| Nritya Limited | Public administration | 2025 |
| NSI Services Ltd | Construction | 2025 |
| NTC Group Limited | Real estate | 2024 |
| Ntutu Limited | Professional & scientific | 2014 |
| NU3 CIC | Professional & scientific | 2024 |
| Nubian Kweenwear Limited | Wholesale & retail | 2017 |
| Nullrabbit Limited | Professional & scientific | 2025 |
| Number 1 Scaffolding Ltd | Construction | 2025 |
| Number 8 Warham Road Management Company Limited | Households | 1982 |
| Nuri's Cafe Limited | Wholesale & retail | 2019 |
| Nuts Marine Ltd | Extraterritorial | 2023 |
| NVA One Ltd | Real estate | 2024 |
| NVH Investments & Developments Limited | Real estate | 2019 |
| Nvkn Limited | Health & social care | 2015 |
| Nwakaego Services Limited | Health & social care | 2023 |
| Nwsb Property Ltd | Real estate | 2025 |
| NXT Level Rigging Ltd | Construction | 2021 |
| Nyamminz Ltd | Hospitality | 2022 |
| Nzuri Property & Management Limited | Real estate | 2015 |
| O'Brien Investment Holdings Limited | Real estate | 2025 |
| O'Donnell Support Services Ltd | Professional & scientific | 2016 |
| O.I Catering Ltd | Hospitality | 2021 |
| O.S.T.C. Limited | Financial services | 2004 |
| O.T.M Films Ltd | Information & communication | 2012 |
| OA Property Services Limited | Construction | 2026 |
| Oadtrin Lodge Ltd | Households | 2014 |
| Oak Harrington Limited | Hospitality | 2013 |
| Oakdene Block Freehold Limited | Households | 2022 |
| Oakfarm Energy Ltd | Construction | 2026 |
| Oakfield (Shortlands Grove) Limited | Households | 1993 |
| Oakland Property Solutions Ltd | Construction | 2021 |
| Oakley Gardens Management Company Ltd | Real estate | 2008 |
| Oakley House Bromley Limited | Hospitality | 2022 |
| Oakmead Management Company (Number 1) Limited | Households | 1990 |
| Oakways Consult Limited | Construction | 2017 |
| Oast Court Farm Management Company Limited | Real estate | 2010 |
| OBA Global Ltd | Information & communication | 2025 |
| OBA Stiftung Ltd | Construction | 2023 |
| OBI Hair Limited | Other services | 2020 |
| OBI London Limited | Other services | 2022 |
| OBI Spaces Limited | Real estate | 2022 |
| Objective Rush Limited | Information & communication | 2020 |
| OC Ventures Ltd | Real estate | 2023 |
| Ocea International Limited | Wholesale & retail | 1999 |
| Ocean House (Three Bridges) RTM Company Limited | Real estate | 2019 |
| Oceanic Skyline Ltd | Real estate | 2021 |
| Oceanic View Limited | Information & communication | 2011 |
| Octa Bridges Holdco Limited | Financial services | 2023 |
| Octa Point Investments Limited | Real estate | 2023 |
| Octagon Nest Limited | Professional & scientific | 2012 |
| Octatec Limited | Hospitality | 1993 |
| October Court Management Limited | Households | 1976 |
| Octopus International Events Limited | Administrative & support | 2024 |
| Oddson Models Ltd | Information & communication | 2025 |
| Oduduwa Heritage Awards | Arts & recreation | 2025 |
| OE Book-Keeping and Accounts Ltd | Professional & scientific | 2011 |
| OFF Mode Ltd | Wholesale & retail | 2025 |
| Off-Grid Housing Solutions Ltd | Construction | 2024 |
| Ofstreet INT Ltd | Health & social care | 2010 |
| Ohmix Ltd | Construction | 2026 |
| Ohyah Store Ltd | Wholesale & retail | 2026 |
| Oilsearch Limited | Professional & scientific | 1994 |
| OJ Plumbing & Heating Services Limited | Construction | 2022 |
| OJH Services Ltd | Water & waste | 2026 |
| OJJ BAV Limited | Real estate | 2026 |
| OJL Electrical Contractors Limited | Construction | 2026 |
| OK Properties (London) Ltd | Real estate | 2018 |
| OK Propoerties Management Ltd | Real estate | 2025 |
| Okawanyi-Agila Property and Services Ltd | Real estate | 2026 |
| Okie Fokie Ltd | Professional & scientific | 2015 |
| OKIN1 Limited | Health & social care | 2025 |
| Okoh Studio Ltd | Professional & scientific | 2021 |
| Okpe Cipher Ltd | Professional & scientific | 2026 |
| Olamiposi Iyun Ltd | Financial services | 2025 |
| Old Farm Place Brick Court Ltd | Households | 2021 |
| Oliver France Sound Limited | Information & communication | 2009 |
| Oliver Green Ltd | Administrative & support | 2024 |
| Olivers 2017 Limited | Hospitality | 2018 |
| Olivia Black Studio Limited | Wholesale & retail | 2023 |
| Olivia Court Residents Limited | Real estate | 2012 |
| Olivia's Paint & Connect Community Interest Company | Education | 2025 |
| Olona Blossoms Limited | Administrative & support | 2022 |
| Olympos Yatching Ltd | Extraterritorial | 2024 |
| Olyra Capital Limited | Financial services | 2025 |
| OM Capital Advisory Ltd | Professional & scientific | 2020 |
| Omas Kitchen Ltd | Hospitality | 2026 |
| Omega Gynaecology Services Ltd | Health & social care | 2023 |
| Omega Ministries Ltd | Education | 2011 |
| Omegatron Electrical Limited | Construction | 2007 |
| Omnis Capital Holdings Ltd | Financial services | 2023 |
| OMO Fitters Ltd | Construction | 2017 |
| OMO Five Ltd | Wholesale & retail | 2024 |
| Ompire Ltd | Real estate | 2022 |
| Omved International UK Limited | Administrative & support | 2018 |
| ON Site Skills Ltd | Construction | 2018 |
| ON the Rise Coaching Limited | Professional & scientific | 2018 |
| On-Broadcast Communications Limited | Information & communication | 2010 |
| Onboard Software Ltd | Wholesale & retail | 2020 |
| One 0 SIX Communications Ltd | Professional & scientific | 2012 |
| One Art One World Ltd | Arts & recreation | 2019 |