| Ocean House (Chepstow) RTM Company Limited | Households | 2019 |
| Ocean IB Ltd | Financial services | 2025 |
| Ocean Laundry Linen Services Limited | Other services | 2024 |
| Ocean Laundry Ltd | Other services | 2017 |
| Ocean Laundry Workwear Services Limited | Other services | 2024 |
| Ocean LES Ltd | Real estate | 2025 |
| Ocean Letting and Management Limited | Real estate | 2004 |
| Ocean Music Limited | Arts & recreation | 1978 |
| Ocean Places Ltd | Real estate | 2019 |
| Ocean Pots Limited | Agriculture & fishing | 2013 |
| Ocean Property Lawyers Ltd | Professional & scientific | 2000 |
| Ocean Property Services (Group) Limited | Professional & scientific | 2012 |
| Ocean Rock Adventure Ltd | Education | 2010 |
| Ocean Service Group Ltd. | Wholesale & retail | 2024 |
| Ocean Seven Developments Limited | Construction | 2006 |
| Ocean Surveyors Ltd | Administrative & support | 2000 |
| Oceanic Films Limited | Information & communication | 2017 |
| Oceanic Properties Limited | Real estate | 2003 |
| Oceanlake Limited | Households | 1965 |
| Oceanne Limited | Other services | 2012 |
| OCEANNE1 Limited | Professional & scientific | 2023 |
| Oceans 25 Limited | Information & communication | 2022 |
| Oceans Alive Limited | Wholesale & retail | 2015 |
| Oceantime Ltd | Wholesale & retail | 2025 |
| Oceanwood Property Services Limited | Real estate | 2019 |
| Ocha & Co. Green Tea Limited | Wholesale & retail | 2015 |
| Ochefe Ltd | Manufacturing | 2026 |
| Ochre Productions Ltd | Arts & recreation | 2022 |
| Ochre Solutions (Holdings) Limited | Health & social care | 2004 |
| Ochre Solutions Limited | Health & social care | 2004 |
| OCM Ltd | Financial services | 2024 |
| Oconnell Real Estate (Annesley) Limited | Real estate | 2017 |
| OCP Consulting Limited | Wholesale & retail | 2024 |
| Ocri Ltd | Real estate | 2020 |
| Octagon Consultancy Limited | Financial services | 2011 |
| Octagon Enterprise Holdings Limited | Financial services | 2022 |
| Octagon Healthcare Funding PLC | Administrative & support | 2003 |
| Octagon Healthcare Group Limited | Professional & scientific | 2003 |
| Octagon Healthcare Holdings (Norwich) Limited | Professional & scientific | 1997 |
| Octagon Healthcare Limited | Other services | 1995 |
| Octagon Treasure Limited | Administrative & support | 2015 |
| Octane Accountants Limited | Professional & scientific | 2020 |
| Octarine Investments Limited | Financial services | 1999 |
| Octavated Audio Ltd | Information & communication | 2024 |
| Octavius Hunt Holdings Ltd | Financial services | 2017 |
| Octavius Hunt Limited | Manufacturing | 1998 |
| Octavius Ventures Ltd | Information & communication | 2026 |
| Octopos Limited | Administrative & support | 2006 |
| Octopreneur Intelligence Limited | Professional & scientific | 2023 |
| Octopus Flooring Ltd | Construction | 2014 |
| Octopus Immersive Laboratory Ltd. | Information & communication | 2015 |
| Octopus Technologies Ltd | Information & communication | 1997 |
| Ocucon Software Ltd | Information & communication | 2019 |
| Ocul Engineering Limited | Other services | 2007 |
| Oculoart Limited | Health & social care | 2024 |
| Oculus Legal Group Limited | Administrative & support | 2023 |
| Oculus Technology Solutions Limited | Administrative & support | 2024 |
| Oculus Wealth Management (Bath) Limited | Financial services | 2013 |
| Ocurro (Bscl) Ltd | Information & communication | 1990 |
| Ocurro (Tech-Ology) Ltd | Information & communication | 2014 |
| Ocurro Ltd | Professional & scientific | 2010 |
| OD One Consulting Ltd | Information & communication | 2013 |
| ODD Jobs Solutions Limited | Construction | 2025 |
| Oddball CIC | Arts & recreation | 2026 |
| Oddity Creative Limited | Professional & scientific | 2023 |
| Oddly Moving Ltd | Arts & recreation | 2020 |
| Oddogo Ltd | Information & communication | 2024 |
| Oddprints Ltd | Information & communication | 2016 |
| Odds & Todds Ltd | Wholesale & retail | 1999 |
| Odds and Dogs Ltd | Manufacturing | 2013 |
| Oddsox Ltd | Wholesale & retail | 2011 |
| Oddventures Ltd | Information & communication | 2021 |
| Odeh Homes Limited | Health & social care | 2006 |
| Odeyemi Property Group Ltd | Real estate | 2020 |
| Odiel Limited | Construction | 2026 |
| Odinns Ltd | Hospitality | 2014 |
| Odjc Ltd | Administrative & support | 2025 |
| Odowaa Limited | Transport & logistics | 2019 |
| Odoyo Ltd | Hospitality | 2026 |
| ODR Limited | Construction | 2011 |
| Odrod Ltd | Real estate | 2020 |
| Odrone Ltd | Administrative & support | 2025 |
| Odyssey World Limited | Extraterritorial | 2012 |
| OF the Coven Ltd | Information & communication | 2026 |
| OFC Services Ltd | Transport & logistics | 2026 |
| OFF Grid Adventures Ltd | Education | 2018 |
| OFF the Cuff (Bristol) Ltd | Real estate | 2025 |
| OFF the Fence Productions Limited | Information & communication | 2004 |
| OFF the Post Ltd | Information & communication | 2026 |
| OFF the Record (Bristol) | Health & social care | 2001 |
| Off-Kilter Pictures Limited | Information & communication | 2024 |
| Offbeat Spaces Ltd | Real estate | 2020 |
| Offcorp Limited | Professional & scientific | 2013 |
| Offer Investments Limited | Real estate | 2024 |
| Offer Property Limited | Construction | 2020 |
| Offerzone Property Management Limited | Households | 1988 |
| Offiah Shaw Pelvic Health Ltd | Health & social care | 2025 |
| Office 24 Ltd | Administrative & support | 2005 |
| Office Coach Ltd | Information & communication | 2010 |
| Office Corr Higgins Ltd | Professional & scientific | 2022 |