| OBH Development Limited | Extraterritorial | 2013 |
| OBH Limited | Extraterritorial | 2013 |
| OBH Management Limited | Households | 2015 |
| OBI & Stevenson Limited | Professional & scientific | 2020 |
| Obiez Ltd | Transport & logistics | 2016 |
| Obiwon Ltd | Extraterritorial | 2024 |
| Observational and Pragmatic Research International Limited | Professional & scientific | 2001 |
| Obsidian Global Sourcing Limited | Administrative & support | 2025 |
| Obychin UK Ltd | Health & social care | 2025 |
| Occasions (Cromer) Ltd | Wholesale & retail | 2019 |
| Ocean Driven Media Ltd | Information & communication | 2023 |
| Ocean Fish Bar (Telford) Limited | Hospitality | 2015 |
| Ocean Leaf Ltd | Wholesale & retail | 2022 |
| Ocean Retreat Norfolk Ltd | Hospitality | 2022 |
| Ocean Trans UK Limited | Transport & logistics | 2017 |
| Oceanic Ecological Surveys Limited | Professional & scientific | 2017 |
| Oceanpact Maritime Limited | Professional & scientific | 2014 |
| Oceans Fish Bar Limited | Hospitality | 2019 |
| Oceanstrive Ltd | Professional & scientific | 2019 |
| Ochre Interiors Ltd | Construction | 2019 |
| OCI Partnerships Limited | Professional & scientific | 2013 |
| Ockerhill Stores Limited | Wholesale & retail | 2018 |
| OCS IT Management Company Ltd | Administrative & support | 2016 |
| Octabit Ltd | Information & communication | 2017 |
| Octagon Barn Ltd | Wholesale & retail | 2014 |
| Octagon Management Company (Cromer) Limited | Real estate | 2012 |
| Octagon Training Limited | Education | 2026 |
| Octasphere Limited | Information & communication | 2026 |
| Octavolve Care Ltd | Education | 2020 |
| Octega Limited | Information & communication | 2026 |
| October 26TH Atelier Ltd. | Manufacturing | 2015 |
| Oculus (Franchise) Ltd | Administrative & support | 2012 |
| Oculus (Norwich) Limited | Health & social care | 2002 |
| Odao Limited | Professional & scientific | 2017 |
| Oddys Trading Co Limited | Wholesale & retail | 2019 |
| Odin Enterprises Limited | Real estate | 2014 |
| Odon Fashion Limited | Other services | 2022 |
| ODP Competitions Limited | Wholesale & retail | 2025 |
| ODP Enterprises Limited | Other services | 2021 |
| ODR Management Ltd | Administrative & support | 2025 |
| Odruvisi LLP | | 2023 |
| Odutemu Ltd | Information & communication | 2024 |
| Odysea Engineering Consultants Ltd | Professional & scientific | 2024 |
| Odyssey Consulting Ltd | Professional & scientific | 2024 |
| Odyssey Development Consultancy Limited | Professional & scientific | 2020 |
| Odyssey for Change Limited | Professional & scientific | 2010 |
| Odyssey Multimedia Limited | Professional & scientific | 2024 |
| OFF Beat Lounge Limited | Wholesale & retail | 2014 |
| OFF the Record Counselling Service (Norfolk) Limited | Health & social care | 2000 |
| OFF the Twig CIC | Health & social care | 2023 |
| OFF the Wall Outdoor Limited | Professional & scientific | 2014 |
| Office Brew Solutions Ltd | Wholesale & retail | 2024 |
| Office Furniture Scene Limited | Wholesale & retail | 2010 |
| Office IT (UK) Limited | Information & communication | 2013 |
| Office Products International Limited | Information & communication | 1990 |
| Office Water Supplies Limited | Administrative & support | 2015 |
| Officeflow Ltd | Administrative & support | 2019 |
| Offshore Wind Management Ltd | Other services | 2016 |
| Offshorediver Limited | Professional & scientific | 2010 |
| Offshorescope Ltd | Information & communication | 2025 |
| OFT Global Limited | Transport & logistics | 2013 |
| OGD Scaffolding Limited | Construction | 2013 |
| OGE Solutions Ltd | Administrative & support | 2016 |
| Ogilvie Rich Asset Management Limited | Real estate | 2022 |
| Ogilvy House Limited | Hospitality | 2011 |
| OGJ Catering Services Ltd | Hospitality | 2023 |
| OGUZ68 Ltd | Wholesale & retail | 2024 |
| OH! QS Practice Limited | Professional & scientific | 2018 |
| Ohara L Ltd | Professional & scientific | 2019 |
| OHD (2011) Limited | Construction | 2011 |
| Ohdemetric Limited | Professional & scientific | 2022 |
| OHH Corey Limited | Wholesale & retail | 2026 |
| OHK Limited | Wholesale & retail | 2023 |
| OHM Developments Ltd | Real estate | 2021 |
| OHM Ventures Ltd | Real estate | 2022 |
| Oichi Kombucha Limited | Manufacturing | 2022 |
| Oilfield Logistics Management Limited | Mining & quarrying | 2001 |
| Oiltag Limited | Professional & scientific | 2012 |
| Oishii Kitchen Ltd | Wholesale & retail | 2025 |
| Oivallus Limited | Professional & scientific | 2016 |
| OJ Horizon Holdings Limited | Real estate | 2026 |
| Ojay Ltd | Health & social care | 2021 |
| Ojay's (N E) Ltd | Hospitality | 2017 |
| OJE Properties Limited | Hospitality | 2015 |
| OJF Paintwork Ltd | Wholesale & retail | 2024 |
| OJP Plumbing Limited | Construction | 2025 |
| OJS Consultancy Ltd | Professional & scientific | 2023 |
| Okashi Kitchen Limited | Hospitality | 2024 |
| OKM Media Ltd | Professional & scientific | 2012 |
| Okra Associates Ltd | Financial services | 2009 |
| Okra Consulting Ltd | Professional & scientific | 2018 |
| Olael Consultancy Ltd | Administrative & support | 2016 |
| Olakit Ltd | Wholesale & retail | 2025 |
| Olas Engineering Ltd | Professional & scientific | 2024 |
| Olata Fashions Ltd | Wholesale & retail | 2015 |
| Olawande Co Ltd | Other services | 2024 |
| Old Allen Road Energy Centre Limited | Energy | 2022 |
| Old Catton Stores Limited | Wholesale & retail | 2024 |
| Old Coach House Services Limited | Professional & scientific | 2019 |
| Old Fashioned Holdings Ltd | Financial services | 2020 |