| Opilat Ltd | Other services | 2019 |
| Opjem Ltd | Real estate | 2018 |
| Oppolis Software Limited | Information & communication | 2003 |
| Oppsport Software Limited | Information & communication | 2011 |
| Optimal Tutors Limited | Education | 2013 |
| Optimus Resource Management Ltd | Professional & scientific | 2022 |
| Opulence Endeavours Ltd | Information & communication | 2022 |
| Opulence Endeavours Property Ltd | Hospitality | 2025 |
| Opulent Travel Services Limited | Administrative & support | 2016 |
| Oracle Advertising Limited | Professional & scientific | 2002 |
| Oraculum Consulting Limited | Professional & scientific | 2023 |
| Orbem Electrical Limited | Construction | 2023 |
| Orbem Limited | Construction | 2023 |
| Orbitra Ltd | Information & communication | 2025 |
| Ordabasy Ltd | Other services | 2020 |
| Order of the Blade Ltd | Administrative & support | 2020 |
| Orente Ltd | Other services | 2022 |
| Organic Molecule Ltd | Wholesale & retail | 2019 |
| Organic Wild Limited | Wholesale & retail | 2019 |
| Orian Investment Group Ltd | Real estate | 2023 |
| Orient Light Haulage Limited | Information & communication | 1988 |
| Origin Architects Limited | Professional & scientific | 2000 |
| Original Mobiles New Lcds & Parts Limited | Wholesale & retail | 2011 |
| Orihuna Ltd | Other services | 2019 |
| Ormlex Ltd | Other services | 2019 |
| Ornasy Ltd | Other services | 2019 |
| Orouji Global Holding Ltd | Wholesale & retail | 2025 |
| Orush Medics Limited | Health & social care | 2012 |
| OS Phoenix Acquisition Limited | Financial services | 2018 |
| OS Phoenix Bidco Limited | Financial services | 2017 |
| OS Phoenix Holdco Limited | Financial services | 2017 |
| OS Phoenix Midco Limited | Financial services | 2017 |
| OS Prime Developments Limited | Real estate | 2026 |
| Oscars (Wales) Limited | Wholesale & retail | 2004 |
| Osco International Limited | Wholesale & retail | 1988 |
| OSD Testing Solutions Ltd | Information & communication | 2023 |
| Osetik Ltd | Other services | 2019 |
| Osiks Limited | Wholesale & retail | 2025 |
| OSL Financial Services Ltd | Financial services | 2008 |
| Osteopathy Plus Shropshire Ltd | Health & social care | 2018 |
| Osters Ltd | Other services | 2019 |
| Otepaa Ltd | Other services | 2019 |
| Other Peoples Data Limited | Information & communication | 2009 |
| OTI Trans Ltd | Transport & logistics | 2024 |
| OTT Exterior Cleaning Ltd | Administrative & support | 2025 |
| Ottar Ltd | Real estate | 2025 |
| OUR Pet Friends Ltd | Wholesale & retail | 2019 |
| OUTBACK2BASICS Ltd | Education | 2015 |
| Outlook Training Services Ltd | Education | 2023 |
| Overpowered Gaming Ltd | Information & communication | 2006 |
| OVM Solutions Ltd | Transport & logistics | 2018 |
| Owens & Co Limited | Professional & scientific | 2011 |
| Owens & Owens Holdings Ltd | Other services | 2024 |
| Owens Property Maintenance Limited | Real estate | 2026 |
| Owensboro Ltd | Wholesale & retail | 2022 |
| Owerit Ltd | Other services | 2019 |
| Ownya Care Limited | Hospitality | 2024 |
| Oxford Bookkeeping Ltd | Professional & scientific | 2006 |
| Oxford ST Store Ltd | Wholesale & retail | 2025 |
| Oxon Dental Care Ltd | Health & social care | 2010 |
| Oyoo Foods Limited | Hospitality | 2025 |
| OZ Events Limited | Hospitality | 2024 |
| Ozama Ltd | Administrative & support | 2018 |
| Ozyureks Property Ltd | Real estate | 2020 |
| P & B Holdings Limited | Professional & scientific | 2006 |
| P & H Design Engineering Ltd | Manufacturing | 2012 |
| P & H Eggs Limited | Wholesale & retail | 2005 |
| P a B Cars Ltd | Wholesale & retail | 2021 |
| P and MW Holding Ltd | Health & social care | 2023 |
| P C & I O Management Ltd | Administrative & support | 2006 |
| P C S Light Couriers Ltd | Transport & logistics | 2026 |
| P E Roberts Limited | Professional & scientific | 2010 |
| P J Coupland Plumbing & Heating Limited | Construction | 2006 |
| P Johnson Plant Limited | Construction | 2017 |
| P N Weston Ltd | Real estate | 2018 |
| P S Chaudhari Limited | Real estate | 2013 |
| P T Harrison Limited | Professional & scientific | 2010 |
| P Weston Ltd | Real estate | 2022 |
| P&J Midlands Ltd | Hospitality | 2021 |
| P&P Recruitment Group Ltd | Administrative & support | 2026 |
| P. J. Jeffrey Holdings Ltd | Real estate | 2023 |
| P.8. Holdings Ltd | Professional & scientific | 2016 |
| P.D. Carpentry Ltd | Construction | 2003 |
| P.J.Luckman Ltd | Other services | 2004 |
| P.J.M. Holdings (Shropshire) Ltd | Financial services | 2020 |
| P.Leek Commercial Repairs Limited | Wholesale & retail | 2003 |
| P.M.H. Vehicle Equipment Limited | Wholesale & retail | 2008 |
| P.P. & P.D. Taylor Limited | Other services | 2008 |
| P.T. Holdco. Limited | Information & communication | 2017 |
| P.T. Products Contractors Limited | Construction | 2013 |
| P1 Accounting Services Ltd | Professional & scientific | 2013 |
| P1 Aquatics Ltd | Agriculture & fishing | 2025 |
| P1 Cleaning Services Ltd | Administrative & support | 2022 |
| P1 Finance Services Ltd | Financial services | 2017 |
| P1 Financial Services Ltd | Financial services | 2017 |
| P1 Management Consultancy Ltd | Professional & scientific | 2023 |
| P1 Retail Ltd | Wholesale & retail | 2020 |
| P600 Mountaineering Limited | Education | 2013 |
| PA Training Services Limited | Information & communication | 2011 |
| Paca Ltd | Transport & logistics | 2019 |