| NS Interiors Limited | Professional & scientific | 2026 |
| NS Services Solutions Ltd | Construction | 2020 |
| Nsnt Investments Ltd | Real estate | 2023 |
| NT Beauty & Laser Technology Ltd | Other services | 2024 |
| Nters Limited | Health & social care | 2019 |
| NTS Creative Ltd | Information & communication | 2012 |
| Nuamms Limited | Administrative & support | 2014 |
| Nudgematics Limited | Wholesale & retail | 2012 |
| Numbrfy Limited | Information & communication | 2023 |
| NUR Next GEN CIC | Arts & recreation | 2026 |
| NUT Basket Limited | Wholesale & retail | 2025 |
| NV Builders & Decorators Ltd | Construction | 2024 |
| NW Cleaning and Maintenance Ltd | Administrative & support | 2020 |
| NYK MS Ltd | Construction | 2022 |
| Nytlifeuk Ltd | Hospitality | 2019 |
| NYX Inn Hotels Limited | Hospitality | 2025 |
| O Picante Ltd | Hospitality | 2015 |
| O&A Awad Properties Limited | Real estate | 2024 |
| O-K Smart Home Technology Ltd | Construction | 2012 |
| Oak and Willow Flooring Ltd | Construction | 2019 |
| Oak and Willow Joinery Ltd | Construction | 2015 |
| Oak Knot Carpentry Ltd | Administrative & support | 2017 |
| Oakbridge Property Estates Ltd | Real estate | 2026 |
| Oakfield Decoration Ltd | Construction | 2014 |
| OB Home Management Limited | Real estate | 2017 |
| Obloj Construction Ltd | Construction | 2023 |
| Observe Communications Ltd | Manufacturing | 2014 |
| Ocean Discs Limited | Manufacturing | 2023 |
| OD Maintenance Ltd | Construction | 2018 |
| Odeon Tandoori Ltd | Hospitality | 2012 |
| Office Cleaning Services (UK) Limited | Administrative & support | 2012 |
| Oglu Property Ltd | Real estate | 2024 |
| OHG Safety Solutions Limited | Professional & scientific | 2009 |
| OJ Invest Limited | Construction | 2026 |
| OKB Attachments Limited | Wholesale & retail | 2017 |
| Olilen Ltd | Construction | 2019 |
| Olive Nest Ltd | Construction | 2025 |
| Olmi Consulting Limited | Real estate | 2018 |
| Olssea Limited | Wholesale & retail | 2024 |
| OM SAI Convenience Store Ltd | Wholesale & retail | 2019 |
| OM SAI Estate Ltd | Real estate | 2024 |
| Omdesignandbuild Ltd | Professional & scientific | 2024 |
| Omid Anaesthetic Services Limited | Health & social care | 2023 |
| Omni Tutoring (UK) Limited | Education | 2020 |
| Omran Ltd | Professional & scientific | 2019 |
| Omsera Ltd | Wholesale & retail | 2025 |
| Omus Limited | Construction | 2019 |
| ON Wood Ltd | Manufacturing | 2023 |
| One Art Ltd | Wholesale & retail | 2019 |
| One Care Collective Ltd | Health & social care | 2025 |
| One Perfect Solution Limited | Professional & scientific | 2010 |
| One UP Learning Ltd | Education | 2023 |
| One Way Global Mobility Services Ltd | Transport & logistics | 2024 |
| One-Stop Hospitality Solutions Ltd | Information & communication | 2025 |
| Oneleaf Wedding Decor Ltd | Hospitality | 2021 |
| Onestop MK Accountants Ltd | Professional & scientific | 2018 |
| Onetenuk Ltd | Wholesale & retail | 2025 |
| Onit Auto Management Ltd | Professional & scientific | 2026 |
| Only Horses Ltd | Information & communication | 2025 |
| Onset Way Technology Ltd | Information & communication | 2025 |
| Onsetway Limited | Construction | 2024 |
| Opal Electrics Limited | Energy | 2014 |
| Opallery Ltd | Other services | 2026 |
| Opan Limited | Hospitality | 2019 |
| Optical Techniques Ltd | Professional & scientific | 2023 |
| Optimum Business Supplies Ltd | Wholesale & retail | 2020 |
| Optimus Build Services Ltd | Construction | 2026 |
| Optimus Logic Ltd | Information & communication | 2025 |
| Options R Ltd | Information & communication | 2024 |
| Optml Logistics Limited | Transport & logistics | 2025 |
| Opulence ECS UK Limited | Wholesale & retail | 2025 |
| Orange Home Service Ltd | Wholesale & retail | 2026 |
| Orchid Fashion & Interior Design Limited | Real estate | 2008 |
| Orchidia Design Ltd | Professional & scientific | 2019 |
| Orhan Fast Food Ltd | Hospitality | 2026 |
| Oriental Gourmet Limited | Hospitality | 2017 |
| Orlene London Limited | Construction | 2026 |
| Ortana Media Group Limited | Administrative & support | 2013 |
| Orvist Limited | Hospitality | 2022 |
| Oscando Limited | Information & communication | 2022 |
| Osprey Brands Ltd | Wholesale & retail | 2021 |
| Oszami Developments Ltd | Information & communication | 2014 |
| Otario Ltd | Information & communication | 2025 |
| Otel Hospitality Solutions Ltd | Professional & scientific | 2021 |
| Otonomis Limited | Administrative & support | 2023 |
| OUD BOY Ltd | Wholesale & retail | 2025 |
| Ourcreativeedge Ltd | Arts & recreation | 2025 |
| Outsource Customer Services Ltd | Construction | 2023 |
| Ovenpride London Ltd | Wholesale & retail | 2025 |
| Over Road Limited | Construction | 2026 |
| Overseas Link International Ltd | Transport & logistics | 2020 |
| OVI Import&Export Limited | Wholesale & retail | 2017 |
| OVP Construction Limited | Construction | 2025 |
| Owen Fabrications Ltd | Manufacturing | 2001 |
| Owens Plant Services Limited | Wholesale & retail | 2003 |
| Oxytane Europe Ltd | Wholesale & retail | 2024 |
| Oxytane Poland Ltd | Wholesale & retail | 2024 |
| Oynx Collective Ltd | Financial services | 2024 |
| Oypbo Properties Ltd | Real estate | 2024 |
| OZA Supported Care Ltd | Health & social care | 2025 |