| Octavian Media Limited | Professional & scientific | 2023 |
| Octavius Property Management Ltd | Real estate | 2023 |
| Octinet Limited | Real estate | 2010 |
| October Property Ltd | Real estate | 2023 |
| October Textiles Limited | Manufacturing | 2005 |
| Octopus Intelligence Limited | Professional & scientific | 2017 |
| Octopus Lifestar Ltd | Transport & logistics | 2019 |
| Octsris Limited | Financial services | 2023 |
| Oculis Lawyers Ltd | Professional & scientific | 2018 |
| Oculocare Ltd | Administrative & support | 2020 |
| Oculus Wealth Management (Nottinghamshire) Limited | Financial services | 2022 |
| Oculuxe Ltd | Wholesale & retail | 2020 |
| Odalaja Limited | Health & social care | 2015 |
| Odara Management Consultancy Ltd | Professional & scientific | 2018 |
| Oddauthor Limited | Professional & scientific | 2007 |
| Oddie Dalton & Company Limited | Financial services | 1973 |
| Odei Consult Limited | Health & social care | 2025 |
| Odikk Services (UK) Ltd | Transport & logistics | 2021 |
| ODJ Solutions Limited | Professional & scientific | 2025 |
| Odofina Ltd | Health & social care | 2024 |
| Odogwu Kitchen Ltd | Hospitality | 2026 |
| Odoproperties Ltd | Real estate | 2023 |
| ODU Miracle Special Ltd | Health & social care | 2020 |
| OE Investments Ltd | Financial services | 2022 |
| OEO Ventures Ltd | Financial services | 2024 |
| OEX Limited | Professional & scientific | 2026 |
| OFF Limits Ltd | Arts & recreation | 2004 |
| OFF Script Consulting Ltd | Professional & scientific | 2025 |
| OFF the Line Coaching Ltd | Professional & scientific | 2025 |
| Off-Road Trucks Limited | Professional & scientific | 2013 |
| Offeryn Software Ltd | Information & communication | 2026 |
| Offgrid Coaching Ltd | Health & social care | 2022 |
| Office Furniture 2000 (UK) Limited | Wholesale & retail | 2003 |
| Office Gear Limited | Wholesale & retail | 2000 |
| Officepro Direct Ltd | Wholesale & retail | 2012 |
| Official Emerald Cards Ltd | Wholesale & retail | 2025 |
| Offispace Ltd | Real estate | 2025 |
| Offline Investments Ltd | Real estate | 2024 |
| Offlovin Ltd | Information & communication | 2025 |
| Offset Press (Long Eaton) Limited | Real estate | 1924 |
| Offshore Project Consultants Ltd | Professional & scientific | 2022 |
| Offsite Business Support Ltd | Administrative & support | 2025 |
| OG Boots Building Co Ltd | Hospitality | 2025 |
| OG Nera Ltd | Information & communication | 2025 |
| OGA Mart Ltd | Wholesale & retail | 2025 |
| Ogando School of Dance Limited | Arts & recreation | 2003 |
| Ogelicious Healthcare Limited | Health & social care | 2020 |
| OGO Property Ltd | Real estate | 2025 |
| Ogston Sailing Club Limited | Arts & recreation | 2025 |
| OGX Holdings Limited | Real estate | 2025 |
| OH Camera Solutions Limited | Information & communication | 2022 |
| OH Construction Services Limited | Construction | 2023 |
| OH Management Solutions Limited | Health & social care | 2017 |
| OH SO Creamy Ltd | Hospitality | 2025 |
| OH SO Pretty Cleaning Services Ltd | Administrative & support | 2022 |
| Ohana 2025 Group Ltd | Professional & scientific | 2025 |
| Ohannes Limited | Wholesale & retail | 2020 |
| Ohbagoo Limited | Wholesale & retail | 2012 |
| Ohemaa Sales Connect Limited | Wholesale & retail | 2025 |
| OHM Check Limited | Construction | 2016 |
| OHM Electrical Contractors Limited | Construction | 2017 |
| Ohne Limited | Wholesale & retail | 2017 |
| Oikos Estate Agency Ltd | Real estate | 2022 |
| Oikos Holdings Ltd | Real estate | 2021 |
| Oisuta Limited | Extraterritorial | 2007 |
| OJ Steakhouse Ltd | Hospitality | 2024 |
| OJA Foods Ltd | Wholesale & retail | 2022 |
| Ojas Local Limited | Wholesale & retail | 2020 |
| OJB Property Services Ltd | Real estate | 2024 |
| Okaeri WIN Ltd | Real estate | 2022 |
| OKE Properties Ltd | Real estate | 2024 |
| Okende Bakery Limited | Manufacturing | 2023 |
| Okende Coffee Limited | Hospitality | 2018 |
| Okig Global Resources Limited | Professional & scientific | 2025 |
| Okrafo-Smart Architects Limited | Professional & scientific | 2016 |
| OKS Multi Services Ltd | Transport & logistics | 2026 |
| Okyloki Limited | Wholesale & retail | 2014 |
| Olaf Trans Ltd | Transport & logistics | 2024 |
| Olaj Homes Ltd | Real estate | 2024 |
| Olam Developments Limited | Construction | 2021 |
| Olam Real Estate Limited | Real estate | 2021 |
| Olando Foods Limited | Wholesale & retail | 2025 |
| Olanthe Ltd | Information & communication | 2021 |
| Olariu Transport Ltd | Transport & logistics | 2016 |
| Old Bank Mapperley Limited | Hospitality | 2021 |
| Old Basford School | Education | 2012 |
| Old English Doors Limited | Manufacturing | 2022 |
| Old Hall Landscapes Limited | Extraterritorial | 2004 |
| Old Hall Nurseries Limited | Wholesale & retail | 1988 |
| Old Nepal Limited | Information & communication | 2022 |
| Old School House Nursery Limited | Education | 1990 |
| Old Soil Property Group Limited | Real estate | 2020 |
| Old Town Barbershop NG9 Ltd | Other services | 2024 |
| Old World Craft Ltd | Wholesale & retail | 2025 |
| Oldan Padel Ltd | Manufacturing | 2023 |
| Olde English Chippy Limited | Hospitality | 2005 |
| Oldham Court Freehold Limited | Households | 2012 |
| Oldnall Fewster Construction Ltd | Construction | 2023 |
| Oldro EPC Ltd. | Administrative & support | 2021 |
| Oldro Ltd. | Real estate | 2017 |