| Nuvision Essex Limited | Professional & scientific | 2023 |
| Nuvision London Limited | Professional & scientific | 2023 |
| NV IT Solutions Limited | Information & communication | 2023 |
| NV Lettings Ltd | Real estate | 2023 |
| NVG Developments Ltd | Real estate | 2025 |
| Nvpc Limited | Information & communication | 2011 |
| Nvsc Holdings Ltd | Real estate | 2025 |
| Nvsc SPV 1 Ltd | Real estate | 2026 |
| NXT Properties Ltd | Real estate | 2022 |
| Nxtgen Products Ltd | Wholesale & retail | 2024 |
| O Space Design and Consulting Limited | Professional & scientific | 2014 |
| O Stokes Holdings Limited | Financial services | 2026 |
| O&S Consultancy Services Ltd | Professional & scientific | 2026 |
| O'N'O Facilities Services Ltd | Administrative & support | 2021 |
| O'Riordan Construction Limited | Construction | 2009 |
| O'Riordan Properties Limited | Households | 2013 |
| Oakflooring Ltd | Construction | 2020 |
| Oakland Build-Plant Limited | Construction | 2022 |
| Oakland Management Limited | Real estate | 2015 |
| Oakleigh FM Limited | Administrative & support | 2026 |
| Oakmont Property Consultants Ltd | Real estate | 2021 |
| Oana Services Limited | Construction | 2025 |
| Oandmorie Limited | Wholesale & retail | 2024 |
| Oasis Banqueting Ltd. | Hospitality | 2015 |
| Oates Electrical & Building Services Limited | Construction | 2018 |
| OBD1357 Mechanic Ltd | Wholesale & retail | 2025 |
| OBE Dining Ltd | Hospitality | 2026 |
| Obelisk Computers Limited | Information & communication | 1988 |
| OBI Solutions Ltd | Information & communication | 2010 |
| Obris Ltd | Professional & scientific | 2022 |
| OBS Designs Limited | Professional & scientific | 2013 |
| Ocean House Cleaning Group Ltd | Administrative & support | 2025 |
| Oceanwide Freight Services Limited | Transport & logistics | 2015 |
| Oden Properties Limited | Real estate | 2024 |
| Office Print and Framing Limited | Wholesale & retail | 2019 |
| Official Bitcoin Channel Ltd | Information & communication | 2020 |
| Official Bitcoin Company Ltd | Information & communication | 2019 |
| Offset My Impact Limited | Professional & scientific | 2021 |
| Oikia Law Properties Ltd | Real estate | 2026 |
| Oink BBQ Limited | Hospitality | 2019 |
| Ojas Events Ltd | Hospitality | 2025 |
| Okar Consulting Ltd | Financial services | 2016 |
| Olamide Courier Ltd | Transport & logistics | 2026 |
| Old East Ltd | Construction | 2016 |
| OLE Foods Limited | Extraterritorial | 2011 |
| Olea of Leigh Ltd | Hospitality | 2018 |
| Olive Academies | Education | 2013 |
| Olive Academies Independent Schools | Education | 2025 |
| Olive Bricks Ltd | Real estate | 2023 |
| Olive Cybernetics Ltd | Information & communication | 2025 |
| Olive Probate Limited | Public administration | 2025 |
| Olive Tax and Estate Planning Ltd | Professional & scientific | 2025 |
| Olympus Construction Ltd | Construction | 2020 |
| Omar Medical Limited | Health & social care | 2011 |
| Omas Care Limited | Health & social care | 2021 |
| OMB Services Ltd | Hospitality | 2023 |
| OME Cleaning Ltd | Administrative & support | 2026 |
| Omega Facades U.K Limited | Construction | 2024 |
| Omega Investments & Holdings Ltd | Real estate | 2017 |
| Omnident UK Ltd | Wholesale & retail | 2015 |
| Omokaro UK Limited | Other services | 2013 |
| ON a Positive Note Ltd | Manufacturing | 2017 |
| Oncera Limited | Information & communication | 2025 |
| Oncu Food Centre Trading Ltd | Wholesale & retail | 2021 |
| One Hygienist Ltd | Health & social care | 2019 |
| One Innovate Ltd | Information & communication | 2023 |
| One Misket Ltd | Other services | 2018 |
| Onestop Brokers Limited | Administrative & support | 2003 |
| Ongar Road Dental Surgery Limited | Health & social care | 2007 |
| Only Way IS Weddings Limited | Other services | 2018 |
| Onniejean Property Ltd | Real estate | 2019 |
| Onpoint Global Limited | Construction | 2019 |
| Onslaught Music Limited | Information & communication | 2008 |
| Onwards and Upwards Ltd | Information & communication | 2017 |
| Onyx Body and Skin Ltd | Hospitality | 2026 |
| Onyx Squares Ltd | Wholesale & retail | 2026 |
| Ophthalmotech Limited | Health & social care | 2009 |
| Opifex Microcement Ltd | Construction | 2024 |
| Optical Money Ltd | Extraterritorial | 2008 |
| Optima Talent Ltd | Administrative & support | 2026 |
| Optimal Caretech Solutions Ltd | Administrative & support | 2021 |
| Optimised Assets Ltd | Real estate | 2026 |
| Optimum Thermal Solutions Ltd | Construction | 2025 |
| Optom Solutions Limited | Administrative & support | 2003 |
| Opus Window Company Limited | Construction | 1995 |
| Oral Maxillo Facial Surgery Limited | Health & social care | 2012 |
| Orange 14 Limited | Real estate | 2024 |
| Orange Fields Ltd | Construction | 2022 |
| Orange Juice Entertainment Ltd | Arts & recreation | 2023 |
| Orbital Homes Limited | Real estate | 2022 |
| Orchard Court (Hornchurch) Limited | Households | 1968 |
| Orchid Montessori Nursery School Limited | Education | 2007 |
| Oreoluwa Limited | Administrative & support | 2023 |
| Orford Hill Limited | Health & social care | 2006 |
| Organichimalayanfood Ltd | Wholesale & retail | 2025 |
| Original Bitcoin Company Ltd | Information & communication | 2019 |
| Original Bitcoin Exchange Ltd | Extraterritorial | 2019 |
| Original Kebabish Ltd | Hospitality | 2026 |
| Original Thai Massage Ltd | Other services | 2024 |
| Orlake Records Limited | Wholesale & retail | 2025 |