| Old Hall Farm Barns Management Company Limited | Water & waste | 2006 |
| Old Hall Holdings Limited | Construction | 2021 |
| Old Lakenham Hall Residents Association Limited | Real estate | 1978 |
| Old Laundry Court Owners Association Limited | Other services | 2000 |
| Old Miller's Wharf Norwich Limited | Households | 2006 |
| Old Millers Wharf Limited | Real estate | 2024 |
| Old Mint Yard Apartments Ltd | Real estate | 2024 |
| Old Mint Yard Ltd | Real estate | 2024 |
| Old Pump House Court (Norwich) Management Company Limited | Households | 2021 |
| Old Rectory Hotel (Crostwick) Limited | Hospitality | 2007 |
| Old School Coffee Ltd | Hospitality | 2023 |
| Old Skool Pantry Limited | Hospitality | 2016 |
| Old Thorn Barn Ltd | Hospitality | 2010 |
| Old Town Consulting Limited | Professional & scientific | 2018 |
| Old Village Barrel Ltd | Hospitality | 2020 |
| Oldman Homes Limited | Construction | 1995 |
| Oldman Properties Limited | Construction | 2001 |
| Oldschoolvsnewschool Ltd | Information & communication | 2025 |
| Olethrion Omma Ltd | Professional & scientific | 2023 |
| OLH Properties Limited | Real estate | 2020 |
| OLI Impex Limited | Construction | 2009 |
| Oliromley Ltd | Wholesale & retail | 2023 |
| Oliva Verde Limited | Hospitality | 2026 |
| Olive HFE Ltd | Health & social care | 2024 |
| Olive Property Holdings Ltd | Real estate | 2025 |
| Olive Tree Holdings Ltd | Wholesale & retail | 2018 |
| Olive Tree Norwich Ltd | Hospitality | 2025 |
| Oliver & Hays Interiors Ltd | Professional & scientific | 2018 |
| Oliver and J Jewellery Limited | Wholesale & retail | 2015 |
| Oliver Bennett Electrical Ltd | Construction | 2021 |
| Oliver Court Limited | Health & social care | 2014 |
| Oliver's Craft Ltd | Wholesale & retail | 2025 |
| Oliverpeters Limited | Administrative & support | 2019 |
| OLL Events Ltd | Administrative & support | 2022 |
| Ollands Limited | Transport & logistics | 1997 |
| OLM Content Limited | Information & communication | 2018 |
| OLO International Ltd | Professional & scientific | 2020 |
| Olsen Recruitment Services Limited | Administrative & support | 2013 |
| Oltp Ltd | Information & communication | 2014 |
| Olympus Medical and Training Services Ltd. | Health & social care | 2023 |
| OMA Walter Ltd | Transport & logistics | 2015 |
| Omar Khan Surgical Services Limited | Health & social care | 2013 |
| Omar Ophthalmics Ltd | Health & social care | 2026 |
| OMC Enterprise Limited | Manufacturing | 2018 |
| Omci Ltd | Wholesale & retail | 2024 |
| OME Properties Ltd | Real estate | 2015 |
| Omega Beach Holdings Ltd | Administrative & support | 2020 |
| Omega Installations Ltd | Construction | 2020 |
| Omega Signalling Ltd. | Construction | 2022 |
| Omega Staffing Ltd | Administrative & support | 2019 |
| Omega Staffing Solutions Ltd | Administrative & support | 2019 |
| Omicron Engineering Limited | Manufacturing | 1984 |
| Ominira Health Limited | Wholesale & retail | 2015 |
| Omisphere Limited | Information & communication | 2026 |
| Omniathlete Holding Ltd | Financial services | 2022 |
| Omniathlete Ltd | Health & social care | 2021 |
| Omniathlete Sport Ltd | Health & social care | 2022 |
| OMOOSA2004 Limited | Health & social care | 2023 |
| ON Advice Limited | Construction | 2010 |
| ON Demand Fitness Ltd | Health & social care | 2020 |
| ON Guard Fencing Services Limited | Agriculture & fishing | 2024 |
| ON Reflection (East Anglia) Limited | Other services | 2007 |
| ON TAP Plumbing & Heating Limited | Construction | 2003 |
| ON the Go Automotive Ltd | Wholesale & retail | 2024 |
| ON the Stall City CIC | Wholesale & retail | 2021 |
| ON the Wonk Ltd | Administrative & support | 2012 |
| ON Top of Your Game Limited | Arts & recreation | 2013 |
| On-Board Scaffolding Ltd | Construction | 2018 |
| ON4CARE Limited | Administrative & support | 2018 |
| Onca Vets Ltd | Professional & scientific | 2019 |
| Once Upon a Doughnut Ltd | Wholesale & retail | 2020 |
| Oncon Products Limited | Wholesale & retail | 2020 |
| Ondemand ABC Ltd | Professional & scientific | 2023 |
| Ondemand CHH Ltd | Other services | 2023 |
| Ondemand EFG Ltd | Other services | 2023 |
| Ondemand XYZ Ltd | Administrative & support | 2021 |
| One Agency Group Limited | Financial services | 2016 |
| One Broker (Cambridge) Ltd | Financial services | 1973 |
| One Broker (Gdis) Ltd | Financial services | 2003 |
| One Broker Limited | Professional & scientific | 2009 |
| One Curious Dream Planning & Styling Limited | Other services | 2018 |
| One Day Store Ltd | Wholesale & retail | 2023 |
| One Five Zero Consultants Limited | Professional & scientific | 2025 |
| One Last Thing Ltd | Professional & scientific | 2014 |
| One Leisure Halifax Ltd | Hospitality | 2023 |
| One Million Roadsters Limited | Other services | 2019 |
| One Palace Street Management Limited | Households | 2017 |
| One Percent Property Ltd | Real estate | 2025 |
| One Planet Trading Ltd | Hospitality | 2009 |
| One Planning Ltd | Professional & scientific | 2011 |
| One Planning Solutions Limited | Professional & scientific | 2024 |
| One Provider Ltd. | Real estate | 2025 |
| One Sports Management Group Ltd | Arts & recreation | 2020 |
| One Stop Autos Norwich Limited | Wholesale & retail | 2026 |
| One Stop Business Advisory Services Limited | Real estate | 2021 |
| One Stop Italy Limited | Administrative & support | 2000 |
| One T NOT Two Ltd | Professional & scientific | 2020 |
| One to Relish Limited | Wholesale & retail | 2007 |
| One True Version (OTV) Limited | Information & communication | 2023 |
| One Way PCB Limited | Administrative & support | 2004 |