| NRC CONSULTING2 Limited | Information & communication | 2015 |
| NS E Works Ltd | Information & communication | 2024 |
| Nshift Limited | Information & communication | 2015 |
| NSI Real Estate Limited | Real estate | 2020 |
| NSI Support Services Limited | Professional & scientific | 2002 |
| NSK Bearings Europe Limited | Manufacturing | 1974 |
| NSK Bearings Limited | Extraterritorial | 1987 |
| NSK Europe Limited | Professional & scientific | 1988 |
| NSK Precision UK Limited | Manufacturing | 2003 |
| NSK Steering Systems Europe (UK) Limited | Professional & scientific | 1999 |
| NSK Steering Systems Europe Limited | Manufacturing | 1994 |
| NSK Steering Systems UK Limited | Wholesale & retail | 2023 |
| NSK UK Limited | Wholesale & retail | 1988 |
| NT Carpentry Service Ltd | Construction | 2017 |
| NTB Investments Ltd | Real estate | 2026 |
| Nu-U Clinics Ltd | Health & social care | 2019 |
| Nubego Limited | Information & communication | 2014 |
| Nugen Homes Limited | Real estate | 2024 |
| NUH Media and Advertising Ltd | Administrative & support | 2018 |
| Number 1 Plate Supplies Limited | Manufacturing | 2026 |
| Number Scale Limited | Administrative & support | 2011 |
| Nunya Business Group Ltd | Wholesale & retail | 2025 |
| Nuraxi Limited | Professional & scientific | 2025 |
| Nureno Limited | Construction | 2019 |
| Nurture Properties Ltd | Real estate | 2022 |
| Nurturelife Tech Limited | Manufacturing | 2023 |
| Nutravita Limited | Wholesale & retail | 2014 |
| Nutrition Means Business Ltd | Professional & scientific | 2014 |
| Nuxeo Group Limited | Extraterritorial | 2017 |
| Nuxeo Limited | Extraterritorial | 2017 |
| NVS Design Limited | Professional & scientific | 2017 |
| Nylex Projects Limited | Construction | 2015 |
| Nysynergy Ltd. | Professional & scientific | 2009 |
| O J Building Consultants Limited | Professional & scientific | 2026 |
| O J Health & Safety Solutions Limited | Professional & scientific | 2007 |
| O P Hopkins Mechanical Engineering Services Limited | Construction | 2017 |
| O'Neill Modernmedia (OMM) Limited | Manufacturing | 2009 |
| O-Pharm Limited | Other services | 2020 |
| O.M.Turski Limited | Manufacturing | 2018 |
| Oairo Alliance Limited | Construction | 2016 |
| Oakford Homes (Arundel) Management Company Limited | Households | 2025 |
| Oakford Homes (Aylesbury) Management Company Limited | Households | 2026 |
| Oakingham Care Limited | Health & social care | 2017 |
| Oaklawn Consulting Limited | Professional & scientific | 2017 |
| Oakley Cars Ltd | Transport & logistics | 2019 |
| Oakley Heating & Plumbing Ltd | Construction | 2019 |
| Oakley Stables Livery Ltd | Agriculture & fishing | 2025 |
| Oakwood Care Ltd | Health & social care | 2023 |
| OBLONG3D Ltd | Information & communication | 2024 |
| Obsidian Commercial Development Ltd | Construction | 2023 |
| Obviously Group Limited | Information & communication | 2019 |
| Occuplay Ltd | Wholesale & retail | 2001 |
| Occuplay Rentals Ltd | Real estate | 2025 |
| Ocean Blue Colours Ltd | Hospitality | 2021 |
| Ocean Partners Holdings Limited | Wholesale & retail | 2004 |
| Ocean Partners Investments Limited | Administrative & support | 2006 |
| Ocean Partners UK Limited | Wholesale & retail | 2004 |
| Ocean Partners UK Trading Limited | Wholesale & retail | 2014 |
| Oceanpath Traders Ltd | Wholesale & retail | 2025 |
| Ocho London Ltd | Manufacturing | 2018 |
| Ockash Energy Limited | Professional & scientific | 2025 |
| Ockwells Manor Ltd | Real estate | 2024 |
| Ockwells Property Ltd | Real estate | 2011 |
| OCR Rally Limited | Manufacturing | 2023 |
| Octane Films Ltd | Information & communication | 2008 |
| Octane Power Services Ltd | Extraterritorial | 2025 |
| Odak Property Limited | Real estate | 2023 |
| Odatacy Network Ltd | Information & communication | 2024 |
| Odourlog Limited | Professional & scientific | 2025 |
| OFF the TAP Limited | Hospitality | 2017 |
| Office Answers Limited | Administrative & support | 2004 |
| Offone Ltd | Wholesale & retail | 2024 |
| OGB Trading Limited | Information & communication | 2008 |
| OH Beautiful Days Limited | Other services | 2019 |
| OH Event Management Ltd | Administrative & support | 2018 |
| Ohmylashuk Ltd | Wholesale & retail | 2018 |
| Ojaman Technologies Limited | Information & communication | 2025 |
| Ojumed Limited | Real estate | 2022 |
| Ojumed Pharma Limited | Professional & scientific | 2014 |
| Olafsky Limited | Wholesale & retail | 2024 |
| Old Bray Estate Planning Ltd | Financial services | 2012 |
| Old Bray Financial Limited | Financial services | 2012 |
| Old Convergence Pharmaceuticals Limited | Professional & scientific | 2010 |
| Old Court House (Kensington) Limited | Real estate | 1991 |
| Old Systems Limited | Information & communication | 1997 |
| Oldacres Estate Limited | Real estate | 2017 |
| Oldfield Lodge Medical Practice Limited | Health & social care | 2000 |
| Oldfield Lodge Partnership Limited | Health & social care | 2000 |
| Oldfield Lodge Property Holdings Limited | Health & social care | 2000 |
| Oldfields Properties Ltd | Construction | 2016 |
| Olive & Branch Properties Ltd | Real estate | 2025 |
| OLIVEDOG2020 Limited | Other services | 2020 |
| Olives Limited | Wholesale & retail | 2008 |
| Olympus 123 Limited | Financial services | 2020 |
| Olympus 456 Limited | Financial services | 2020 |
| Olympus 789 Limited | Financial services | 2020 |
| Olympus Recruitment Ltd | Administrative & support | 2020 |
| OM Consultancy Ltd. | Information & communication | 2015 |
| OM Investments Ltd | Real estate | 2017 |
| OMA Property Ltd | Real estate | 2016 |