| Oakdale Real Estate Ltd | Real estate | 2025 |
| Oakes Real Estate Limited | Administrative & support | 2016 |
| Oakfern Grove Limited | Real estate | 2007 |
| Oakfield Supermarket Limited | Wholesale & retail | 2026 |
| Oakhill Consultations Ltd | Real estate | 2022 |
| Oakhill Garage Sheff Ltd | Wholesale & retail | 2025 |
| Oakhill Property Solutions Ltd | Real estate | 2024 |
| Oakland Automotive Ltd | Wholesale & retail | 2024 |
| Oakland Decorators Ltd | Construction | 2022 |
| Oakland Electrical Ltd | Manufacturing | 2023 |
| Oaklea Investments Ltd | Real estate | 2011 |
| Oakleaf Architecture Ltd | Professional & scientific | 2016 |
| Oakleaf Estimating Limited | Construction | 2013 |
| Oakleigh Community CIC | Professional & scientific | 2025 |
| Oakley Fencing Contractors Ltd | Construction | 2003 |
| Oakline Healthcare Group Ltd | Administrative & support | 2026 |
| Oakmen Properties Ltd | Real estate | 2022 |
| Oakmere Cottages Ltd | Hospitality | 2025 |
| Oakmere Living Limited | Wholesale & retail | 2026 |
| Oakmill Properties Limited | Extraterritorial | 2004 |
| Oakrise Homes Limited | Real estate | 2025 |
| Oaks View Dore Management Company Limited | Households | 2010 |
| Oaksbridge Fabrications Ltd | Manufacturing | 2021 |
| Oaksbridge Ltd | Construction | 2015 |
| Oakshaw Residents Limited | Hospitality | 2003 |
| Oakstone Homes Limited | Construction | 1994 |
| Oakstone Property Group Ltd | Real estate | 2026 |
| Oakwood Cars Derby Ltd | Wholesale & retail | 2023 |
| Oakwood Data Limited | Information & communication | 2020 |
| Oakwood Forest Tree Services Ltd | Administrative & support | 2020 |
| Oakworth Homes Limited | Manufacturing | 2006 |
| Oalo Security Ltd | Information & communication | 2019 |
| OAS Capital Ltd | Information & communication | 2022 |
| Oasis Market Ltd | Wholesale & retail | 2024 |
| Oasthouse Engineering Ltd. | Wholesale & retail | 2002 |
| Oasthouse Sleevedec Limited | Other services | 2017 |
| Oastmill Limited | Real estate | 1988 |
| Oates Investment Management Ltd | Extraterritorial | 2014 |
| OB Solutionz Ltd | Administrative & support | 2024 |
| OB Waste Solutions Ltd | Water & waste | 2025 |
| Obate Ltd | Professional & scientific | 2025 |
| Obay Homes (SE) Limited | Construction | 2026 |
| Obdios Capital (Holdings NO.1) Limited | Financial services | 2024 |
| Obdios Capital Limited | Financial services | 2016 |
| Obe&P Ltd | Real estate | 2020 |
| Obep Media Limited | Information & communication | 2014 |
| Oberon IT & Photographics Ltd | Information & communication | 1998 |
| Obino & Co Limited | Wholesale & retail | 2022 |
| Objective Creative Limited | Information & communication | 2010 |
| Objective Driven Engineering Limited | Information & communication | 2024 |
| Objective Finance Limited | Professional & scientific | 2008 |
| OBM Medical Limited | Health & social care | 2012 |
| Obosiani Ltd | Hospitality | 2026 |
| Obpi Ltd | Real estate | 2024 |
| OBR Consultancy Services Limited | Information & communication | 2015 |
| Obsidian Path Wellness Services Ltd | Health & social care | 2025 |
| Obviously Optical Ltd | Wholesale & retail | 2022 |
| OCB Entertainment Limited | Arts & recreation | 2014 |
| OCB Logistics Ltd | Transport & logistics | 2025 |
| Occasia Haus Ltd | Professional & scientific | 2026 |
| Occasional Papers Limited | Information & communication | 2009 |
| Occlusion Limited | Health & social care | 2005 |
| Occo Services UK Limited | Administrative & support | 2020 |
| Ocean Blue (Chapeltown) Ltd | Wholesale & retail | 2023 |
| Ocean City Contracting Ltd | Construction | 2024 |
| Ocean Digital Studio Ltd | Professional & scientific | 2017 |
| Ocean Drive (GB) Ltd | Wholesale & retail | 2006 |
| Ocean Rein Ltd | Wholesale & retail | 2026 |
| Ocean Retail Yorkshire Ltd | Wholesale & retail | 2025 |
| Ocean Thai Street Food Ltd | Hospitality | 2025 |
| OCF Holdings Limited | Financial services | 2019 |
| Ocin Ltd | Health & social care | 2014 |
| Ockwells Limited | Extraterritorial | 1991 |
| OCL (Sheffield) Limited | Health & social care | 2003 |
| Oclc (UK) Limited | Information & communication | 1951 |
| Ocpr Limited | Other services | 2017 |
| OCR Medical Limited | Health & social care | 2014 |
| OCR UK Holdings Limited | Financial services | 2024 |
| OCS Inc Limited | Manufacturing | 2018 |
| Octagon Enterprise Ltd | Professional & scientific | 2025 |
| October Drift Ltd | Information & communication | 2016 |
| Octopodes Logistics Ltd | Transport & logistics | 2019 |
| Octopus Legs Ltd | Other services | 2024 |
| Octorbit Ltd | Manufacturing | 2022 |
| Octyne Ltd | Information & communication | 2026 |
| OCU South Humberside Ltd | Information & communication | 1995 |
| Ocular Focus Ltd | Health & social care | 2010 |
| Oculoris Ltd | Health & social care | 2015 |
| Ocvs Limited | Wholesale & retail | 2020 |
| OD Ltd | Wholesale & retail | 2025 |
| ODA Holdings Ltd | Real estate | 2025 |
| Odali Ltd | Hospitality | 2023 |
| Odat Property Investments Ltd | Real estate | 2023 |
| ODB Holdings Limited | Financial services | 2025 |
| ODB Properties Ltd | Real estate | 2024 |
| ODD Girl OUT Productions Limited | Information & communication | 2006 |
| ODD Sock Festival CIC | Arts & recreation | 2024 |
| Oddwood & Co Ltd | Arts & recreation | 2019 |
| Odem Properties Ltd | Construction | 2025 |
| ODM (Omnia DE Magnitudine) Ltd | Professional & scientific | 2025 |