| Office Furniture Station Limited | Wholesale & retail | 2018 |
| Officeedge Limited | Manufacturing | 2025 |
| Offmore Court Residents Management Company Ltd | Households | 2022 |
| Offmore Road Garage Limited | Wholesale & retail | 2011 |
| OGS Consultants Ltd | Professional & scientific | 2019 |
| OH SEW Crafty Limited | Wholesale & retail | 2012 |
| OK Joinery Ltd | Manufacturing | 2014 |
| Olarra UK Limited | Wholesale & retail | 1981 |
| Old Court (Kidderminster) Management Limited | Households | 1987 |
| Old English Paving Ltd | Construction | 2018 |
| Old Forge Gardens Management Company Limited | Real estate | 2012 |
| Old Ravensworth Ltd | Construction | 2022 |
| Oleksyukore Ltd | Administrative & support | 2024 |
| OM Bingham Ltd | Administrative & support | 2021 |
| Omega SB Holdings Limited | Real estate | 2016 |
| Omega Steel Building Solutions Limited | Professional & scientific | 2010 |
| Omega Steel Buildings Ltd | Financial services | 2024 |
| Omegabalog Ltd | Transport & logistics | 2025 |
| Omegaslate (UK) Limited | Manufacturing | 1990 |
| Omegaslate Superseal Systems Limited | Manufacturing | 1997 |
| Omnibot Business Solutions Limited | Information & communication | 2025 |
| Omnis Tech Limited | Administrative & support | 2022 |
| ON Road Traffic Management Ltd | Construction | 2024 |
| On-Call Safety Systems Ltd | Construction | 2023 |
| ON247 Holdings Limited | Financial services | 2023 |
| ON247 Ltd | Information & communication | 2018 |
| ON247 SPV Limited | Real estate | 2025 |
| One Source Air & Energy Ltd | Construction | 2016 |
| Oneill Telecommunications Ltd | Information & communication | 2021 |
| Onhisnish Ltd | Transport & logistics | 2019 |
| Ontheglow Ltd | Information & communication | 2026 |
| Onyxwish Ltd | Wholesale & retail | 2019 |
| Oorbital AI Limited | Information & communication | 2026 |
| Opal Pharmacy Limited | Wholesale & retail | 2012 |
| Opportuna Limited | Professional & scientific | 2018 |
| Optimaclean Solutions Ltd | Administrative & support | 2025 |
| Optimum Therapy Ltd | Health & social care | 2016 |
| OQ Darby Ltd | Construction | 2022 |
| Oracleus Ltd | Hospitality | 2023 |
| Orange Orchid Ltd | Administrative & support | 2023 |
| Orangutan Studios Ltd | Manufacturing | 2022 |
| Orbital 4 Support Limited | Health & social care | 1999 |
| Orchard Close (the Damsons) Management Company Limited | Households | 2012 |
| Organic Everything Ltd | Wholesale & retail | 2015 |
| Original Products Ltd | Wholesale & retail | 2019 |
| Orion Business Ltd | Transport & logistics | 2021 |
| Ornamental Aquaculture Limited | Manufacturing | 2019 |
| Ornebhimzith Ltd | Administrative & support | 2024 |
| Ornzaerf Ltd | Administrative & support | 2024 |
| Ortomader Limited | Manufacturing | 2001 |
| Ostralish Ltd | Administrative & support | 2024 |
| OUR Jney Limited | Information & communication | 2025 |
| OUR Way Self Advocacy | Other services | 2002 |
| Outpost Custom Ltd | Professional & scientific | 2017 |
| Outreach Consultants Limited | Information & communication | 2022 |
| Ovancym Ltd | Administrative & support | 2024 |
| Ovenadium Ltd | Administrative & support | 2024 |
| Overthunk Limited | Professional & scientific | 2025 |
| Oviakrimz Ltd | Administrative & support | 2024 |
| Owen Kelly Properties Ltd | Real estate | 2026 |
| Oxy-H Ltd | Manufacturing | 2025 |
| OZA Construction Ltd | Construction | 2026 |
| Ozparts UK Limited | Wholesale & retail | 2020 |
| Ozzy Trims Ltd | Other services | 2026 |
| P and J Bennett Limited | Real estate | 2025 |
| P B Underhill Limited | Manufacturing | 2008 |
| P E Ashbrook Limited | Construction | 1998 |
| P J H Plumbing and Heating Ltd | Construction | 2023 |
| P Rogers Ltd | Construction | 2008 |
| P.G.S. Team Limited | Administrative & support | 2006 |
| P33 Limited | Construction | 2018 |
| Packatrix Studios Ltd | Transport & logistics | 2018 |
| Packwood Homes Limited | Construction | 2010 |
| PAI Cleaning Services Ltd | Administrative & support | 2025 |
| Paint & Glaze Limited | Manufacturing | 2024 |
| Painter Architects Limited | Professional & scientific | 2015 |
| Painters Law LLP | | 2019 |
| Painters Solicitors Limited | Professional & scientific | 2001 |
| Paisolutions Ltd | Wholesale & retail | 2024 |
| Palaysia UN Limited | Wholesale & retail | 2019 |
| Panache Administration Services Ltd | Administrative & support | 2014 |
| Panana UK Limited | Wholesale & retail | 2017 |
| Papershield Limited | Professional & scientific | 1999 |
| PAR Surveying & Building Services Limited | Construction | 2006 |
| Paradise Balti House Restaurant Limited | Hospitality | 2016 |
| Parador Group Limited | Health & social care | 2022 |
| Parcours Performance Coaching Limited | Administrative & support | 2019 |
| Pardoe Building Contractors Ltd | Construction | 2020 |
| Parkmore Chadwick Ltd | Financial services | 2006 |
| Partners in Business Limited | Professional & scientific | 2014 |
| Partsamesia Ltd | Transport & logistics | 2019 |
| Pash 2 Brothers Limited | Transport & logistics | 2023 |
| Pass-Time Furniture Ltd | Manufacturing | 2025 |
| Password Security Systems Limited | Administrative & support | 2012 |
| Pat-Man 24/7 Ltd | Construction | 2013 |
| Patio Door Specialists Limited | Manufacturing | 2002 |
| Pats Petals Limited | Wholesale & retail | 2026 |
| Paul Ashbrook Limited | Extraterritorial | 2001 |
| Paul Bate Construction Limited | Construction | 2004 |
| Paul Harding Tree Services Limited | Agriculture & fishing | 2015 |