| Oakley Homes and Lettings Ltd | Real estate | 2020 |
| Oakley Sales and Lettings Ltd | Real estate | 2024 |
| Oakscroft Construction Limited | Construction | 2024 |
| Oakscroft Group Limited | Transport & logistics | 2025 |
| Oaktree (Kent) Limited | Other services | 2010 |
| Oakview Holiday Park Limited | Hospitality | 2020 |
| Oanjoa NNE Ltd | Wholesale & retail | 2025 |
| OAO Services Ltd | Information & communication | 2026 |
| OB Kent Ltd | Other services | 2020 |
| OB Styles Limited | Professional & scientific | 2025 |
| OBB Group Ltd | Construction | 2024 |
| Obbsurfaces Ltd | Construction | 2023 |
| Objective Perspective Ltd | Information & communication | 2025 |
| Obsidian Media Group Ltd | Professional & scientific | 2026 |
| OCB Holdings Limited | Financial services | 2020 |
| Ocean Counselling Training LLP | | 2012 |
| Ocean Gray KBS Ltd | Construction | 2020 |
| Ocean Land Support Ltd | Other services | 2022 |
| Ocean LOW Cost Counselling Limited | Health & social care | 2026 |
| Ocean Valeting Ltd | Other services | 2019 |
| Ocean View RTM Company Limited | Households | 2023 |
| Ocean View Services BK Limited | Hospitality | 2022 |
| Ocean Warehouse Ltd | Wholesale & retail | 2018 |
| Oceane Company Limited | Health & social care | 2012 |
| Oceanic Eats X Àmàlà Buka Limited | Hospitality | 2024 |
| Oddy Consultancy Limited | Information & communication | 2016 |
| Odis Medical Services Ltd | Health & social care | 2024 |
| OE Recruitment Solutions Limited | Professional & scientific | 2024 |
| Ofuzim Care Ltd | Health & social care | 2025 |
| Ogunbanjo Surveying Services Limited | Construction | 2024 |
| Ohsewa Beauty Empire Limited | Other services | 2025 |
| OJJ Capital Ltd | Real estate | 2020 |
| OJJ FX Ltd | Financial services | 2019 |
| OJJ Property Ltd | Real estate | 2020 |
| Okotie Ltd | Wholesale & retail | 2020 |
| Okun-Inu Limited | Information & communication | 2025 |
| Olady Homes Limited | Real estate | 2023 |
| Olady UK Ltd | Information & communication | 2013 |
| Old 4 Legs Limited | Arts & recreation | 2007 |
| Old Lion Brewery Ltd | Manufacturing | 2025 |
| Oldbury Real Estate Holding Limited | Real estate | 2021 |
| Oldfield Plumbing & Heating Limited | Construction | 2018 |
| Oldsgreen Associates Limited | Manufacturing | 2007 |
| Olio Limited | Construction | 2005 |
| Oliva Trading Ltd | Hospitality | 2017 |
| Olive & Oak Property Development Ltd | Construction | 2024 |
| Olivedog Productions Limited | Arts & recreation | 2017 |
| Olivia Hudson Limited | Professional & scientific | 2020 |
| Olobe Kitchen Ltd | Hospitality | 2020 |
| Olsense Electrical Limited | Construction | 2019 |
| Olsense Limited | Information & communication | 2015 |
| Oluwasegun Ltd | Professional & scientific | 2022 |
| Omas Concept Ltd | Information & communication | 2021 |
| Omega Tutoring Services Limited | Education | 2022 |
| Omfeonix Agritech Ltd | Financial services | 2023 |
| OMG Beverages Limited | Wholesale & retail | 2005 |
| Omjm Trading Limited | Wholesale & retail | 2026 |
| Omni Trading Tools Ltd | Information & communication | 2026 |
| Omorfia by Hayley Ltd | Other services | 2023 |
| ON the GAS Boilercare Limited | Construction | 2025 |
| ONC Limited | Real estate | 2020 |
| One Medic Ltd | Health & social care | 2023 |
| One Stankus Ltd | Real estate | 2024 |
| Online Parts Ltd | Wholesale & retail | 2019 |
| Onlinesikhstore Ltd | Wholesale & retail | 2017 |
| Onosehi Ltd | Other services | 2021 |
| Onyx Therapeutic Services Ltd | Health & social care | 2024 |
| Opalfield Limited | Other services | 2014 |
| OPD Associates Ltd | Real estate | 2021 |
| Opea Limited | Professional & scientific | 2022 |
| Operation Lasertag Ltd | Arts & recreation | 2025 |
| Opeyemi Moradeke Popoola Ltd | Extraterritorial | 2025 |
| Opportunity Care Services Ltd | Health & social care | 2023 |
| Opravale Ltd | Construction | 2021 |
| Optimal Access Scaffolding Ltd | Construction | 2024 |
| Optimal Tech Ltd | Construction | 2019 |
| Optimize Site Solutions Ltd | Construction | 2022 |
| Optimize Storage Limited | Transport & logistics | 2019 |
| Optimized Metal Fabrication Limited | Manufacturing | 2019 |
| Optimum Cabling & Security Specialists Ltd | Construction | 2024 |
| Optimum Electrical Installations Limited | Construction | 2023 |
| Optiquip UK Ltd | Wholesale & retail | 2017 |
| Optjak Limited | Manufacturing | 2019 |
| Opulence Gold Ltd | Hospitality | 2024 |
| Opzing Ltd | Professional & scientific | 2025 |
| Oradent Limited | Health & social care | 2019 |
| Oradent Operations Limited | Health & social care | 2022 |
| Oradent Properties Limited | Real estate | 2018 |
| Oraelhairandbeauty Ltd | Other services | 2025 |
| Oral History Medway CIC | Arts & recreation | 2025 |
| Orange and Black Holdings Ltd | Other services | 2020 |
| Orange Boom Golf Limited | Wholesale & retail | 2025 |
| Orbison (2011) Limited | Financial services | 2011 |
| Orbison Products Limited | Manufacturing | 1985 |
| Orca Marine Ltd | Transport & logistics | 2022 |
| Orchard Administration Ltd | Financial services | 2014 |
| Orchard Glazing Ltd | Administrative & support | 2015 |
| Orchard Plumbing Trustee Limited | Construction | 2024 |
| Orchard Stride Limited | Information & communication | 2019 |
| Orchard View Services Ltd | Construction | 2023 |