2018 |
| Outdoor Logistics Holdings Limited | Financial services | 2019 |
| Outdoor Logistics UK Ltd. | Construction | 2012 |
| Outline Group Limited | Administrative & support | 2018 |
| Outoftheboxes Limited | Education | 2023 |
| Outsim Limited | Information & communication | 2006 |
| Outsource-Engage Ltd | Professional & scientific | 2025 |
| Ovationdata Group Holdings Limited | Professional & scientific | 2001 |
| Ovationdata Limited | Information & communication | 1986 |
| Oven Glows Ltd | Administrative & support | 2025 |
| Overbury Court (Beckenham) Management Company Limited | Households | 2010 |
| Overleaf Publishers Ltd | Information & communication | 2024 |
| OW Pharma Ltd | Wholesale & retail | 2022 |