| Nuttall Ltd | Hospitality | 2018 |
| Nuttall Property Ltd | Real estate | 2024 |
| Nuvio Software Solutions Limited | Information & communication | 2016 |
| Nuwf 186 Limited | Hospitality | 2024 |
| Nuwf Limited | Hospitality | 2024 |
| NV Estates 2023 Ltd | Real estate | 2023 |
| Nvacn Co. Ltd | Health & social care | 2025 |
| Nvrj Masons Limited | Hospitality | 2021 |
| NW HI Ltd | Construction | 2019 |
| NW Newport Limited | Hospitality | 2026 |
| NYE Media Ltd | Information & communication | 2022 |
| Nylah’S Nest Ltd | Manufacturing | 2025 |
| Nyoka Services Limited | Health & social care | 2021 |
| NZN Transport Ltd | Transport & logistics | 2025 |
| NÛR Dental Laboratory Ltd | Manufacturing | 2022 |
| O Apparel NG Limited | Water & waste | 2025 |
| O Blake Properties Ltd | Real estate | 2023 |
| O&S Composite/Laminate Company Ltd | Manufacturing | 2024 |
| O'Connell Cars & Commercials Ltd | Wholesale & retail | 2012 |
| O'Connor's (UK) Limited | Manufacturing | 2015 |
| O'Mullane Consultancy Limited | Professional & scientific | 2014 |
| O-Yes Pizza Kebab House Ltd | Hospitality | 2019 |
| O.C Rail Ltd | Construction | 2020 |
| O.H Property Services Limited | Construction | 2021 |
| OA Living Ltd | Real estate | 2023 |
| Oak and Rose Enterprises Ltd | Wholesale & retail | 2024 |
| Oak Clinical Services Limited | Health & social care | 2014 |
| Oak Grange Isle of Wight (Management) Limited | Households | 2006 |
| Oak Tree Green Ltd | Wholesale & retail | 2023 |
| Oak Tree Residencies Ltd | Real estate | 2022 |
| Oakdale Commercial Limited | Construction | 2000 |
| Oakdale Heating and Plumbing Limited | Construction | 2025 |
| Oakdale Technical Services Ltd | Construction | 2004 |
| Oakfield 47 Ltd | Construction | 2026 |
| Oakfield Crescent Ltd | Financial services | 2022 |
| Oakhill Landscapes and Construction Ltd | Administrative & support | 2025 |
| Oakhill Landscapes Limited | Other services | 2003 |
| Oaklands Bungalows Management Limited | Households | 2023 |
| Oaklands Management Company (Christchurch) Limited | Households | 1985 |
| Oaklands Management Company (IOW) Limited | Households | 2014 |
| Oakleaf Building Contractors Ltd | Construction | 2021 |
| Oaklee Associates Ltd | Construction | 2026 |
| Oaklee Construction Limited | Construction | 2021 |
| Oakley Customs Ltd | Wholesale & retail | 2023 |
| Oakley Properties (South Wales) Ltd | Real estate | 2017 |
| Oakleys Barbers Ltd | Other services | 2020 |
| Oakleys Luxury Jewellery & Watches Ltd | Wholesale & retail | 2025 |
| Oaks Country Kennels Limited | Agriculture & fishing | 2018 |
| Oakwood Property Holdings Limited | Real estate | 2018 |
| Oakwood Student Accommodation Limited | Construction | 2013 |
| Oarsome Potential Limited | Manufacturing | 2007 |
| Oasis Estates Limited | Real estate | 2025 |
| Oasis Express Limited | Wholesale & retail | 2025 |
| Oasis Laundrette Company Ltd | Other services | 2024 |
| Oasis Metal Products Limited | Manufacturing | 1990 |
| Oasis Support Ltd | Health & social care | 2022 |
| OB Kicks Ltd | Administrative & support | 2018 |
| Obeidatmedical Ltd | Wholesale & retail | 2025 |
| Objective Markers Ltd | Professional & scientific | 2025 |
| Obree Coaching Limited | Health & social care | 2022 |
| Obriens Hospitality Ltd | Arts & recreation | 2018 |
| Obsurv Ltd | Real estate | 2018 |
| Ocas Cleaning Services Ltd | Administrative & support | 2025 |
| Occupational Health and Safety Bureau Limited | Other services | 2009 |
| OCD Ltd | Information & communication | 2015 |
| OCD Technology Limited | Professional & scientific | 2011 |
| Ocdcds Domestic Cleaning Ltd | Administrative & support | 2020 |
| Ocdcds Holdings Ltd | Real estate | 2026 |
| Ocdcds Limited | Administrative & support | 2019 |
| Ocean Park Sports Education CIC | Arts & recreation | 2019 |
| Oceanic Traders Ltd | Transport & logistics | 2017 |
| Oceanscleaning Limited | Administrative & support | 2025 |
| Oceansun Flux Ltd | Information & communication | 2025 |
| Ochiltree House Management Limited | Households | 1993 |
| Octagon (Isle of Wight) Limited | Households | 2003 |
| Octanehairstudio Limited | Other services | 2022 |
| Octopod UK Ltd | Information & communication | 2025 |
| Octopus Communications Ltd | Professional & scientific | 2024 |
| OD IT Consultancy Ltd | Information & communication | 2011 |
| ODD Pals Ltd | Hospitality | 2025 |
| ODD Spot Events Ltd. | Health & social care | 2025 |
| Oddjobrobb Ltd | Wholesale & retail | 2025 |
| Oddy Partnership LLP | | 2025 |
| ODG Coaching Services Limited | Arts & recreation | 2025 |
| ODS Group Ltd | Other services | 2021 |
| OEM Bitz Ltd | Wholesale & retail | 2017 |
| Office Visions (Wales) Limited | Professional & scientific | 1975 |
| Offline Advertising Limited | Professional & scientific | 2022 |
| OG Innovation Ltd | Real estate | 2023 |
| OG International Holdings Limited | Professional & scientific | 2019 |
| OG Personal Training Ltd | Other services | 2026 |
| OG23 Properties Ltd | Real estate | 2019 |
| OG2303 Ltd | Arts & recreation | 2018 |
| Ogarnij Finanse Ltd | Education | 2025 |
| OH SO & Co Retail Ltd | Wholesale & retail | 2007 |
| OH SO Cherished Ltd | Wholesale & retail | 2019 |
| Oh's Transport Ltd | Transport & logistics | 2019 |
| OJ Health Ltd | Health & social care | 2024 |
| Ojmax Ltd | Administrative & support | 2021 |
| OK Taxi Ltd | Transport & logistics | 2022 |