| Origin Engineering Ltd | Manufacturing | 2016 |
| Original Fine Art 13 LLP | | 2024 |
| Orinoco Developments Limited | Construction | 2025 |
| Orion Court RTM Company Limited | Households | 2015 |
| Orion's Globe Limited | Administrative & support | 2020 |
| Orvynt Ltd | Information & communication | 2016 |
| Osborne Food Limited | Hospitality | 2019 |
| Osborne Marketing Ltd | Information & communication | 2000 |
| Osborne Place Ferndown Limited | Extraterritorial | 2011 |
| OSC Construction Ltd | Construction | 2010 |
| Oscap Group Ltd | Financial services | 2025 |
| Oscap Ltd | Professional & scientific | 2020 |
| Oscarmerr Ltd | Information & communication | 2025 |
| OSM Digital Ltd | Information & communication | 2016 |
| Osmani's Fried Chicken Limited | Hospitality | 2026 |
| Osmania Apparel Ltd | Wholesale & retail | 2026 |
| OSO Simple Ltd | Information & communication | 2022 |
| OSR Agile Consulting Ltd | Information & communication | 2019 |
| Ossua ET Acroamata Limited | Wholesale & retail | 2019 |
| Ostlers Yard Holdings Ltd | Hospitality | 2020 |
| Ostlers Yard Properties Ltd | Real estate | 2024 |
| OTG Ltd | Information & communication | 2018 |
| Other Choice Ltd | Transport & logistics | 2023 |
| Otis Clay Photographic Ltd | Professional & scientific | 2021 |
| Otlantic Ltd | Construction | 2014 |
| Otor Media Ltd | Manufacturing | 2024 |
| Otter Bookbinding Limited | Professional & scientific | 2013 |
| Otter Security Solutions Ltd | Administrative & support | 2026 |
| Ottershoot Limited | Financial services | 2021 |
| Otto Coffee Limited | Hospitality | 2019 |
| Otto Global Limited | Other services | 2018 |
| Otto House Ltd | Financial services | 2022 |
| Otto Print & Design Ltd | Professional & scientific | 2011 |
| Ottowalluk Ltd | Wholesale & retail | 2023 |
| Ouija Escape Experiences Ltd | Arts & recreation | 2022 |
| Ounce Coffee Collective Ltd | Hospitality | 2020 |
| OUR Little Shop Limited | Wholesale & retail | 2026 |
| OUR Place Bournemouth Ltd | Wholesale & retail | 2022 |
| OUT & About Dog Walking Ltd | Other services | 2026 |
| OUT of Hand Solutions Limited | Information & communication | 2026 |
| Outdoor Designs (Landscapes) Limited | Administrative & support | 2025 |
| Outdoor Designs (Maintenance) Limited | Administrative & support | 2009 |
| Outlaw Industries Ltd | Manufacturing | 2020 |
| Outline Acquisitions Limited | Professional & scientific | 2001 |
| Outpost VFX Limited | Information & communication | 2012 |
| Outside-Spaceuk Ltd | Administrative & support | 2021 |
| Overbury's Fine Arts Supplies Ltd | Wholesale & retail | 2025 |
| Overcliffe Mansions Management Company Limited | Households | 1987 |
| Overcomers Limited | Education | 2025 |
| Overcomers Outreach CIC | Education | 2025 |
| Overcomers Outreach Projects Ltd | Education | 2024 |
| Overcomers Outreach Trading CIC | Education | 2021 |
| Overseas Nepali Unity Forum-Uk Ltd | Other services | 2021 |
| Overseas Probate Service Limited | Administrative & support | 2005 |
| Owczarek & Malesa Properties Ltd | Real estate | 2021 |
| Owens & Porter Limited | Households | 2010 |
| Oxford 1964 Limited | Extraterritorial | 2014 |
| Oxford ESG Limited | Education | 2014 |
| Oxford International Students Services Ltd | Education | 2024 |
| Oxford Point Accountants Limited | Professional & scientific | 2026 |
| Oxford SA1 Limited | Real estate | 2018 |
| Oxford SA2 Limited | Real estate | 2018 |
| Oxford SA3 Limited | Real estate | 2018 |
| Oxford SA4 Limited | Real estate | 2018 |
| Oxford SA5 Limited | Real estate | 2018 |
| Oxford SA6 Limited | Real estate | 2018 |
| Oxford SA7 Limited | Real estate | 2018 |
| Oxford SA8 Limited | Real estate | 2018 |
| Oxford SA9 Limited | Real estate | 2018 |
| Oxfuture LLP | | 2023 |
| Oxraz Suites 1 Ltd | Real estate | 2019 |
| Oxraz Suites 2 Ltd | Real estate | 2019 |
| Oxraz Suites 3 Ltd | Real estate | 2019 |
| Oxsa Living Ltd | Real estate | 2019 |
| OY Electrical Ltd | Construction | 2022 |
| Oyster Bay Construction Limited | Construction | 2007 |
| OZD Trading Limited | Wholesale & retail | 2026 |
| Ozturk Compliance and Consulting Services Limited | Professional & scientific | 2020 |
| Ozuma Limited | Information & communication | 2012 |
| P & C Precision Limited | Professional & scientific | 2010 |
| P & L Properties Limited | Real estate | 1997 |
| P & L Property Maintenance Limited | Construction | 2001 |
| P & N Decorating Contractors Limited | Construction | 2001 |
| P & N Trading Limited | Hospitality | 2019 |
| P & R Construction South Limited | Construction | 2022 |
| P and S Clark Properties Limited | Real estate | 2013 |
| P F Parsons (Holdings) Ltd | Financial services | 2025 |
| P F Parsons Ltd | Construction | 1999 |
| P Haycroft Ltd | Construction | 2019 |
| P Higgins & Sons Limited | Manufacturing | 2014 |
| P J Andrews Holdings Limited | Administrative & support | 2016 |
| P J Andrews Limited | Extraterritorial | 2007 |
| P J Beaumont Associates Ltd | Administrative & support | 2016 |
| P R Stevens Limited | Real estate | 2011 |
| P T Solar Care Ltd | Manufacturing | 2023 |
| P Watson Fitness Ltd | Other services | 2021 |
| P Watson Rehabilitation Ltd | Health & social care | 2023 |
| P&G Civil Engineering Ltd | Construction | 2018 |
| P&P Food & Catering Ltd | Hospitality | 2025 |
| P&S Business Limited | Professional & scientific | 2023 |