| Nura Aesthetics Limited | Wholesale & retail | 2025 |
| Nursery Field (Thorpe Le-Soken) Management Company Limited | Households | 2023 |
| Nurturance AI Ltd | Professional & scientific | 2023 |
| Nurz Ltd | Health & social care | 2019 |
| Nustone Group Ltd | Financial services | 2025 |
| Nustone Patios Ltd | Wholesale & retail | 2025 |
| Nutek (UK) Ltd | Other services | 1999 |
| Nutek IT Ltd | Information & communication | 2007 |
| Nuto X Projects Ltd | Hospitality | 2025 |
| Nutramax Ltd | Hospitality | 2022 |
| Nutrex Ltd | Health & social care | 2021 |
| Nutricol Ltd | Wholesale & retail | 2008 |
| NVT Care Services Ltd | Health & social care | 2013 |
| Nyams Home Improvements Ltd | Administrative & support | 2016 |
| Nyatundo Ltd | Health & social care | 2021 |
| Nycelink Ltd | Real estate | 2025 |
| NYD Property Ltd | Real estate | 2020 |
| Nymk Consultancy Ltd | Professional & scientific | 2024 |
| O & L Properties Limited | Real estate | 2021 |
| O J Plastering Limited | Construction | 2019 |
| O Summers Coaching Ltd | Administrative & support | 2024 |
| O&E Pro Limited | Information & communication | 2019 |
| O&J Capital Management Limited | Professional & scientific | 2018 |
| O&L Fishing Limited | Manufacturing | 2023 |
| O&M Homes Limited | Real estate | 2018 |
| O&M Pension Solutions Limited | Financial services | 2014 |
| O'Connell Consultancy Services Ltd | Professional & scientific | 2020 |
| O'Hara Drylining (East) Limited | Construction | 2021 |
| O'Hara Plastering and Drylining Limited | Construction | 2005 |
| O'Hare Installations Limited | Construction | 2025 |
| O'Tarigi Ltd | Wholesale & retail | 2021 |
| O.N.E Choice Tiling Ltd | Construction | 2018 |
| O.T Waste Removal Ltd | Water & waste | 2026 |
| O2 Business Solutions Limited | Financial services | 1998 |
| O2 Management Solutions Limited | Financial services | 2000 |
| O2 Software Solutions Limited | Information & communication | 1998 |
| OAB Developments Limited | Construction | 2016 |
| OAB Properties Limited | Real estate | 2023 |
| OAB Technologies Ltd | Information & communication | 2018 |
| OAC Development Ltd | Construction | 2015 |
| Oak & Legacy Ltd. | Professional & scientific | 2024 |
| Oak Design and Construction Limited | Administrative & support | 2022 |
| Oak House East Anglia Limited | Real estate | 2010 |
| Oak Tree Gardens (Colchester) Management Company Limited | Real estate | 2010 |
| Oak Tree Place Management Company Limited | Households | 2022 |
| Oak Valley IT Ltd | Information & communication | 2025 |
| Oak View Developments Limited | Extraterritorial | 2017 |
| Oak View Landscapes Limited | Administrative & support | 2004 |
| Oak View Limited | Real estate | 2012 |
| Oak View Properties Anglia Limited | Real estate | 2025 |
| Oak&Kapok Limited | Hospitality | 2019 |
| Oakbourne Management Company Limited | Households | 2017 |
| Oakdene Gate Management Ltd | Real estate | 2013 |
| Oaken Royd Croft (Properties) Limited | Households | 2011 |
| Oakenwoods Drywall Limited | Construction | 2023 |
| Oakenwoods Group Ltd | Construction | 2018 |
| Oakenwoods Interiors Ltd | Construction | 2023 |
| Oakenwoods Joinery Ltd | Manufacturing | 2023 |
| Oakfield Mews Limited | Health & social care | 2020 |
| Oakfield Quality Homecare Limited | Health & social care | 2015 |
| Oakheart Bury Ltd | Real estate | 2023 |
| Oakheart Chelmsford Ltd | Real estate | 2024 |
| Oakheart Colchester Ltd | Real estate | 2021 |
| Oakheart Investments Ltd | Real estate | 2024 |
| Oakheart Land Ltd | Real estate | 2022 |
| Oakheart Lettings Ltd | Real estate | 2020 |
| Oakheart Mersea Ltd | Real estate | 2023 |
| Oakheart New Homes Ltd | Real estate | 2024 |
| Oakheart Property (Ipswich) Ltd | Real estate | 2025 |
| Oakheart Property Ltd | Real estate | 2020 |
| Oakheart Sudbury Ltd | Real estate | 2021 |
| Oaklands Court (Cambridge Road) Freehold Limited | Households | 2005 |
| Oaklands Management Company (Parsons Heath) Limited | Households | 2019 |
| Oaklands Management Company (Tollesbury) Limited | Real estate | 2020 |
| Oaklea Montessori Community Interest Company | Administrative & support | 2008 |
| Oakley Contracts Ltd | Construction | 2016 |
| Oakley Protection Services Limited | Financial services | 2022 |
| Oakley Wine Agencies Limited | Wholesale & retail | 2007 |
| Oakline Solutions Ltd | Professional & scientific | 2026 |
| Oakridge Construction East Anglia Limited | Construction | 2020 |
| Oakstock Ltd | Administrative & support | 2019 |
| Oaksworld Limited | Wholesale & retail | 2017 |
| Oakview Drive (Harlow) Management Company Limited | Households | 2023 |
| Oakview Import Sales Ltd | Wholesale & retail | 2026 |
| Oakview Motors Ltd | Wholesale & retail | 2019 |
| Oakville Property Ltd | Real estate | 2022 |
| Oakwood Carpentry Services Ltd | Administrative & support | 2016 |
| Oakwood Cars Limited | Wholesale & retail | 2025 |
| Oakwood Consultancy Limited | Professional & scientific | 2015 |
| Oakwood Meadows (Colchester) Residents Management Company Limited | Households | 2016 |
| Oasis & Bird Limited | Professional & scientific | 2025 |
| Oasis Court Limited | Real estate | 1999 |
| OAT QA Ltd | Administrative & support | 2011 |
| OB Mirza Estates Ltd | Real estate | 2026 |
| Obesity East Limited | Health & social care | 2021 |
| OBI Innovations Limited | Professional & scientific | 2026 |
| Object Resource Ltd | Information & communication | 2019 |
| Oblako Limited | Professional & scientific | 2012 |
| Obrita Ltd | Wholesale & retail | 2025 |
| Obsession Reptiles Ltd | Other services | 2024 |