| Nottingham Road Limited | Real estate | 2023 |
| Nova Moon Ltd | Arts & recreation | 2024 |
| Nova Sales and Distribution (UK) Limited | Information & communication | 2001 |
| Novacomms Network Ltd | Information & communication | 2023 |
| Novalq Ltd | Information & communication | 2024 |
| Novalun Ltd | Health & social care | 2025 |
| Novita Global Ltd | Wholesale & retail | 2025 |
| Noya Solutions Ltd | Information & communication | 2018 |
| NP Completions Limited | Professional & scientific | 2023 |
| NP Employment Solutions Ltd | Administrative & support | 2019 |
| Nph&B Ltd | Real estate | 2012 |
| NRG Construction (UK) Ltd | Construction | 2010 |
| NRG Consultancy Services Limited | Professional & scientific | 2017 |
| NRK DM Consultancy Limited | Professional & scientific | 2023 |
| NS Digital Creative Ltd | Other services | 2012 |
| Nsml Business Group Ltd | Information & communication | 2026 |
| Nsure Consulting Ltd | Professional & scientific | 2025 |
| NT Hotels Ltd | Hospitality | 2022 |
| Ntrapt Ltd | Wholesale & retail | 2025 |
| Nucit Ltd | Information & communication | 2021 |
| Nuff Respect Limited | Professional & scientific | 1992 |
| Nugasie Ltd | Construction | 2021 |
| Number 9 Property Limited | Real estate | 2005 |
| Number Eight ST Andrews Square Limited | Other services | 2007 |
| Nursery CPD Ltd | Information & communication | 2024 |
| NV Pro Ltd | Real estate | 2018 |
| Nxtgenevowear Limited | Wholesale & retail | 2025 |
| O&O Ltd | Real estate | 2025 |
| O1 Inventories Limited | Real estate | 2014 |
| OAG Consulting Limited | Information & communication | 2016 |
| Oak and River Holdings Limited | Financial services | 2026 |
| Oak Forest International Ltd | Other services | 2024 |
| Oak Hill Fencing Limited | Construction | 2017 |
| Oakdene (ST. Mary's Road) Residents Association Limited | Households | 1991 |
| Oakdene Freehold Management Limited | Households | 2016 |
| Oakdene Holdings Limited | Professional & scientific | 2007 |
| Oakdene Hotels Limited | Hospitality | 1997 |
| Oakenshaw Court Residents Association Limited | Households | 1960 |
| Oakhill Court (Management) Limited | Households | 1977 |
| Oakhill Court (Residents) Limited | Real estate | 2020 |
| Oakleigh Court Limited | Households | 1979 |
| Oakmount Estates Limited | Professional & scientific | 1990 |
| Oaks Park Cafe Limited | Hospitality | 2014 |
| Oakton Consult Limited | Professional & scientific | 2025 |
| Obelisk Risk and Financial Services Limited | Administrative & support | 2023 |
| Obon Foods Ltd | Hospitality | 2018 |
| Obsidian Contracting Ltd | Construction | 2023 |
| Obsidian Flame Studios Ltd | Wholesale & retail | 2023 |
| Obythree Limited | Information & communication | 2017 |
| Ockram Asset Co Ltd | Real estate | 2015 |
| Odin Data Limited | Administrative & support | 2019 |
| Odyssey Accounting Services Limited | Professional & scientific | 2019 |
| Odyssey Sport Limited | Professional & scientific | 2025 |
| Offbeat Booking Limited | Hospitality | 2025 |
| Ogis Builders Ltd | Construction | 2020 |
| OH Property Development Ltd | Construction | 2022 |
| Ohaana Chinese Limited | Hospitality | 2025 |
| Old Street Strategy Limited | Administrative & support | 2017 |
| Oldfield Court (Surbiton) Residents Association Limited | Households | 1964 |
| Olive Pizza Limited | Hospitality | 2026 |
| Oliver Properties Limited | Households | 1987 |
| Olivia Shaw Acupuncture Ltd | Health & social care | 2014 |
| Olivier's Bakery Ltd | Hospitality | 2011 |
| OLR Events CIC | Arts & recreation | 2023 |
| Olteanu Construct Ltd | Construction | 2026 |
| Omarketing Limited | Professional & scientific | 1999 |
| Ominterpreting Ltd | Professional & scientific | 2022 |
| Omletto Ltd | Households | 2018 |
| Ommadawn Ltd | Construction | 2015 |
| Omnira Holdings Limited | Financial services | 2025 |
| ON Smoke BBQ and Pizza Ltd | Hospitality | 2025 |
| One Red Wall Limited | Professional & scientific | 2011 |
| One Saint Leonards Road Limited | Households | 2004 |
| Onestopmedicine Ltd | Education | 2025 |
| Oneten Products Ltd | Wholesale & retail | 2024 |
| Onethousandvolts Ltd | Education | 2021 |
| Oneul Ltd | Wholesale & retail | 2025 |
| Online Minicabs Ltd | Transport & logistics | 2022 |
| Online Retail Ltd | Wholesale & retail | 2014 |
| Only Coders Ltd | Information & communication | 2023 |
| Only Walls and Ceilings Ltd | Construction | 2025 |
| Onyx Studios Limited | Information & communication | 2018 |
| Open Sesame Media Limited | Information & communication | 2024 |
| Opening Gates Ltd | Real estate | 2020 |
| Opening Gates Property Management LLP | | 2022 |
| Operify Ltd | Information & communication | 2026 |
| Ophthalmic Surgical Services Ltd | Health & social care | 2015 |
| Opportunity Central (UK) Ltd | Other services | 2014 |
| Opticall Limited | Health & social care | 2009 |
| Optics Eyecare Limited | Wholesale & retail | 2022 |
| Optiliti Limited | Information & communication | 2016 |
| Optimum Econsultancy Ltd | Information & communication | 2023 |
| Opulence Care Ltd | Health & social care | 2015 |
| OPY Holdings Ltd | Administrative & support | 2009 |
| ORBIT8 Ltd | Information & communication | 2026 |
| Orca Ecommerce Limited | Wholesale & retail | 2026 |
| Ordo Technologies Ltd | Information & communication | 2026 |
| Ordonia Care Services Limited | Health & social care | 2018 |
| Orenda 2008 Ltd | Construction | 2016 |
| Oreo Property Solutions Limited | Real estate | 2023 |