| Orchard Valley Homes Limited | Construction | 2004 |
| Ordway Home Inspections Limited | Administrative & support | 2006 |
| Orenglas Limited | Financial services | 2021 |
| Orford Capital Limited | Financial services | 2024 |
| Orford Group Limited | Professional & scientific | 2024 |
| Orford Meat Shed Ltd | Hospitality | 2015 |
| Orient Overseas Container Line (Europe) Limited | Professional & scientific | 1983 |
| Oriental & Pacific Frozen Food Company Limited | Wholesale & retail | 1995 |
| Oriental Monkey (UK) Ltd | Wholesale & retail | 2026 |
| Orion Stainless Fabrications Limited | Manufacturing | 2013 |
| Orizont Solutions Ltd | Professional & scientific | 2021 |
| Ormiston Families | Health & social care | 1992 |
| Ormskirk Road Investment Limited | Real estate | 2023 |
| Ornela Ltd | Wholesale & retail | 2010 |
| Orpen House Limited | Administrative & support | 2009 |
| Orqelyx Structures Limited | Information & communication | 2026 |
| Orrilutions Ltd | Administrative & support | 2008 |
| Orry TM Ltd | Construction | 2022 |
| Orsett Refurbishments Ltd | Construction | 2020 |
| Ortan Diving Ltd | Transport & logistics | 2025 |
| Orthogonality Ltd | Information & communication | 2017 |
| Orton Land 2023 Limited | Real estate | 2023 |
| Orvi Limited | Wholesale & retail | 2016 |
| Orwell Advisory Group Limited | Extraterritorial | 2026 |
| Orwell Advisory Limited | Extraterritorial | 2026 |
| Orwell Arts Ltd | Arts & recreation | 2023 |
| Orwell Boat Maintenance Ltd | Manufacturing | 2024 |
| Orwell Build (Clacton BTL) Limited | Real estate | 2025 |
| Orwell Carpentry & Building Ltd | Construction | 2023 |
| Orwell Communications Ltd | Administrative & support | 2022 |
| Orwell Container Services Limited | Transport & logistics | 2024 |
| Orwell Contract Tiling Limited | Construction | 2019 |
| Orwell Facilities Management Limited | Transport & logistics | 2024 |
| Orwell Grove (Finbars Walk) Management Company Limited | Households | 1995 |
| Orwell Homes Limited | Construction | 1997 |
| Orwell LAB Limited | Manufacturing | 2025 |
| Orwell Logistics Ltd | Transport & logistics | 2025 |
| Orwell Medical Limited | Extraterritorial | 2026 |
| Orwell Model Railways Ltd | Wholesale & retail | 2017 |
| Orwell Mortgages Ltd | Financial services | 2021 |
| Orwell Multi Academy Trust | Education | 2017 |
| Orwell Park Limited | Real estate | 1997 |
| Orwell Park School Educational Trust Limited | Education | 1967 |
| Orwell Park Village Limited | Professional & scientific | 1997 |
| Orwell Pet Cremation Service Ltd | Other services | 2002 |
| Orwell Pine Co Limited | Manufacturing | 1998 |
| Orwell Property Company Limited | Real estate | 1993 |
| Orwell River Cruises Limited | Transport & logistics | 2001 |
| Orwell Services Ltd | Administrative & support | 2025 |
| Orwell Structural Engineers Limited | Professional & scientific | 2020 |
| Orwell Supreme Ltd | Real estate | 2020 |
| Orwell Television Ltd | Information & communication | 2020 |
| Orwell Ventures Limited | Construction | 2022 |
| Orwell View Management Company Limited | Households | 1995 |
| Orwell Web Solutions Limited | Information & communication | 2014 |
| Orwell Yacht Club Limited | Arts & recreation | 2024 |
| Orwells Furniture Limited | Professional & scientific | 2006 |
| Orwells Limited | Professional & scientific | 2006 |
| OS Composites Ltd | Wholesale & retail | 2020 |
| OS24 Ltd | Administrative & support | 2024 |
| Osan Trans Ltd | Transport & logistics | 2024 |
| Osborne Kitchen Designs Ltd | Construction | 2023 |
| Osbourne Young Limited | Manufacturing | 2023 |
| Osgad Medico-Legal Ltd | Health & social care | 2012 |
| Osiris Plumbing & Heating Ltd | Construction | 2009 |
| Oskar Invest Ltd | Wholesale & retail | 2022 |
| Osko Limited | Professional & scientific | 2011 |
| Osnail Ltd | Information & communication | 2026 |
| OSR Recruitment Services Limited | Administrative & support | 1999 |
| Ossia Consulting Limited | Professional & scientific | 2022 |
| Osteopath in Suffolk Ltd | Health & social care | 2025 |
| Osuapp Ltd | Information & communication | 2017 |
| OT Grub Limited | Hospitality | 2019 |
| Otter's Holt Management Company Ltd | Households | 2021 |
| Otters END Management Company Limited | Households | 2002 |
| Ottoman Cuisine Limited | Hospitality | 2015 |
| OUR House Clearance Ltd | Water & waste | 2026 |
| OUR Place Sustainable Development Limited | Construction | 2016 |
| OUR Touch Clean Ltd | Administrative & support | 2025 |
| Ouranos Services LLP | | 2022 |
| Ourshoppinghub Ltd | Wholesale & retail | 2025 |
| OUT Loud Music Community Interest Company | Information & communication | 2014 |
| OUT of Office Travel Ltd | Administrative & support | 2022 |
| Outcomes Thinking Ltd | Information & communication | 2020 |
| Outdoor Technology Ltd | Professional & scientific | 2026 |
| Outlet Prices Direct International Ltd | Manufacturing | 2024 |
| Outreach FX Limited | Education | 2020 |
| Outreach Sports Hub Limited | Arts & recreation | 2024 |
| Outstanding Futures CIC | Education | 2019 |
| Ovac Ltd | Wholesale & retail | 2025 |
| Overland Events Limited | Arts & recreation | 2014 |
| Overlanding West Africa Ltd | Administrative & support | 2010 |
| OVI Logistic Services Ltd | Transport & logistics | 2017 |
| Ovoskins Ltd | Wholesale & retail | 2025 |
| Ovrly Ltd | Wholesale & retail | 2025 |
| Owen Martial Arts Limited | Education | 2019 |
| OWL Bookbinding Limited | Information & communication | 2016 |
| Ownr Solutions Limited | Information & communication | 2022 |
| Owsley Limited | Arts & recreation | 2019 |
| Oxford Electromagnetic Solutions Limited | Professional & scientific | 2010 |