| Nova Accessories Limited | Professional & scientific | 2005 |
| Nova Care & Support Services Ltd | Health & social care | 2025 |
| Nova Plant Limited | Professional & scientific | 2023 |
| Novachain Solutions Ltd | Professional & scientific | 2025 |
| Novatrain Ltd | Professional & scientific | 2025 |
| Novel Symbolic Ltd | Information & communication | 2025 |
| Novel Wines Ltd | Wholesale & retail | 2016 |
| Novelli Group Holdings Limited | Financial services | 2025 |
| Npors Limited | Administrative & support | 1997 |
| NRG Diesel Limited | Wholesale & retail | 2010 |
| NS Higgins Construction Limited | Construction | 2005 |
| Nuclear Quality Solutions Ltd | Professional & scientific | 2025 |
| Nudge Platform Limited | Information & communication | 2025 |
| NW Estates Ltd | Real estate | 2018 |
| NX Created Limited | Information & communication | 2025 |
| Nxstep Limited | Information & communication | 2008 |
| Nyscs Limited | Professional & scientific | 2025 |
| O J T Tree Services Ltd | Agriculture & fishing | 2019 |
| O&E Property Limited | Real estate | 2025 |
| O'Brien & Parry (Direct Carpets) Ltd | Wholesale & retail | 1998 |
| O'Rourke Groundworks Limited | Construction | 2017 |
| O.P.S Oldales Pipework Solutions Limited | Professional & scientific | 2015 |
| O42 Studio Limited | Professional & scientific | 2019 |
| Oakley & Company Limited | Professional & scientific | 2013 |
| Oakmere Barns Residents Association Limited | Administrative & support | 2004 |
| Oakmere Cars Limited | Wholesale & retail | 1982 |
| Oakmere Events Ltd | Arts & recreation | 2021 |
| Oakmere Stables Limited | Arts & recreation | 2015 |
| Oakmere Wealth Management Ltd | Professional & scientific | 2011 |
| Oakwalk Limited | Wholesale & retail | 1965 |
| OB1FINANCE Group Ltd | Professional & scientific | 2020 |
| Ocean Education & Consultancy Ltd | Education | 2025 |
| Oceans Entertainment Talent Agency Ltd | Administrative & support | 2024 |
| Ocelot Properties Limited | Real estate | 2022 |
| Odis Developments Ltd | Real estate | 2026 |
| Odiyana Kadampa Meditation Centre Ltd | Education | 1999 |
| Odst Ltd | Professional & scientific | 2017 |
| Odyssey Windows Ltd | Administrative & support | 2017 |
| OFF Grid Hideouts Limited | Hospitality | 2020 |
| Ogivy Sales Limited | Construction | 2025 |
| Ogma IT Services Limited | Information & communication | 2016 |
| OHN Limited | Professional & scientific | 2022 |
| Okells Groundworks & Landscaping Limited | Administrative & support | 2023 |
| Old Vicarage Lane Management Limited | Households | 1988 |
| Oldfield Engineering Limited | Professional & scientific | 2025 |
| Oldfield Painting Services Limited | Construction | 2025 |
| Olea & Opal Events Limited | Administrative & support | 2024 |
| Olitech Instrumentation Limited | Administrative & support | 2003 |
| Olive Beauty Limited | Other services | 2019 |
| Olive Mount Construction Developments Ltd | Construction | 2023 |
| Olive Tree Assets Limited | Real estate | 2016 |
| Oliver Gibney Hairdressing Ltd | Other services | 2024 |
| Oliver Technology Ltd | Information & communication | 2017 |
| Olivers Desserts Ltd | Hospitality | 2022 |
| Olivia Morgan Capital Ltd | Professional & scientific | 2024 |
| Olivv Ltd | Information & communication | 2026 |
| Omega Customs Solutions Limited | Transport & logistics | 2021 |
| Omnia-Klenz Ltd | Professional & scientific | 2011 |
| ON Record Media Limited | Extraterritorial | 2014 |
| ON Site Consultancy Ltd | Construction | 2015 |
| ON Site Services (Commercial Building Maintenance and Project Management) Limited | Administrative & support | 2006 |
| ON Site Services (Group) Limited | Professional & scientific | 2013 |
| One 2 One Support (Cheshire) Limited | Health & social care | 2008 |
| One Electrical Solutions Ltd | Construction | 2022 |
| One Nine Developments Limited | Construction | 2016 |
| One Nine Portfolio Ltd | Real estate | 2019 |
| Oneturn Services Ltd | Construction | 2025 |
| Onion Belt Interactive Ltd | Information & communication | 2025 |
| Online Services (Europe) Limited | Information & communication | 1989 |
| Online Worldwide Enterprise Ltd | Education | 2024 |
| Onro Properties Ltd | Real estate | 2023 |
| Onthepitch Group Ltd | Arts & recreation | 2026 |
| Open Road Engineering Limited | Professional & scientific | 2016 |
| Opulent Construction North West Ltd | Manufacturing | 2026 |
| Opus Creative Design Ltd | Administrative & support | 2007 |
| Oral Implants Limited | Health & social care | 2009 |
| ORBIT4 Group Limited | Financial services | 2019 |
| ORBIT4 UK Limited | Wholesale & retail | 2015 |
| Orchard Civil Engineering Company Ltd | Construction | 2024 |
| Orford Property Services Ltd | Real estate | 2017 |
| Organisational Learning Ltd | Education | 2025 |
| Origin Clothing (UK) Limited | Wholesale & retail | 2014 |
| OSI Survey Engineering Ltd | Construction | 2023 |
| OSS Commercial Flooring Limited | Construction | 2013 |
| OSS Electrical Services Limited | Construction | 2013 |
| OSS Managed Services Limited | Professional & scientific | 2013 |
| Osterna Limited | Administrative & support | 2002 |
| Otrera Aromatics Limited | Manufacturing | 2021 |
| Oultra Ltd | Construction | 2018 |
| Outsourced FD Services Ltd | Professional & scientific | 2018 |
| Outsourced Training Solutions Limited | Professional & scientific | 2012 |
| Overland Enterprises Ltd | Wholesale & retail | 1998 |
| Owen Law Limited | Professional & scientific | 2022 |
| Oxyl-Pro Limited | Extraterritorial | 2017 |
| Ozie the Goat Limited | Wholesale & retail | 2025 |
| Ozzie Logistics Ltd | Transport & logistics | 2025 |
| P & a Commercials (Wales) Ltd | Administrative & support | 2007 |
| P & C Energy Limited | Energy | 2022 |
| P a C C Limited | Information & communication | 2002 |
| P Dakin Construction Ltd | Construction | 2022 |