| Office Furniture Advisory Service Limited | Administrative & support | 1987 |
| Office Sense Limited | Wholesale & retail | 2020 |
| Offshore Wind Technical Services Ltd | Construction | 2024 |
| Oftr Racing Limited | Wholesale & retail | 2025 |
| Old College Close Residents Management Company Limited | Households | 1992 |
| Old Convent (Lowestoft) Management Company Limited | Households | 2017 |
| Olde Time Limited | Wholesale & retail | 2010 |
| OLI Food Ltd | Wholesale & retail | 2022 |
| Olive Green Bespoke Joinery Limited | Manufacturing | 2023 |
| Oliver James Estates of East Anglia Limited | Financial services | 2007 |
| Oliver James Estates of Waveney Valley Limited | Real estate | 2020 |
| Oliver James Holdings Limited | Financial services | 2017 |
| Oliver James Investments Limited | Households | 2018 |
| Oliver James Lettings Limited | Real estate | 2023 |
| Oliver James Management Limited | Real estate | 2020 |
| On-Stream Commercial Consultants Ltd | Professional & scientific | 2017 |
| One Call Aviation Services Ltd | Professional & scientific | 2022 |
| One Exclusive Limited | Real estate | 2016 |
| One Lets (EA) Limited | Real estate | 2016 |
| One Place Many Stories CIC | Education | 2024 |
| One T Property Ltd | Real estate | 2023 |
| Onesite Building Products Ltd | Wholesale & retail | 2014 |
| Onesite Commercial Ltd | Real estate | 2021 |
| Onesite Group Ltd | Financial services | 2022 |
| Onesite Hire Ltd | Administrative & support | 2023 |
| Onesite Steel Ltd | Manufacturing | 2023 |
| Only This Ltd | Wholesale & retail | 2023 |
| Onpoint PR Limited | Professional & scientific | 2025 |
| Oodua Asset Ltd | Real estate | 2019 |
| Open Planned Living Limited | Construction | 2024 |
| Opendoors Fundraising Limited | Other services | 2025 |
| Optima Pro UK Limited | Professional & scientific | 2023 |
| Optimal Edge Ltd | Information & communication | 2022 |
| Opus Engineering Services Limited | Manufacturing | 2002 |
| Orange 5 Limited | Extraterritorial | 2026 |
| Orbis Furniture Ltd | Wholesale & retail | 2020 |
| Orchard Accountancy (East Anglia) Limited | Professional & scientific | 2008 |
| Orchardcroft Ltd | Financial services | 2011 |
| Orchardcroft Properties Limited | Real estate | 2015 |
| ORE and Lumber Ltd | Wholesale & retail | 2021 |
| Oriental Food 2023 Ltd | Hospitality | 2023 |
| Orneth LLP | | 2020 |
| OSC Lettings Limited | Real estate | 2019 |
| OSC Services EA Limited | Mining & quarrying | 2012 |
| Oscore Limited | Information & communication | 2020 |
| Oswald Development Limited | Construction | 2018 |
| OTM Solutions Limited | Professional & scientific | 2010 |
| Oulton Broad Apartments Limited | Real estate | 2020 |
| Oulton Broad Dayboats Ltd | Transport & logistics | 2021 |
| Oulton Broad Properties Limited | Real estate | 2013 |
| Oulton Broad Storage Limited | Real estate | 2022 |
| Oulton Cleaning Limited | Other services | 2014 |
| Oulton Food Catering Ltd | Hospitality | 2024 |
| Oulton Home and Scents Ltd | Wholesale & retail | 2023 |
| OUR Better Life Limited | Wholesale & retail | 2021 |
| Outofmk Limited | Transport & logistics | 2023 |
| Over There Films Ltd | Information & communication | 2025 |
| Overy Properties Limited | Real estate | 2020 |
| OWL Engineering and Maintenance Ltd | Professional & scientific | 2024 |
| Oxia Property Ltd | Real estate | 2023 |
| Oynx IT Services Ltd | Information & communication | 2019 |
| P & J. Benterman Builders Limited | Construction | 2004 |
| P D T Services Limited | Professional & scientific | 2006 |
| P J Courier Services Limited | Transport & logistics | 2002 |
| P J Spillings Limited | Real estate | 1986 |
| P K Lynes Heating Services Ltd | Construction | 2017 |
| P Lacey & Associates Limited | Professional & scientific | 2017 |
| P&M Properties East Anglia Ltd | Real estate | 2026 |
| P&W Developments (East Anglia) Ltd | Construction | 2025 |
| P. Blunden Builders Limited | Construction | 2017 |
| P.D.P. Construction Limited | Construction | 1973 |
| P.J. Spillings (Builders) Limited | Construction | 1997 |
| P.R. Offshore Services Limited | Administrative & support | 1996 |
| P.W. Waters Holding Company Ltd | Financial services | 2020 |
| Pablo's Fish Bar Limited | Hospitality | 2024 |
| Paics Limited | Information & communication | 2021 |
| Paige Alicia Limited | Other services | 2026 |
| Pakefield Clinical Limited | Professional & scientific | 2016 |
| Pakefield Coast Protection CIC | Professional & scientific | 2024 |
| Pakefield Pastures Community Interest Company | Health & social care | 2024 |
| Palmers Plumbing (East Anglia) Ltd | Construction | 2026 |
| Palmers Proffesional Painting Ltd | Manufacturing | 2025 |
| Park View Care Home (Liverpool) Limited | Health & social care | 2021 |
| Park View Private Clients Limited | Financial services | 2008 |
| Park View Property Holdings (Liverpool) Limited | Real estate | 2020 |
| Parkers Formal Wear Limited | Wholesale & retail | 2012 |
| Parks Direct Ltd | Real estate | 2014 |
| Parr Rigging and Lifting Services Ltd | Mining & quarrying | 2025 |
| Partington Healthcare Holdings Limited | Health & social care | 2015 |
| Partington Healthcare Limited | Health & social care | 2015 |
| Partners by Design Limited | Professional & scientific | 2002 |
| Patchwork Business Consulting Limited | Administrative & support | 2017 |
| Pathfinder Pro Limited | Professional & scientific | 2026 |
| Patidartrading Ltd | Wholesale & retail | 2025 |
| Paugar Limited | Professional & scientific | 2007 |
| Paul Badger Offshore Services Limited | Other services | 2012 |
| Paul Hubbard Commercial Ltd | Real estate | 2021 |
| Paul Hubbard Ltd | Real estate | 2015 |
| Paul Jermy Limited | Administrative & support | 2002 |
| Paul Mantripp Photography Ltd | Professional & scientific | 2024 |