| Ntrusted Estates Limited | Professional & scientific | 2018 |
| Nu-Clean DRY Cleaners Limited | Other services | 2014 |
| Nucleus Clyde Acquisition Limited | Financial services | 2022 |
| Nucleus Financial Limited | Financial services | 2005 |
| Nucleus Financial Platforms Limited | Professional & scientific | 2006 |
| Nucleus Financial Services Limited | Financial services | 2005 |
| Nucleus Group Services Limited | Professional & scientific | 1990 |
| Number 11 Consultants Limited | Professional & scientific | 2023 |
| Number 2 Holders Road Management Limited | Households | 2000 |
| Numbertel Ltd | Information & communication | 2009 |
| Numeric Accounting Limited | Professional & scientific | 2000 |
| Numeric Audit Ltd | Professional & scientific | 2007 |
| Numeric Group Holdings Limited | Financial services | 2024 |
| Numerical Dynamics Limited | Information & communication | 2020 |
| Nunton Dairy Management Company Limited | Administrative & support | 2002 |
| NUP END Green Management Company Limited | Real estate | 2018 |
| Nutmeg Property Limited | Professional & scientific | 2007 |
| Nuts and Bolts Training Limited | Administrative & support | 2016 |
| Nutshell Portions Limited | Manufacturing | 2025 |
| Nwful Ltd | Transport & logistics | 2026 |
| NWS Ltd | Administrative & support | 2008 |
| O Golden Services Ltd | Information & communication | 2022 |
| O&E Carpentry & Joinery Limited | Construction | 2008 |
| O'Driscoll Sports Equipment Ltd | Wholesale & retail | 2013 |
| O'Marah Construction Limited | Construction | 2011 |
| O.D.A. Limited | Hospitality | 1987 |
| Oades Consultancy Ltd | Professional & scientific | 2025 |
| Oak ASH Consultancy Ltd | Financial services | 2024 |
| Oak Direct Limited | Wholesale & retail | 2016 |
| Oak Drive Owners Ltd | Households | 2024 |
| Oak Leaf Developments (SW) Limited | Construction | 2018 |
| Oak Park (Liphook) Management Company Limited | Households | 2016 |
| Oak Tree Court ST Mellons Management Company Limited | Households | 2006 |
| Oakdawn Limited | Real estate | 1975 |
| Oakhill Gardens (Swanmore) Management Company Limited | Households | 2016 |
| Oakhill Property Management Limited | Real estate | 2014 |
| Oakhurst Blinds Limited | Manufacturing | 2003 |
| Oaklands Investments Limited | Real estate | 1984 |
| Oakleaf Services Limited | Construction | 2022 |
| Oakleigh Mews Swindon Apartments Management Company Limited | Households | 2004 |
| Oakley Property Partnership Ltd | Real estate | 2023 |
| Oakridge Consulting Limited | Professional & scientific | 2022 |
| Oakwood Contractors Ltd | Construction | 2020 |
| Oakwood Gate (Bampton) Management Company Limited | Households | 2016 |
| Oakwood Grove (Alderholt) Management Limited | Households | 2024 |
| Oasisairbridge Limited | Professional & scientific | 2021 |
| OB Heating and Plumbing Ltd | Construction | 2025 |
| Obake Studio Limited | Information & communication | 2025 |
| Objective Video Ltd | Information & communication | 2013 |
| Oblongical Limited | Real estate | 2020 |
| Obsidyan Limited | Professional & scientific | 2021 |
| Ocean Footprint Ltd | Manufacturing | 2016 |
| Ocean Footprint Solutions Ltd | Manufacturing | 2025 |
| Ocean Solar Ltd | Construction | 2012 |
| Oceanic Developments Ltd | Construction | 2014 |
| Ockenden Tree Services Limited | Agriculture & fishing | 2018 |
| Ockford Park (Godalming) Management Company Limited | Households | 2019 |
| Octadale Limited | Other services | 1994 |
| Octavia House Limited | Households | 1999 |
| Octavus Developments Limited | Construction | 2013 |
| Octavus Properties LLP | | 2009 |
| Odin Properties Ltd | Real estate | 2020 |
| Odinflex Ltd | Wholesale & retail | 2024 |
| ODN Consulting Limited | Professional & scientific | 2024 |
| Odstock Medical Limited | Health & social care | 2005 |
| OE Creativity Ltd | Professional & scientific | 2020 |
| OFF Limit Engineering Limited | Professional & scientific | 2008 |
| OFF the Table Limited | Extraterritorial | 2026 |
| Offbeat Wines Limited | Manufacturing | 2019 |
| Offcamping Ltd | Manufacturing | 2025 |
| Office Connect Recruitment Ltd | Administrative & support | 2019 |
| Ogwi Limited | Information & communication | 2022 |
| OHJ Bathrooms Limited | Construction | 2014 |
| OIL and GAS Machinery Consultants Limited | Professional & scientific | 2023 |
| OJA Global Ltd | Information & communication | 2018 |
| Oktopus Limited | Professional & scientific | 2016 |
| Olaji Limited | Wholesale & retail | 2011 |
| Old Alresford Logs Limited | Wholesale & retail | 2023 |
| Old Forge (Chilmark) Management Company Limited | Households | 2005 |
| Old Granary Court (Amesbury) Management Limited | Households | 1994 |
| Old House Management Company (Salisbury) Limited(The) | Households | 1988 |
| Old Inn Allington Limited | Hospitality | 2013 |
| Old Mill House (Harnham) Freehold Limited | Households | 2016 |
| Old PYE House Limited | Households | 1995 |
| Old Sarum Developments Limited | Construction | 2024 |
| Old Sarum Nursery | Education | 2012 |
| Old Sarum Office Developments Limited | Professional & scientific | 2005 |
| Old Sarum Stadium Limited | Arts & recreation | 1993 |
| Old Sarum Tattoo Limited | Other services | 2021 |
| Old School Close Freehold Ltd | Households | 2024 |
| Old Stour Broilers Limited | Agriculture & fishing | 2018 |
| Old Stour Poultry Limited | Agriculture & fishing | 2015 |
| Old Times Catering Ltd | Manufacturing | 2023 |
| Oldfield Meadow Management Company Limited | Households | 2019 |
| Olive Morris House (Brixton) Management Company Limited | Households | 2020 |
| Ollie Quinn UK Limited | Wholesale & retail | 2013 |
| Olmez Catering Limited | Hospitality | 2019 |
| Olra Activewear Ltd | Wholesale & retail | 2022 |
| Olski Ltd | Transport & logistics | 2025 |
| Omaswar Investments Limited | Real estate | 1961 |