| Oakley Park Properties Ltd | Real estate | 2017 |
| Oakmere Manor Farm Limited | Agriculture & fishing | 2023 |
| Oakmere NF Ltd | Real estate | 2024 |
| Oakmount & Partners ( Property SPV 2 ) Limited | Health & social care | 2025 |
| Oakmount & Partners ( Property SPV 3 ) Limited | Real estate | 2025 |
| Oakmount & Partners ( Property SPV 4 ) Limited | Real estate | 2025 |
| Oakmount & Partners ( Property SPV 5 ) Limited | Real estate | 2025 |
| Oaks Exhibition & Joinery Contractors Limited | Construction | 2006 |
| Oaks Town Properties Limited | Administrative & support | 1996 |
| Oaktree Healthcare Limited | Health & social care | 2012 |
| Oakwell Capital Limited | Financial services | 2014 |
| Oakwood Home Learning Limited | Education | 2016 |
| Oakwood Kitchen Design Consultants Limited | Manufacturing | 1983 |
| Oakwood Kitchens Limited | Extraterritorial | 2010 |
| Oakwood Property Lettings Limited | Real estate | 2017 |
| Oasis Care Support Services Limited | Health & social care | 2000 |
| Oasis Homecare Limited | Health & social care | 2024 |
| Oats Recruitment Limited | Administrative & support | 2019 |
| Obas Concept Ltd | Transport & logistics | 2025 |
| Objective Group Limited | Professional & scientific | 2022 |
| Objective Strategies Limited | Professional & scientific | 2009 |
| Objective World Limited | Financial services | 2023 |
| Ocas Advisory Ltd | Health & social care | 2018 |
| Occta Limited | Information & communication | 2022 |
| Occurrent Ltd | Information & communication | 2025 |
| OCD Services Kirklees Ltd | Other services | 2011 |
| Ocean Care Ltd | Health & social care | 2020 |
| Ocean Cleaning Services Ltd | Other services | 2009 |
| Ocean Print Limited | Manufacturing | 2012 |
| Ocean Property Asset Limited | Real estate | 2025 |
| Ocean Technical Limited | Manufacturing | 2020 |
| Oceans GMB Limited | Transport & logistics | 2015 |
| Ocff Property Services Ltd | Professional & scientific | 2022 |
| Ochiltree Stores Ltd | Wholesale & retail | 2016 |
| Ocholo Limited | Hospitality | 2019 |
| Oculus Wealth Management (Huddersfield) Limited | Financial services | 2018 |
| Ocusure Limited | Wholesale & retail | 2005 |
| OD Contractors Ltd | Construction | 2019 |
| Odiss Fashion Collections Ltd | Extraterritorial | 2025 |
| OEM Group Limited | Wholesale & retail | 1986 |
| OEM Plates Ltd | Wholesale & retail | 2023 |
| OF Scent. Ltd | Manufacturing | 2025 |
| OFF the Wall Tailoring Limited | Manufacturing | 2021 |
| Off-White Construction Ltd | Manufacturing | 2024 |
| Office Heft Limited | Professional & scientific | 2024 |
| Official Products Ltd | Wholesale & retail | 2022 |
| Offtide Ltd | Wholesale & retail | 2023 |
| OG Wines Limited | Wholesale & retail | 2024 |
| Ogam Jacquard Weavers Ltd | Manufacturing | 2014 |
| Ogden Water Limited | Construction | 2008 |
| Ogel C-S Limited | Real estate | 2023 |
| Ogga Ltd | Wholesale & retail | 2023 |
| OGS Walling Ltd | Construction | 2024 |
| Ohana Healing Collective Ltd | Manufacturing | 2025 |
| Ohms Limited | Wholesale & retail | 2003 |
| OI Dumplings Ltd | Hospitality | 2021 |
| Oilsealsrus Limited | Wholesale & retail | 2025 |
| OJ Home Developments Ltd | Professional & scientific | 2007 |
| Okeways Limited | Wholesale & retail | 2024 |
| Olalizzy Beauty Arena Ltd | Other services | 2025 |
| Olan Technical Services Limited | Professional & scientific | 2018 |
| Olbya Ltd | Other services | 2024 |
| Old Beech Farm Management Co Limited | Households | 2022 |
| Old Oak Systems Limited | Information & communication | 2017 |
| Old Town Mill Management Company Limited | Households | 2023 |
| Old YEW Barn Limited | Professional & scientific | 2016 |
| Oldbellcampsall Limited | Hospitality | 2023 |
| Olde ENG Fisheries (Huddersfield) Ltd | Hospitality | 2026 |
| Olde ENG Fisheries Ltd | Hospitality | 2021 |
| Oldfield Cars Ltd | Transport & logistics | 2024 |
| Oldroyd Property Lettings Limited | Administrative & support | 2003 |
| Olicana Ventures Limited | Financial services | 2023 |
| Olik Limited | Information & communication | 2010 |
| Oliru Developments Limited | Construction | 2023 |
| Olive & Grey's Interior Design and Consultancy Ltd | Professional & scientific | 2021 |
| Olive & Thistle Holdings Ltd | Financial services | 2026 |
| Olive and Thistle Group Ltd | Construction | 2025 |
| Olive Branch Properties Ltd | Real estate | 2014 |
| Olivemae Ltd | Administrative & support | 2019 |
| Oliver Grange Enterprises Ltd | Other services | 2015 |
| Oliver Grange Ltd | Professional & scientific | 2009 |
| Oliveto & Co. Limited | Real estate | 2020 |
| Olivia Wray Design Limited | Professional & scientific | 2023 |
| Olutayo Properties Ltd | Real estate | 2020 |
| Olympus Technologies Limited | Manufacturing | 1987 |
| Olytec Limited | Professional & scientific | 2015 |
| OM IS Where the Heart IS Limited | Hospitality | 2016 |
| OM IS Where the Heart IS Yoga Limited | Arts & recreation | 2018 |
| OM7 Limited | Information & communication | 2004 |
| Omane International Ltd | Wholesale & retail | 2023 |
| Omara Developments Ltd | Real estate | 2025 |
| OMC England Limited | Manufacturing | 2015 |
| Omegasigma Holdings Limited | Real estate | 2021 |
| OMF Accountants Ltd | Professional & scientific | 2010 |
| Omni Mortgage Club Limited | Financial services | 2026 |
| Omni Pick Limited | Wholesale & retail | 2026 |
| Omnicore Intermediary Solutions Limited | Financial services | 2002 |
| Omnicore Services Limited | Other services | 2017 |
| Omnicorp Energy Ltd | Energy | 2024 |
| Omnicorp Group Ltd | Financial services | 2023 |