| Nxtgen SNS Limited | Information & communication | 2023 |
| NY Industrial Roofing and Cladding Limited | Construction | 2016 |
| O & B Cleaning Services (Ipswich) Limited | Administrative & support | 2017 |
| O K Delivery Ltd | Transport & logistics | 2019 |
| O'Neill Consultancy Ltd | Administrative & support | 2022 |
| O'Rourke Garden Services Ltd | Administrative & support | 2020 |
| O.B.Denison & SON Ltd | Wholesale & retail | 2020 |
| O.Brader Plumbing and Heating Ltd | Construction | 2026 |
| O.G. Barnard & Sons Limited | Wholesale & retail | 1945 |
| Oak Accountancy & Business Services Limited | Professional & scientific | 2004 |
| Oak Beeches Investments Limited | Real estate | 2024 |
| Oak Bridge Ipswich Ltd | Financial services | 2020 |
| Oak Employment Ltd | Administrative & support | 2021 |
| Oak Financial Limited | Financial services | 2004 |
| Oak Green Enterprises Limited | Administrative & support | 2009 |
| Oak Grove (Eyke) Management Company Limited | Households | 2025 |
| Oak Grove Management Company Limited | Real estate | 1999 |
| Oak House (Woodbridge) Limited | Administrative & support | 2001 |
| Oak House Farm Limited | Agriculture & fishing | 1991 |
| Oakhaven Limited | Professional & scientific | 2006 |
| Oakhill Management Company (Ipswich) Limited | Households | 1999 |
| Oakhurst (East Anglia) Limited | Real estate | 1988 |
| Oakkey Holdings Ltd | Financial services | 2024 |
| Oakland Hall Day Nursery Limited | Education | 2012 |
| Oaklands (South Wootton) Management Company Limited | Households | 2018 |
| Oaklands Property Management Company Limited | Households | 1998 |
| Oakley Horsebox and Coach Builders Ltd | Manufacturing | 2015 |
| Oakley Park Mulbarton Management Company Limited | Households | 2016 |
| Oakmere Holding Group Limited | Financial services | 2012 |
| Oakmere Solutions Limited | Professional & scientific | 2009 |
| Oakmont Development SPV1 Limited | Construction | 2025 |
| Oakpak Security Limited | Administrative & support | 2024 |
| Oakpark Security Systems Limited | Administrative & support | 1995 |
| Oaks Carpentry Ltd | Construction | 2022 |
| Oaksmere Commercial Finance Brokers Ltd | Financial services | 2026 |
| Oaksmere Design Limited | Professional & scientific | 2016 |
| Oaksmere Holdings Limited | Financial services | 2021 |
| Oakwell Advisory Limited | Professional & scientific | 2023 |
| Oakwood Technology Group Limited | Construction | 1989 |
| Oasis Ipswich Limited | Other services | 2025 |
| Oasis Medical Center Ltd | Health & social care | 2021 |
| Oasis Second Hand Parts Ltd | Wholesale & retail | 2024 |
| Oban Queens Hotel Limited | Hospitality | 2017 |
| Oban Queens Management Limited | Hospitality | 2017 |
| Oban Regent Assets Limited | Hospitality | 2020 |
| Oban Regent Management Limited | Hospitality | 2020 |
| Oban Street (Ipswich) Management Company Limited | Households | 2004 |
| Obarski Homes Limited | Real estate | 2019 |
| Oblix Properties Ltd | Real estate | 2022 |
| Observation Grounds Ltd | Real estate | 2019 |
| Obsidian Films Ltd | Information & communication | 2011 |
| OC Carpentry & Construction Limited | Construction | 2013 |
| OC Homes Limited | Construction | 2023 |
| Occidental Grains Ltd | Professional & scientific | 2008 |
| Ocean Data Interface Ltd | Professional & scientific | 2014 |
| Ocean Galaxy Ltd | Wholesale & retail | 2023 |
| Ocean Global Line Holdings Limited | Financial services | 2022 |
| Ocean Global Line Limited | Transport & logistics | 2019 |
| Ocean Platter Ltd | Hospitality | 2020 |
| Ocean Zenith Co. Limited | Transport & logistics | 2012 |
| OCS Food Co Limited | Hospitality | 1990 |
| OCS Group UK Limited | Administrative & support | 1995 |
| OCS Group Uk&I Limited | Administrative & support | 2014 |
| OCS Managed Services Limited | Hospitality | 2004 |
| OCS Pest Control Limited | Administrative & support | 2000 |
| OCS Security Limited | Administrative & support | 2002 |
| OCS Uk&I Group Holdings Limited | Administrative & support | 1999 |
| OCS Uk&I Holdings Limited | Professional & scientific | 2018 |
| OCS Uk&I Limited | Administrative & support | 2007 |
| Octacare Limited | Health & social care | 2016 |
| Octopus Capture Apps LP | | 2024 |
| Octopus Systems Limited | Information & communication | 2012 |
| ODD Flock Ltd | Professional & scientific | 2025 |
| ODD Ltd | Professional & scientific | 2023 |
| Oddity Holdings Ltd | Real estate | 2025 |
| Odek Ecom Vitals Ltd | Wholesale & retail | 2024 |
| Odigos Ltd | Information & communication | 2020 |
| Odisi Sport Limited | Wholesale & retail | 2020 |
| ODS Solutions Limited | Information & communication | 2016 |
| ODX Group (Suffolk) Ltd | Construction | 2002 |
| Odyssey Connect Limited | Administrative & support | 2025 |
| OEB Clearance Limited | Wholesale & retail | 2021 |
| Oepfc UK Limited | Wholesale & retail | 2024 |
| Offbeat Education Ltd | Education | 2025 |
| Offbeat Tickets Limited | Administrative & support | 2021 |
| Offord Electrical Limited | Construction | 2022 |
| Oggi Scaffolding Limited | Construction | 2014 |
| OHF2 Limited | Professional & scientific | 2025 |
| OIL Boilers & Heating Ltd | Construction | 2023 |
| OJC Haulage Ltd | Transport & logistics | 2020 |
| OJH Sports MED Limited | Health & social care | 2026 |
| OJP Estates Ltd | Real estate | 2024 |
| OJP Sports Management Limited | Arts & recreation | 2021 |
| OK Kebab Ltd | Hospitality | 2025 |
| Ok-Supreme Motors Limited | Manufacturing | 2016 |
| OKD Limited | Information & communication | 2010 |
| Okohaus Operations Limited | Construction | 2024 |
| Okohaus UK Limited | Wholesale & retail | 2020 |
| OL Global Logistics Ltd | Other services | 2024 |
| OLADOTUNDADA247HEALTHCARE Ltd | Professional & scientific | 2025 |