| Nutzu Cladding Ltd | Construction | 2015 |
| Nuwave Design Limited | Professional & scientific | 2013 |
| NV Commercial Services Ltd | Transport & logistics | 2025 |
| NV Data Consulting Ltd | Information & communication | 2026 |
| Nvks Properties Ltd | Real estate | 2022 |
| Nvks Surfacing Ltd | Construction | 2026 |
| NW Supermarket Ltd | Wholesale & retail | 2019 |
| NW Tax and Advisory Limited | Professional & scientific | 2024 |
| Nwatson Limited | Real estate | 2012 |
| Nwlb Limited | Construction | 2013 |
| NX Technologies Ltd | Information & communication | 2019 |
| Nxcare Services Ltd | Health & social care | 2025 |
| NY Project Solutions Ltd | Professional & scientific | 2025 |
| Nyamah Investments Limited | Financial services | 2021 |
| Nyang Flowers Limited | Wholesale & retail | 2022 |
| Nyaya UK Ltd | Information & communication | 2022 |
| NYD Investment Limited | Real estate | 2015 |
| Nyna Tech Ltd | Information & communication | 2025 |
| Nytram IT Solutions Ltd | Administrative & support | 2017 |
| NZ FX Ltd | Information & communication | 2023 |
| NZ Osteopathy Sports Injury and Personal Training Ltd | Health & social care | 2019 |
| O & L Freeholds Limited | Real estate | 2006 |
| O'B Electrical Limited | Construction | 2016 |
| O'Connor Medical Limited | Health & social care | 2010 |
| O'Dea Properties Limited | Real estate | 2010 |
| O'Hanlon Consulting Limited | Professional & scientific | 2014 |
| O'Hara Group Limited | Extraterritorial | 2017 |
| O'Hara Legal Ltd | Professional & scientific | 2026 |
| O'Malley Haulage Limited | Transport & logistics | 2005 |
| O'Malley Limited | Extraterritorial | 2019 |
| O'Malley Management Limited | Administrative & support | 2013 |
| O'Malley Plant Services Limited | Administrative & support | 2013 |
| O'Neill Advanced Consulting Ltd | Professional & scientific | 2014 |
| O'Neill Private Finance Ltd | Financial services | 2008 |
| O'Reilly Mechanical Services Limited | Construction | 2018 |
| O'Sullivan Education Consulting Limited | Education | 2019 |
| O.Basha Construction Ltd | Construction | 2022 |
| O.E.M.K Solutions Ltd | Real estate | 2025 |
| O2R Ltd | Wholesale & retail | 2020 |
| OA IT Limited | Information & communication | 2026 |
| Oak Artisans Limited | Wholesale & retail | 2017 |
| Oak Court Northwood Limited | Construction | 2023 |
| Oak Court Northwood Residents Association Limited | Households | 1999 |
| Oak Court Residents Limited | Households | 1994 |
| Oak Financial Services Limited | Financial services | 2006 |
| Oak Nests Private Limited | Real estate | 2024 |
| Oak Park Estates Limited | Real estate | 2016 |
| Oak Property Solutions Ltd | Real estate | 2011 |
| Oak Tree Court (HA2) Management Company Limited | Households | 2008 |
| Oak Tree Gardens (ST Albans) Management Company Limited | Households | 2018 |
| Oakbank Management Company Limited(The) | Households | 1977 |
| Oakbridge Investments Ltd | Real estate | 2025 |
| Oakdene Close Management Limited | Households | 1981 |
| Oakes Business Consulting Limited | Information & communication | 2002 |
| Oakhurst Place Residents Limited | Households | 1999 |
| Oakhurst Property Developments (Lowndes Square NO.2) Limited | Construction | 2005 |
| Oakingham Estates Limited | Households | 2017 |
| Oakingham Islington Limited | Households | 2017 |
| Oaklands (Watford) Amenities Association Limited | Households | 1960 |
| Oakmont Grove Ltd | Real estate | 2023 |
| Oakro Construction Ltd | Manufacturing | 2019 |
| Oaksedge Limited | Administrative & support | 1996 |
| Oakshield Limited | Construction | 2007 |
| Oakwood Bespoke Interiors Limited | Manufacturing | 2025 |
| Oakwood Care Operations Ltd | Administrative & support | 2023 |
| Oakwood Care Property Ltd | Real estate | 2023 |
| Oana Hair Studio Ltd | Other services | 2019 |
| Oaservices Ltd | Health & social care | 2026 |
| Oasis Tools Ltd | Extraterritorial | 2012 |
| OBE Consultants Limited | Information & communication | 2005 |
| Object Support Ltd | Information & communication | 2021 |
| Oborne Woodhams Lettings Ltd | Real estate | 2020 |
| Obrapa Afro Shop Ltd | Wholesale & retail | 2019 |
| OBT Chukso Ltd | Construction | 2012 |
| OCA Holdings Ltd | Real estate | 2019 |
| Occurro Consulting Ltd | Professional & scientific | 2011 |
| Ocean Freight Logistics Ltd | Transport & logistics | 2025 |
| Ocean Recovery and Wellness Centre Ltd | Health & social care | 2014 |
| Oceanic Technologies Limited | Information & communication | 2017 |
| Oceanmoon Ltd | Information & communication | 2023 |
| OCG Finance Ltd | Financial services | 2020 |
| Ochi Management Limited | Professional & scientific | 2010 |
| Octagon Facilities Management Benefits Ltd | Administrative & support | 2020 |
| Octavian Business Consultancy Limited | Professional & scientific | 2016 |
| Octavit Health Products Ltd | Wholesale & retail | 2026 |
| October House Holdings Ltd | Financial services | 2020 |
| Octopus Automotive Ltd | Wholesale & retail | 2018 |
| Octopus Roxy Group Limited | Construction | 2024 |
| Oculise Ltd | Health & social care | 2015 |
| Odai Immigration Consultants Ltd | Administrative & support | 2023 |
| Oddfellows PUB Ltd | Hospitality | 2025 |
| Odin Marketing Services Limited | Information & communication | 2022 |
| ODO Marketing Ltd | Wholesale & retail | 2019 |
| Odoor Control Ltd | Manufacturing | 2026 |
| OEL Nationwide Payroll Limited | Professional & scientific | 2026 |
| Office Partners Ltd | Professional & scientific | 2018 |
| Official Divine Events Ltd | Hospitality | 2021 |
| OFG Consulting Limited | Professional & scientific | 2025 |
| OFM Automotive Ltd | Wholesale & retail | 2023 |
| OFM Performance Ltd | Wholesale & retail | 2026 |