| Oh&Co Ltd | Information & communication | 2017 |
| Oh-Saucey Ltd | Manufacturing | 2021 |
| Ohana House Limited | Real estate | 2018 |
| Ohana Travel Group Ltd | Hospitality | 2026 |
| Ohanaleeds Ltd | Manufacturing | 2023 |
| OHS Limited | Professional & scientific | 2004 |
| Ohstrio Ltd | Wholesale & retail | 2025 |
| Ohzaza Clinic Ltd | Health & social care | 2025 |
| Ohzaza Labs Ltd | Health & social care | 2025 |
| Ohzaza Ltd | Health & social care | 2026 |
| OIC Run-Off Limited | Financial services | 1931 |
| Oidia Ltd | Construction | 2018 |
| OIL Maintenance Systems Ltd | Mining & quarrying | 2017 |
| Oilfield Asset Management Limited | Financial services | 2022 |
| Oilfield Assets Limited | Financial services | 2022 |
| Oilgear | Manufacturing | 1985 |
| Oilgear European Holdings Limited | Manufacturing | 2007 |
| Oilgear Towler Limited | Manufacturing | 1956 |
| Oinkco Limited | Administrative & support | 2025 |
| Oirl Realisations (2025) Limited | Hospitality | 2005 |
| Oishi.Kitchen Ltd | Hospitality | 2023 |
| Oisoi Sheffiled Ltd | Extraterritorial | 2024 |
| OJ Cleaning Services Ltd | Administrative & support | 2021 |
| OJG Joinery & Construction Ltd | Construction | 2021 |
| OJG Joinery & Lanscaping Ltd | Construction | 2026 |
| OJH Consulting Ltd | Administrative & support | 2015 |
| OJI Distribution Ltd | Wholesale & retail | 2025 |
| Ojla Lets Ltd | Real estate | 2016 |
| Ojmg Consulting Ltd | Other services | 2023 |
| OJR Groundwork's Ltd | Construction | 2026 |
| Ojuolape Arcade Ltd | Real estate | 2019 |
| OJW Creative Ltd | Wholesale & retail | 2024 |
| OK Equine Ltd | Agriculture & fishing | 2022 |
| OK Fast Food Ltd | Hospitality | 2018 |
| Okami Clinical Consultancy Ltd | Professional & scientific | 2025 |
| Okapi Fashions Ltd | Wholesale & retail | 2024 |
| Okapi Train UK Ltd | Professional & scientific | 2025 |
| Okbringiton Ltd | Education | 2017 |
| Okey Autos Ltd | Professional & scientific | 2020 |
| Okproductions Ltd | Transport & logistics | 2026 |
| Okusanya Consulting Ltd | Information & communication | 2023 |
| Okyeman Market Ltd | Wholesale & retail | 2026 |
| OL' MAN Swanny CIC | Education | 2023 |
| OLA Aesthetics Ltd | Other services | 2022 |
| Olafe Foods Ltd | Hospitality | 2022 |
| Olahs Place Group Ltd | Administrative & support | 2026 |
| Olalla Consulting Ltd | Professional & scientific | 2025 |
| Olamic Skin Limited | Other services | 2021 |
| Olandok Ltd | Real estate | 2022 |
| Olast ( Cheshire Oaks) Ltd | Real estate | 2018 |
| Olast (Beverley) Ltd | Real estate | 2018 |
| Olast (Swindon) Ltd | Real estate | 2018 |
| Olast (York) Ltd | Real estate | 2018 |
| Olast 7 Ltd | Real estate | 2016 |
| OLAST3 Limited | Wholesale & retail | 2013 |
| Olatayo African Store Ltd | Wholesale & retail | 2026 |
| Olawuyiservices Limited | Administrative & support | 2022 |
| Olbe Developments Limited | Construction | 2018 |
| Old Box Factory Ltd | Households | 2024 |
| Old Cattle Market Limited | Construction | 2018 |
| Old Chapel Music 25 CIC | Information & communication | 2025 |
| Old Chapel Music CIC | Arts & recreation | 2007 |
| Old Convent Ltd | Real estate | 2019 |
| Old Eagle Motorcycles Ltd | Wholesale & retail | 2025 |
| Old Hopkinson Drive Management Company Limited | Households | 2018 |
| Old Lane Express LS Ltd | Wholesale & retail | 2017 |
| Old Lane PO Ltd | Transport & logistics | 2025 |
| Old Oak Property Services Ltd | Construction | 2023 |
| Old Orchard Investments Ltd. | Real estate | 2015 |
| Old Park Interiors Limited | Real estate | 2006 |
| Old Presbytery Birstall Management Company Limited | Households | 2023 |
| Old School Lofts (Freehold) Limited | Professional & scientific | 2008 |
| Old School Lofts Ltd | Professional & scientific | 2004 |
| Old School Mews Management (Otley) Limited | Households | 2006 |
| Old School Movies Ltd | Wholesale & retail | 2019 |
| Old Siam Supermarket Ltd | Wholesale & retail | 2013 |
| Older People's Action in the Locality | Health & social care | 2009 |
| Olderthan Limited | Real estate | 2014 |
| Oldfield Barber Limited | Other services | 2022 |
| Oldfield PUB Company Ltd | Hospitality | 2022 |
| Oldfield Realty Limited | Construction | 1987 |
| Oldroyd Consultants Ltd | Professional & scientific | 2025 |
| Oldroyd Property Management Limited | Real estate | 2018 |
| Olds Brothers Ltd | Transport & logistics | 2023 |
| Oldstone Legal Limited | Professional & scientific | 2026 |
| Oleksijs Engineering Limited | Professional & scientific | 2018 |
| Olemax Ltd | Transport & logistics | 2025 |
| Olerni Azchem.Engr Limited | Professional & scientific | 2022 |
| Olia Properties Limited | Real estate | 2023 |
| Olicana Investments | Financial services | 2020 |
| Olicana Strategy & Support Ltd | Professional & scientific | 2026 |
| Olifant Limited | Information & communication | 1997 |
| Oliraw Limited | Real estate | 2021 |
| Olive & TAN Travel Co Ltd | Administrative & support | 2025 |
| Olive Food (Leeds) 2 Ltd | Hospitality | 2026 |
| Olive Group Investments Ltd | Real estate | 2025 |
| Olive Ocean Social Work Ltd | Health & social care | 2026 |
| Oliver & Co., C.A. Limited | Professional & scientific | 2014 |
| Oliver Clippers Ltd. | Other services | 2025 |
| Oliver Cowan Bridge Club Virtual Limited | Other services | 2010 |