| North Wilts Bowls Club Limited | Arts & recreation | 1996 |
| North Wiltshire Taxi Rental Ltd | Administrative & support | 2022 |
| Northstar Automotive Ltd | Wholesale & retail | 2025 |
| Nortree Management Company Limited | Households | 1988 |
| NOT Just Ford Ltd | Wholesale & retail | 2024 |
| Notte Technologies Limited | Information & communication | 2022 |
| Notull Ltd | Information & communication | 2025 |
| Nova Modus Limited | Professional & scientific | 2011 |
| Nova Property and Consulting Ltd | Professional & scientific | 2023 |
| Novakeep Ltd | Information & communication | 2009 |
| Novergy Devco 2 Ltd | Professional & scientific | 2020 |
| Novergy Ltd | Professional & scientific | 2018 |
| NP Interim Limited | Professional & scientific | 2008 |
| NPJ Lettings Limited | Real estate | 2026 |
| NRG Marketing Consultancy Limited | Professional & scientific | 2023 |
| NSM Consultants & Training Limited | Information & communication | 2016 |
| NSN Engineering Services Limited | Professional & scientific | 2024 |
| Nsnyna Ltd | Professional & scientific | 2018 |
| Nsuku Solutions Ltd | Transport & logistics | 2024 |
| NU Cleaning Services Limited | Administrative & support | 2022 |
| NU FLU Property & Chimney Lining Services Limited | Construction | 1991 |
| Nueton Tech Ltd | Professional & scientific | 2024 |
| Nuga D'S Limited | Extraterritorial | 2024 |
| Nulectrics Ltd | Energy | 2017 |
| Nupower Ltd | Administrative & support | 2025 |
| Nutrition for Women Ltd | Health & social care | 2020 |
| NVL Solutions Ltd | Administrative & support | 2016 |
| NWB Facilities Management Ltd | Professional & scientific | 2023 |
| NÜ Legal Limited | Professional & scientific | 2017 |
| O and J Property (South West) Limited | Real estate | 2025 |
| O V Ventures Ltd | Transport & logistics | 2019 |
| O&J Building Limited | Construction | 2022 |
| O&J Electrical (Property) Services Ltd | Administrative & support | 2013 |
| O'Shea Consultants Limited | Administrative & support | 2016 |
| Oak Tree Boarding Kennels Limited | Other services | 2018 |
| Oak/Hardwoods Trading UK Limited | Wholesale & retail | 2019 |
| Oakbourne Construction Limited | Administrative & support | 1981 |
| Oakbridge Management System Specialists Ltd | Professional & scientific | 2023 |
| Oakhouse Foods Wessex Limited | Hospitality | 2017 |
| Oakleaf Consulting Ltd | Professional & scientific | 2015 |
| Oakleigh Acres Limited | Construction | 1977 |
| Oakline Interiors Ltd | Construction | 2025 |
| OAM Group Limited | Professional & scientific | 2024 |
| Oars PTY Ltd | Hospitality | 2019 |
| Oatlands Consulting Limited | Agriculture & fishing | 2022 |
| Obara Limited | Professional & scientific | 2009 |
| Oceansafe Medical Ltd | Health & social care | 2025 |
| OCP Services Ltd | Financial services | 2018 |
| OCR International Limited | Information & communication | 2018 |
| Octopus Films Limited | Information & communication | 2002 |
| Odette Nelson Limited | Health & social care | 2014 |
| Odin LLC Ltd | Financial services | 2024 |
| Odlum's Construction & Development Services Ltd | Energy | 2025 |
| OEM Transport Ltd | Transport & logistics | 2023 |
| OFF Grid Camp Ltd | Hospitality | 2021 |
| OFF the Hook Copywriting Ltd | Professional & scientific | 2021 |
| Offset Ltd | Other services | 2021 |
| Offshore Consulting Ltd | Professional & scientific | 2005 |
| OJU IT Services Limited | Administrative & support | 2012 |
| Oldland Electrical Services Limited | Construction | 2003 |
| Oldland M & E Services Ltd | Construction | 2014 |
| Oliv Homeware Ltd | Manufacturing | 2022 |
| Oliver's Electrical Limited | Construction | 2015 |
| OM Automation Limited | Professional & scientific | 2019 |
| Omarch Ltd | Extraterritorial | 2025 |
| Omnigov Limited | Professional & scientific | 2017 |
| Ondervinden Ltd | Arts & recreation | 2018 |
| One 77 Mortgages Limited | Financial services | 2010 |
| One Bird Ltd | Administrative & support | 2017 |
| One Show More Limited | Manufacturing | 2024 |
| One Stop Morris Shop Ltd. | Manufacturing | 2016 |
| One Thought Limited | Other services | 2010 |
| Onevast Limited | Administrative & support | 2014 |
| Onevision Trading Limited | Wholesale & retail | 2015 |
| Onslow Boyd Venture Capital Ltd. | Professional & scientific | 1897 |
| Opcw Holdings Limited | Manufacturing | 2018 |
| Opela Ltd | Financial services | 2023 |
| Open Learning Limited | Education | 2016 |
| Open Plan MAN Design Ltd | Construction | 2019 |
| Openda Limited | Information & communication | 1997 |
| Optimum Environment Ltd | Information & communication | 1998 |
| Opus 10 Limited | Information & communication | 1999 |
| Opus Group Holdings Limited | Extraterritorial | 2008 |
| Opus Healthcare Ltd. | Extraterritorial | 2003 |
| Oracle Hairdressing Limited | Other services | 2010 |
| Oracle Investments (Bath) Limited | Real estate | 2021 |
| Oram Home Improvements Limited | Construction | 2015 |
| Orange Tree Estates Limited | Real estate | 1997 |
| Orca Bay Ltd | Administrative & support | 2007 |
| Orchard House Veterinary Centres Limited | Professional & scientific | 2003 |
| Orchid Fashion Boutique Limited | Wholesale & retail | 2013 |
| Orchid Ridge Ltd | Professional & scientific | 2011 |
| Orderflow Ltd. | Information & communication | 2009 |
| Oria E-Commerce Ltd | Wholesale & retail | 2025 |
| Oriel Systems Limited | Information & communication | 1984 |
| Origin Rural Ltd | Professional & scientific | 2021 |
| ORIGIN8 South West Limited | Financial services | 2025 |
| Orrin Finance Ltd | Professional & scientific | 2024 |
| Oscar Stringer Limited | Education | 2005 |
| Oshine Ltd | Real estate | 2025 |