| Nothing BUT Value Ltd | Information & communication | 2026 |
| Nova Huntingdon Ltd | Wholesale & retail | 2025 |
| Nova Performance Group Ltd | Wholesale & retail | 2026 |
| Nova Retail Solutions Ltd | Wholesale & retail | 2026 |
| Nova Soundworks Ltd | Administrative & support | 2024 |
| Novare Developments Ltd | Real estate | 2018 |
| Novario Ventures Ltd | Professional & scientific | 2026 |
| Novo Motors Limited | Wholesale & retail | 2017 |
| Novo Product Design Limited | Manufacturing | 2010 |
| NOW Appliance Rental Ltd | Administrative & support | 2024 |
| NPI Property Limited | Real estate | 2022 |
| NRC Catering Ltd | Hospitality | 2019 |
| NRC Staffing Ltd | Administrative & support | 2025 |
| NRH Electrical Services Ltd | Administrative & support | 2011 |
| Nrhr Ltd. | Administrative & support | 2016 |
| NS Auto Repair Ltd | Wholesale & retail | 2020 |
| Nufuture Fitness Ltd | Arts & recreation | 2024 |
| Numbers 2 Knowledge (N2K) Ltd | Professional & scientific | 2023 |
| Nuoto Ltd | Arts & recreation | 2021 |
| Nurture Space Ltd | Education | 2024 |
| NUTZ4NUTS Limited | Wholesale & retail | 2016 |
| Nuush Ltd | Health & social care | 2012 |
| O'Dell Heating & Plumbing Limited | Construction | 2012 |
| O'Neil Developments Limited | Construction | 2025 |
| Oak Acres Road Management Company Limited | Households | 2019 |
| Oak Tree Anglia Limited | Wholesale & retail | 2020 |
| Oakfield Business Corner Ltd | Administrative & support | 2005 |
| Oakleaf Property Developments Ltd. | Information & communication | 2001 |
| Oakleaf Solutions Limited | Information & communication | 2003 |
| Oaktree Projects Fenland Limited | Construction | 2005 |
| Oakwater Projects Ltd | Real estate | 2015 |
| Obero Tech Limited | Information & communication | 2025 |
| OBP Motorsport Limited | Manufacturing | 2019 |
| OBP Special Operations Limited | Extraterritorial | 2020 |
| Obsessionism Photography Ltd | Extraterritorial | 2024 |
| OC Klean Ltd | Transport & logistics | 2026 |
| Ocean Tails Ltd | Other services | 2025 |
| Ochoa Global Creative Ltd | Hospitality | 2015 |
| ODD Jobs Ltd | Administrative & support | 2015 |
| Odelia Consulting Ltd | Information & communication | 2023 |
| ODH Consultants Ltd | Professional & scientific | 2025 |
| Odin Lifestyle Limited | Wholesale & retail | 2017 |
| Odyssey Fire & Life Safety Solutions Ltd | Construction | 2026 |
| Offord Hill Consulting Limited | Administrative & support | 2008 |
| Offord Hill Maintenance Ltd | Construction | 2023 |
| OHL Land Holdings Limited | Real estate | 2019 |
| OHL Piper Limited | Real estate | 2021 |
| OHL Property Holdings Limited | Professional & scientific | 2019 |
| Ohmsafe Fire and Security Limited | Administrative & support | 2019 |
| Ohoka Properties Limited | Real estate | 2025 |
| Oikoi Ltd | Real estate | 2018 |
| Okalya Ltd | Wholesale & retail | 2025 |
| Old Cottage Close Management Company Limited | Households | 2000 |
| Oliveoliveuk Ltd. | Hospitality | 2013 |
| Oliver Charles Group Ltd | Transport & logistics | 2025 |
| Oliver James Property Investments Limited | Real estate | 2023 |
| Oliver James Property Sales and Lettings Ltd | Real estate | 2019 |
| Olivers Limited | Wholesale & retail | 1997 |
| Ollego Ltd | Professional & scientific | 2013 |
| Ollie Martin Ltd | Wholesale & retail | 2026 |
| Olober Ltd | Wholesale & retail | 2023 |
| OLT 75 Limited | Transport & logistics | 2021 |
| OM UK Properties Ltd | Real estate | 2022 |
| Omega Transport DM Ltd | Transport & logistics | 2014 |
| Omex (UK) Limited | Professional & scientific | 1996 |
| Omex Agricultural Holdings Ltd. | Manufacturing | 1973 |
| Omex International Ltd | Extraterritorial | 2023 |
| Omni Dental Sciences Limited | Health & social care | 1998 |
| Omni Security Services Limited | Administrative & support | 2001 |
| Omnidogs Limited | Agriculture & fishing | 2021 |
| Omoro Events Ltd | Arts & recreation | 2021 |
| Online Sale Stars Limited | Wholesale & retail | 2023 |
| Onyx Sports Group Ltd | Wholesale & retail | 2023 |
| OOC Solutions Ltd | Information & communication | 2017 |
| Opal Lettings Limited | Hospitality | 2016 |
| Opalbond Limited | Wholesale & retail | 1999 |
| Opalbond Nutrition Limited | Manufacturing | 2015 |
| Open Heritage AI Limited | Arts & recreation | 2025 |
| Opscore Services Ltd | Professional & scientific | 2025 |
| Opsydium Limited | Professional & scientific | 2014 |
| Optilight Limited | Manufacturing | 2004 |
| Optima Source Limited | Wholesale & retail | 2026 |
| Optimum Balance Products Limited | Manufacturing | 2007 |
| Optimum Property Consultancy Limited | Professional & scientific | 2013 |
| Optimum Trade Supplies Limited | Wholesale & retail | 2010 |
| Optometric Solutions Limited | Health & social care | 2015 |
| Oraldent Limited | Health & social care | 1985 |
| Orange Imports Limited | Wholesale & retail | 2004 |
| Orange Rose Accounting Limited | Professional & scientific | 2026 |
| Organic Boutique Ltd | Wholesale & retail | 2024 |
| Organic by Design (Construction) Ltd | Construction | 2022 |
| Organic by Design Ltd | Construction | 2020 |
| Organic Roasted Coffee Ltd | Manufacturing | 2018 |
| Orientrose Contracts Limited | Construction | 2002 |
| Orientrose Trustee Limited | Extraterritorial | 2020 |
| Origin UW Limited | Financial services | 2013 |
| Orma Home Ltd | Manufacturing | 2022 |
| Ortholove Limited | Manufacturing | 2017 |
| Oscars Wine Bar Ltd | Hospitality | 2026 |
| OSKI81 Ltd | Transport & logistics | 2019 |