| Ntam Investments Limited | Real estate | 2025 |
| NTH Accountants Ltd | Professional & scientific | 2024 |
| Ntrl Aesthetics Ltd | Health & social care | 2024 |
| NU ME Salons Limited | Other services | 2023 |
| Nuga Golf UK Ltd | Professional & scientific | 2023 |
| Nuha Connections (UK) Ltd | Transport & logistics | 2014 |
| Nullix Ltd | Manufacturing | 2024 |
| Number 11 Group Limited | Wholesale & retail | 2022 |
| Nurasoft International Limited | Health & social care | 2015 |
| Nurturing Your Needs (NYN) CIC | Information & communication | 2019 |
| Nutcases Studio Limited | Arts & recreation | 2025 |
| Nutrinity Health Limited | Health & social care | 2018 |
| Nutrition Advice for Health Community Interest Company | Health & social care | 2014 |
| NV Travel Group Ltd | Administrative & support | 2019 |
| NVG Construction Ltd | Construction | 2024 |
| NVJ Associates Limited | Health & social care | 2019 |
| NWK Construction Ltd | Construction | 2019 |
| NWP Properties Limited | Administrative & support | 2017 |
| Nyemeka Limited | Health & social care | 2023 |
| O & H Power Solutions Ltd | Administrative & support | 2025 |
| O B Contracts Ltd | Professional & scientific | 2016 |
| O Stone (UK) Ltd | Manufacturing | 2014 |
| O&T Concept Limited | Other services | 2017 |
| O3 Capital UK Limited | Extraterritorial | 2022 |
| Oaasis Ltd | Health & social care | 2023 |
| Oactech Solutions Ltd | Information & communication | 2022 |
| Oak Carpentry Ltd | Construction | 2020 |
| Oak Lodge Property Investments Ltd | Real estate | 2024 |
| Oaklands Forest Investments Limited | Professional & scientific | 2025 |
| Oakley Community Services Limited | Administrative & support | 2025 |
| Oakroft Limited | Information & communication | 1998 |
| Oakside Court Management Association Limited | Households | 1969 |
| Oasis Capital Holdings Limited | Financial services | 2025 |
| OBA Engineering Limited | Professional & scientific | 2015 |
| Obad Properties Limited | Real estate | 2025 |
| Obatech UK Ltd | Wholesale & retail | 2024 |
| Obirin Africa Ltd | Education | 2020 |
| Obonna Ltd | Health & social care | 2026 |
| Obsidian Souls Tattoo Ltd | Arts & recreation | 2026 |
| Obsidian Universe Limited | Professional & scientific | 2026 |
| Occasions Cake Studio Limited | Hospitality | 2002 |
| Occhealthnet.Org Ltd | Health & social care | 2012 |
| Ocean Care Group Limited | Health & social care | 2019 |
| Ocean Care Residence Limited | Health & social care | 2025 |
| Ocean Mint (UK) Limited | Manufacturing | 2019 |
| Ocee the African Limited | Wholesale & retail | 2023 |
| OCJ Network Ltd | Information & communication | 2019 |
| Ocland Homes Limited | Health & social care | 2020 |
| OCT LOG Ltd | Transport & logistics | 2025 |
| Octav Home Renovations Ltd | Construction | 2026 |
| Odesti Care Services Ltd | Health & social care | 2023 |
| Odin Security Solutions Ltd | Construction | 2026 |
| OED Alliances Limited | Other services | 2019 |
| OG Electrical Solutions Ltd | Construction | 2026 |
| OG Halyard Limited | Wholesale & retail | 2021 |
| Ogle (UK) Ltd | Construction | 2013 |
| Ohana Parental Assessment Centre Limited | Health & social care | 2020 |
| Ohana Support Services Ltd | Health & social care | 2025 |
| Ohene Properties Ltd | Hospitality | 2026 |
| Ohlu Medicare Ltd | Health & social care | 2021 |
| Oiarm Nexus Ltd | Wholesale & retail | 2026 |
| Oilbase Ltd | Other services | 2026 |
| OJ Rail Limited | Construction | 2016 |
| OJO Healthcare Limited | Health & social care | 2022 |
| Ojuelegba Foods Ltd | Hospitality | 2024 |
| OK Parcel Ltd | Transport & logistics | 2021 |
| OKI Savehome Ltd | Hospitality | 2024 |
| Okitter Limited | Wholesale & retail | 2023 |
| Okogbe Services Limited | Construction | 2015 |
| OKY Trans Limited | Transport & logistics | 2010 |
| OLA AMT Ltd | Health & social care | 2023 |
| Old Mamooton Ltd | Transport & logistics | 2024 |
| Old Route 66 Transport Ltd | Transport & logistics | 2020 |
| Oldtrans Limited | Transport & logistics | 2017 |
| Oleg Garage Limited | Wholesale & retail | 2026 |
| Olihana Business Solutions Ltd | Professional & scientific | 2013 |
| Olive Green Therapy Ltd | Other services | 2023 |
| Olive Roots Limited | Hospitality | 2026 |
| Oliver Finn Limited | Administrative & support | 2025 |
| Olivia Jasmine Ltd. | Wholesale & retail | 2023 |
| Ollie Associates Limited | Professional & scientific | 2014 |
| OLU Courier & Logistics Limited | Transport & logistics | 2025 |
| Olubunmi Sanni Legal Consultancy Limited | Information & communication | 2023 |
| Olubunmi Sanni Ltd | Real estate | 2019 |
| Oluchigold Limited | Health & social care | 2024 |
| Oluwafayegbami Limited | Health & social care | 2023 |
| Olymp Fire Protection Ltd | Construction | 2021 |
| Omar Halal Meat and Groceries Ltd | Hospitality | 2024 |
| OMC Services Ltd | Transport & logistics | 2016 |
| Omega Supported Living Limited | Health & social care | 2025 |
| Omish Consulting Services Limited | Professional & scientific | 2014 |
| Omnialora Limited | Professional & scientific | 2026 |
| Omotii Limited | Health & social care | 2022 |
| Omtawy Ltd | Transport & logistics | 2019 |
| ON Point Mechanical Ltd | Construction | 2021 |
| ON Track Care Services Ltd | Health & social care | 2018 |
| On-Top Group Ltd | Wholesale & retail | 2018 |
| One Cloud Energy Limited | Information & communication | 2021 |
| One Day Wealth Limited | Financial services | 2019 |
| One Degree Skin Care Ltd | Wholesale & retail | 2026 |