| NRA Dermatology Ltd | Health & social care | 2024 |
| NRD Solutions Ltd | Wholesale & retail | 2025 |
| NS Enterprises North Ltd | Other services | 2017 |
| NS Media News Limited | Wholesale & retail | 2008 |
| NS Tooling Services Limited | Manufacturing | 2003 |
| NSD Dental Limited | Health & social care | 2022 |
| NT Allard Ltd | Construction | 2016 |
| Ntbs Investments Ltd | Real estate | 2016 |
| Ntic UK Limited | Professional & scientific | 2024 |
| Nuddock Lodges Limited | Hospitality | 2023 |
| Nuddock Wood Lake & Lodges Limited | Real estate | 2023 |
| NUR Muzaiek UK Ltd | Wholesale & retail | 2024 |
| Nutr. Ltd | Hospitality | 2021 |
| Nutrocore Ltd | Manufacturing | 2025 |
| Nyeve Ltd | Transport & logistics | 2025 |
| O DE Brett Anaesthesia Ltd | Health & social care | 2022 |
| O&N Transport Ltd | Transport & logistics | 2015 |
| O'Hara Financial Limited | Financial services | 2005 |
| OA Ltd | Health & social care | 2023 |
| Oades Close Management Limited | Extraterritorial | 2020 |
| Oak Road Properties Limited | Construction | 2021 |
| Oakbridge Joinery Ltd | Construction | 2025 |
| Oakheart Services Ltd | Hospitality | 2015 |
| Oakhill Prime Estates Limited | Real estate | 2025 |
| Oakstead Homes Developments UK Limited | Construction | 2025 |
| Oakwood Tree Limited | Agriculture & fishing | 2003 |
| Oatridge Coaching Ltd | Health & social care | 2021 |
| Oboz Logistics Limited | Transport & logistics | 2025 |
| Ocean Family Rolex Ltd | Hospitality | 2026 |
| Oceanjoule Limited | Manufacturing | 2010 |
| OCG Legal Ltd | Professional & scientific | 2010 |
| Ocs-Uk Limited | Professional & scientific | 2022 |
| October House Environmental Limited | Water & waste | 2003 |
| Odds Notify Ltd | Information & communication | 2022 |
| Odyssey Holdings Limited | Professional & scientific | 2000 |
| Office Maid Ltd | Administrative & support | 2017 |
| Ogdan Construct Ltd | Construction | 2024 |
| Ogg's Haulage (Scunthorpe) Ltd | Transport & logistics | 2015 |
| OH WOW Desserts Limited | Hospitality | 2025 |
| Ohana Childcare Services Ltd | Education | 2026 |
| OIL Equipment Limited | Manufacturing | 2010 |
| Olan's Tonsorial Ltd | Other services | 2025 |
| Olive Garden Restaurant Limited | Hospitality | 2013 |
| Oliver Colfort Limited | Construction | 2013 |
| OLOTRUCKNO3 Ltd | Transport & logistics | 2023 |
| Olsza.Transport Ltd | Transport & logistics | 2018 |
| Omahts Ltd | Wholesale & retail | 2015 |
| Omar & Brothers Ltd | Wholesale & retail | 2021 |
| Omar Painting & Decorating Ltd | Construction | 2026 |
| Omega Data Tech Ltd | Construction | 2024 |
| Omega Hydrogen Ltd | Manufacturing | 2024 |
| Omkar Ventures Ltd | Real estate | 2022 |
| Omnis & Co Maintenance Ltd | Administrative & support | 2025 |
| Omnis Aggregates Limited | Transport & logistics | 2013 |
| Omnis Group Holdings Ltd | Financial services | 2021 |
| Omonemi Limited | Health & social care | 2018 |
| ON the Move Property Investments Ltd | Real estate | 2026 |
| Oncogenix Care Limited | Health & social care | 2025 |
| One Food Safety Services Ltd | Professional & scientific | 2025 |
| One for the Girls Community Interest Company | Health & social care | 2024 |
| One for the Lads Community Interest Company | Health & social care | 2019 |
| One Time Only by Kerry Ltd | Arts & recreation | 2019 |
| Ongo Communities Limited | Other services | 2013 |
| Ongo Developments Limited | Construction | 2017 |
| Ongo Heating & Plumbing Limited | Construction | 2016 |
| Ongo Recruitment Limited | Administrative & support | 2003 |
| Ongo Roofing Limited | Construction | 2014 |
| Only Daughter TV Limited | Information & communication | 2025 |
| Onoka LLP | | 2024 |
| Onssa Camper Van Ltd | Manufacturing | 2024 |
| Onyi Limited | Health & social care | 2014 |
| Onyx European Limited | Transport & logistics | 2025 |
| Onyx Freight Services Limited | Transport & logistics | 2022 |
| Opal and Garnet Aesthetics Ltd | Health & social care | 2021 |
| Opal Organics UK Limited | Wholesale & retail | 2025 |
| Opal Specialist Finance Ltd | Financial services | 2017 |
| Operator Training Solutions Limited | Education | 2009 |
| Opticfx Ltd | Information & communication | 2025 |
| Orange 1 Shop Ltd | Wholesale & retail | 2025 |
| Original Detailing Ltd | Wholesale & retail | 2024 |
| Osbourne Estates Limited | Real estate | 2009 |
| Oscar Products Limited | Wholesale & retail | 2007 |
| OSH Gosh Gowns Ltd | Wholesale & retail | 2011 |
| OSI Food Solutions UK Holdings Limited | Professional & scientific | 1990 |
| OSI Food Solutions UK Limited | Manufacturing | 1978 |
| OSI Investment UK Limited | Professional & scientific | 2010 |
| Osman Money Transfer Ltd | Financial services | 2021 |
| Osprey Furniture Ltd | Manufacturing | 2020 |
| Ostara Living Limited | Wholesale & retail | 2020 |
| Osvision Ltd | Health & social care | 2018 |
| Oswin Electrical Ltd | Construction | 2022 |
| OT Auto Valeting Ltd | Wholesale & retail | 2021 |
| Othi Consulting Ltd | Professional & scientific | 2020 |
| Outdoor and Indoor Ltd | Wholesale & retail | 2024 |
| Outlaw Boxing UK Ltd | Wholesale & retail | 2025 |
| Over the Board Limited | Professional & scientific | 2023 |
| Over the Top Events Ltd | Hospitality | 2018 |
| Overhall Aggregates Limited | Mining & quarrying | 2018 |
| Overhall Developments Limited | Real estate | 2019 |
| Overhall Farms Limited | Agriculture & fishing | 2024 |