| NUTRI7 Limited | Hospitality | 2023 |
| Nuwave Properties Limited | Real estate | 2021 |
| NVA Artistic Ltd | Construction | 2026 |
| NVK Plastering Ltd | Construction | 2024 |
| NW Builders Ltd | Construction | 2022 |
| NW4 Property Limited | Real estate | 2021 |
| NWE Marlow 2 Ltd. | Construction | 2018 |
| Nwe.Uk. Ltd | Construction | 2006 |
| NWL DRY Cleaners Ltd | Other services | 2024 |
| NYK Consultants Ltd | Professional & scientific | 2007 |
| Nyleb SYS ENG Limited | Professional & scientific | 2014 |
| Nymo Global Limited | Information & communication | 2011 |
| Nynestar Entertainments Ltd | Information & communication | 2025 |
| NYS Construction Ltd | Construction | 2021 |
| O'Brien Security Protection Ltd | Administrative & support | 2017 |
| O2 Plumbing & Heating Services Ltd | Construction | 2019 |
| Oak Estates & Financial Services LLP | | 2023 |
| Oak Farm GAS Company Limited | Wholesale & retail | 2000 |
| Oak Grocery Ltd | Wholesale & retail | 2019 |
| Oak Leaf Education Ltd | Education | 2023 |
| Oak Mini Market Cake Shop Ltd | Wholesale & retail | 2023 |
| Oakdale UK Ltd | Health & social care | 2008 |
| Oakhart Associates Limited | Construction | 2000 |
| Oakliegh Estates Limited | Real estate | 2022 |
| Oakmead Residents Company Limited | Households | 1988 |
| Oakrise Limited | Real estate | 2000 |
| Oaks Furniture Ltd | Wholesale & retail | 2024 |
| Oaktree Global Ltd | Real estate | 2019 |
| Oaktree Properties (Harrow) Limited | Real estate | 2016 |
| Oakwood Property Ventures Ltd | Real estate | 2026 |
| Oakyrw Ltd | Real estate | 2019 |
| Oasis Space Therapy Ltd | Health & social care | 2024 |
| Obnh Limited | Other services | 2023 |
| Obolstar Limited | Households | 1993 |
| Obsidiane Solutions Limited | Professional & scientific | 2025 |
| OBY Construction Ltd | Construction | 2022 |
| Occasions 2000 Limited | Real estate | 1998 |
| Ocean Fisheries & Groceries Ltd | Wholesale & retail | 2015 |
| Oceans Limited | Transport & logistics | 1999 |
| Octagon Holding International Limited | Administrative & support | 2017 |
| Octopus Plumbing & Heating Ltd | Construction | 2025 |
| Octopus Squirt Prints Limited | Manufacturing | 2025 |
| Oculus Prime Ltd | Health & social care | 2025 |
| Odaan Limited | Wholesale & retail | 2018 |
| ODB Capital Limited | Real estate | 2024 |
| Oddjobz Ltd | Construction | 2019 |
| Odessa Construction Ltd | Construction | 2024 |
| ODM Project Consultants Ltd | Information & communication | 2022 |
| Odotechniki Ltd | Construction | 2015 |
| Offstats Consulting Limited | Professional & scientific | 2013 |
| Ofira Limited | Administrative & support | 2021 |
| Ofsc Limited | Wholesale & retail | 2024 |
| OGA V Entertainment Ltd | Information & communication | 2026 |
| OH Foods Ltd | Wholesale & retail | 2021 |
| Ohimaa Holland Textiles Ltd | Wholesale & retail | 2017 |
| OHR Yaakov Sephardi Congregation Limited | Health & social care | 2007 |
| Oiltech International (Services) Limited | Administrative & support | 1996 |
| OJ Stuff LLP | | 2021 |
| Ojay Wellness Services Ltd | Health & social care | 2025 |
| Okey 2 Invest Property Ltd | Real estate | 2025 |
| Okwi.Com Ltd | Information & communication | 2013 |
| Ola-Olu Investments Limited | Other services | 2019 |
| Olamide’S Empire Ltd | Health & social care | 2026 |
| Old Anandians Sports Club UK Limited | Arts & recreation | 2023 |
| Old London Road Management Company Limited | Households | 1993 |
| Oldmead Ltd | Real estate | 2024 |
| Oleksandr Chabanenko Ltd | Transport & logistics | 2021 |
| Oleksandr Chornenkyi Limited | Construction | 2025 |
| Olive Court Property Management Limited | Real estate | 2011 |
| Olive Grove Retail Ltd | Wholesale & retail | 2024 |
| Olive Tree Carers Ltd | Administrative & support | 2024 |
| Olliechick Limited | Arts & recreation | 2021 |
| Olney TCF Holdings Limited | Real estate | 2024 |
| Olsi Building Services Ltd | Construction | 2023 |
| Olysquared Ltd | Other services | 2020 |
| OM Associates Limited | Professional & scientific | 2005 |
| OM Building Solution Ltd | Construction | 2022 |
| OM Creatives Limited | Other services | 2011 |
| OM Diagnostics Limited | Health & social care | 2019 |
| OM Legal Limited | Professional & scientific | 2022 |
| OM Sridaya Namaha Limited | Real estate | 2024 |
| Om-Sol Limited | Wholesale & retail | 2020 |
| OMA Capital Limited | Real estate | 2026 |
| OMB. Care Ltd | Health & social care | 2025 |
| OMC (London) Trading and Investments Ltd | Administrative & support | 2021 |
| OMC Opportunity Ltd | Construction | 2013 |
| Omera Group Ltd | Wholesale & retail | 2025 |
| OMG Smiles Limited | Financial services | 2023 |
| OMH Consulting Ltd | Administrative & support | 2014 |
| Omnicare Accommodation Limited | Real estate | 2018 |
| Omniclub Ltd | Information & communication | 2024 |
| Omniliving Ltd | Real estate | 2017 |
| Omniprop Capital 2 Limited | Real estate | 2026 |
| Omniprop Capital Ltd | Real estate | 2017 |
| Omnistudent Living Limited | Hospitality | 2024 |
| Omniveritas Limited | Information & communication | 2024 |
| ON Track Montessori Limited | Education | 2017 |
| Onandonlondon Limited | Manufacturing | 2025 |
| Oncology Imaging Limited | Health & social care | 2017 |
| One Ashcombe Gardens Limited | Construction | 2017 |