| Nor-Cote International Limited | Manufacturing | 1993 |
| North Harbour Trustees Limited | Administrative & support | 2005 |
| North South Finance Limited | Financial services | 2000 |
| North West London Builders Limited | Construction | 2017 |
| Northface Connections Limited | Information & communication | 1989 |
| Northover & Co Accountants Ltd | Professional & scientific | 2015 |
| Northumbria Rail Limited | Manufacturing | 2003 |
| Northytv Limited | Information & communication | 2017 |
| Norton Medical Limited | Administrative & support | 2015 |
| Norton Precision Limited | Manufacturing | 1997 |
| Nosac Limited | Extraterritorial | 2017 |
| Nova Creative Solutions Ltd | Information & communication | 2020 |
| NOW Fate Ltd | Wholesale & retail | 2026 |
| NQ2 Manchester Limited | Hospitality | 2019 |
| NRG Surveying Limited | Professional & scientific | 2014 |
| NRS Surveying Limited | Professional & scientific | 2012 |
| NRS Trauma Solutions Ltd | Education | 2026 |
| NS Site Fabrication Ltd | Manufacturing | 2019 |
| NSF Media Limited | Manufacturing | 2024 |
| NSK Car Sales Ltd | Wholesale & retail | 2023 |
| NST Agencies UK Ltd | Transport & logistics | 2026 |
| NTM Excel Limited | Construction | 2008 |
| Nucleus Marketing Ltd | Administrative & support | 2004 |
| Nuday Property Managers Ltd | Real estate | 2022 |
| Number 18 Tdmp Holding Limited | Financial services | 2024 |
| Number Eight Justice Walk Ltd | Real estate | 2006 |
| Numeric Holdings Limited | Real estate | 2016 |
| Nurtured Oaks Limited | Professional & scientific | 2019 |
| Nuthatch Property Ltd | Construction | 2024 |
| NWD Ltd | Construction | 2022 |
| Nyland Partners Limited | Wholesale & retail | 2021 |
| Nymble Consulting Ltd | Professional & scientific | 2020 |
| NZC Research Ltd | Professional & scientific | 2021 |
| O & M Contracting (South West) Ltd | Professional & scientific | 2022 |
| O Edwards Ltd | Wholesale & retail | 2020 |
| O&H Property Services Ltd | Construction | 2020 |
| OA Freight Limited | Transport & logistics | 2018 |
| OA Interior Decor Ltd | Construction | 2025 |
| OA Pharma Ltd | Health & social care | 2021 |
| Oak Associates (UK) Limited | Professional & scientific | 2014 |
| Oak Telecoms & Rigging Services Ltd | Construction | 2023 |
| Oakhaven Associates Limited | Real estate | 2021 |
| Oakley & Norman Limited | Wholesale & retail | 2018 |
| Oakley and Norman Tiles Limited | Wholesale & retail | 2020 |
| Oakmount Autos Limited | Wholesale & retail | 2002 |
| Oakmount Tdmp Holding Limited | Financial services | 2022 |
| Oaktree Education Schools Ltd | Education | 2026 |
| Oaktree Education Services Limited | Education | 2022 |
| Oaktree Education Services North West Ltd | Education | 2026 |
| Oaktree Support Services Holdings Ltd | Financial services | 2025 |
| Oakwood Finance Limited | Professional & scientific | 2007 |
| Oase (UK) Limited | Manufacturing | 1993 |
| OBC (Southern) Limited | Construction | 2025 |
| Observeon Limited | Professional & scientific | 2025 |
| Ocean Art (Southern) Limited | Administrative & support | 2003 |
| Ocean Census Limited | Information & communication | 2023 |
| Ocean International Limited | Extraterritorial | 2023 |
| Ocean Trident Ltd | Information & communication | 2018 |
| Ocean Waters Investment Properties Ltd | Real estate | 2026 |
| Ocean World Travel Limited | Administrative & support | 2021 |
| Oceanside Logistics Limited | Transport & logistics | 2011 |
| Octagon UK Limited | Professional & scientific | 1990 |
| OCW Advisory Ltd | Professional & scientific | 2026 |
| ODE & RAE Limited | Wholesale & retail | 2017 |
| Odfjell RIG V Ltd | Mining & quarrying | 2018 |
| Offshore OPS Ltd | Wholesale & retail | 2012 |
| Offshore Wind Network Limited | Professional & scientific | 2023 |
| Offspring Estates Ltd | Financial services | 2020 |
| Ogbebor E B Property Limited | Real estate | 2022 |
| Ogden Enterprise Limited | Financial services | 2018 |
| OHM LAB Ltd | Manufacturing | 2025 |
| Oidi Ltd | Education | 2015 |
| OJM Yachts Limited | Wholesale & retail | 2023 |
| OJP Holdco Ltd | Financial services | 2024 |
| OJS Plumb & Heat Ltd | Construction | 2023 |
| OK International Limited | Manufacturing | 1977 |
| OKH Limited | Administrative & support | 2018 |
| Old Goaled and Black Limited | Financial services | 2014 |
| Olivia Todd Limited | Other services | 2016 |
| OLM Haulage Ltd | Transport & logistics | 2026 |
| Olson Property Developments Limited | Real estate | 2003 |
| Olutopsy Limited | Administrative & support | 2009 |
| OM Dhanvi Ltd | Wholesale & retail | 2026 |
| OM Prabhu Ltd | Wholesale & retail | 2023 |
| OM Shree Hari Ltd | Real estate | 2025 |
| OMG Hair & Beauty Limited | Administrative & support | 2006 |
| Omij Limited | Hospitality | 2025 |
| Omni Games Studio Ltd | Information & communication | 2025 |
| Omnium Action Surveys Ltd | Professional & scientific | 2015 |
| ON Point Detailing Southampton Limited | Administrative & support | 2022 |
| ON Site Paint Spraying Ltd | Construction | 2024 |
| ON the Move Taxis Limited | Transport & logistics | 2024 |
| ON the Water Limited | Administrative & support | 2015 |
| One Community Eastleigh | Health & social care | 1995 |
| One Feeds Two Limited | Professional & scientific | 2014 |
| One Horizon Group Limited | Professional & scientific | 2004 |
| One Sight Group Limited | Financial services | 2021 |
| One Sightsolutions Limited | Information & communication | 2008 |
| One Signs Limited | Real estate | 2026 |
| One Two Tree Contracting Limited | Agriculture & fishing | 2025 |