| Optimustax Limited | Professional & scientific | 2012 |
| Optimy Ltd | Other services | 2014 |
| Options for Living Ltd | Health & social care | 2007 |
| Opus 3D Limited | Professional & scientific | 2019 |
| Opus Music Workshops Limited | Arts & recreation | 2002 |
| Opus Property Group Limited | Construction | 2018 |
| Orange Grove Gifts Ltd | Wholesale & retail | 2024 |
| Oratales Ltd | Information & communication | 2025 |
| Oravela Limited | Information & communication | 2017 |
| Orbb Properties Ltd | Real estate | 2026 |
| Orbiko Solutions Limited | Financial services | 2019 |
| Orca Events Ltd | Other services | 2022 |
| Orchard Arts Limited | Real estate | 2003 |
| Orchard House, Bath Limited | Hospitality | 2022 |
| Orchard Rentals Ltd | Real estate | 2017 |
| Orchard View Property Management Company Limited | Households | 2022 |
| Orchids by Celia Ltd | Agriculture & fishing | 2024 |
| Orchids Terrace Property Limited | Real estate | 2025 |
| Orci Clinical Consulting Limited | Health & social care | 2020 |
| Oreasco Limited | Construction | 2018 |
| Organic Nails CTP Ltd | Other services | 2025 |
| Organized Minds Ltd | Education | 2024 |
| Orial Chip Designs Limited | Professional & scientific | 2011 |
| Oriani and Co London Ltd | Professional & scientific | 2018 |
| Original Group Holding Limited | Real estate | 2020 |
| Orion Infrastructure Advisors Limited | Professional & scientific | 2023 |
| Orion People Development Ltd | Professional & scientific | 2018 |
| Ormonde House (Bath) Management Company Limited | Households | 1976 |
| Orpheus Corporation Limited | Professional & scientific | 1988 |
| Orrani Consulting Limited | Professional & scientific | 2003 |
| Orson and Welles Limited | Wholesale & retail | 2013 |
| Orthoscape Ltd | Manufacturing | 2022 |
| Orwen Properties Ltd | Real estate | 2026 |
| ORX UK Limited | Financial services | 2009 |
| Orxia Ltd | Professional & scientific | 2021 |
| Oryn Ltd | Financial services | 2025 |
| Osato Chemicals & Engineering Ltd | Manufacturing | 2022 |
| Osborne (Buxton) Limited | Construction | 1997 |
| Osborne Pike EOT Limited | Professional & scientific | 2025 |
| Osborne Pike Limited | Administrative & support | 2002 |
| Osborne Tennis Ltd | Arts & recreation | 2023 |
| Oscar Holdings Limited | Real estate | 2005 |
| Oscar Martinez Limited | Professional & scientific | 2024 |
| Osteo & Physio Taunton Ltd | Health & social care | 2023 |
| Osteobath Ltd | Health & social care | 2019 |
| Osteria Partenopea Bath Ltd | Hospitality | 2025 |
| OSU Growth Ltd | Administrative & support | 2026 |
| Other Important Matters Limited | Administrative & support | 2006 |
| Otway and Davenport Properties Limited | Construction | 2021 |
| OUR Club House CIC | Hospitality | 2025 |
| OUR House AP Ltd | Education | 2024 |
| OUR Name IS MUD Ltd | Information & communication | 2013 |
| Ouros Consulting Ltd | Professional & scientific | 2025 |
| OUT of the Ordinary FX Ltd | Information & communication | 2025 |
| Outfits Live on Ltd | Wholesale & retail | 2024 |
| Outlaw Strategy Limited | Professional & scientific | 2018 |
| Outside-In Consultancy Limited | Professional & scientific | 2026 |
| Outsourced Branding Ltd | Administrative & support | 2020 |
| Outwith Limited | Professional & scientific | 2017 |
| Oval (1115) Limited | Extraterritorial | 1996 |
| Oval Subsidiary 2 Limited | Information & communication | 2016 |
| Oval Subsidiary 3 Limited | Financial services | 2022 |
| Oval Subsidiary 4 Limited | Information & communication | 2011 |
| OVO Solutions Ltd | Administrative & support | 2014 |
| Owan Group Limited | Wholesale & retail | 2024 |
| Owen Spafford & Louis Campbell LLP | | 2024 |
| Owls Nest Shoot Ltd | Other services | 2021 |
| Oxbrock Ltd | Real estate | 2022 |
| Oxcombe Ltd | Agriculture & fishing | 2020 |
| Oxegene Limited | Extraterritorial | 2016 |
| Oxford Associates Limited | Information & communication | 2013 |
| Oxford Health and Medical Ltd | Health & social care | 2023 |
| Oxinet Limited | Information & communication | 2003 |
| Oxmedchem Consulting Ltd | Professional & scientific | 2017 |
| Oztekin Plasterer & Paint Ltd | Construction | 2021 |
| P & a Bowen Ltd | Financial services | 2024 |
| P Blackwell Developments Ltd | Construction | 2012 |
| P D Allen Haulage Limited | Transport & logistics | 2008 |
| P G Building & Construction Ltd | Construction | 2014 |
| P Howell & Sons Plastering Limited | Construction | 2023 |
| P J Lintern and SON Limited | Wholesale & retail | 2006 |
| P M Property Services (Wessex) Ltd | Real estate | 2011 |
| P W Foster Limited | Health & social care | 2001 |
| P W Masonry Limited | Construction | 2010 |
| P Walker Engineering Limited | Construction | 2009 |
| P Walker Property Limited | Real estate | 2024 |
| P&E Window Cleaning Services Ltd | Administrative & support | 2025 |
| P&M Medical Consultancy Limited | Health & social care | 2023 |
| P&S Magenent Ltd | Real estate | 2025 |
| P.C.P. Micro Products (DEV) Limited | Arts & recreation | 1993 |
| P.C.P. Micro Products Limited | Manufacturing | 1982 |
| P.G.C. (South West) Limited | Construction | 2017 |
| P.M. Bines Limited | Wholesale & retail | 2007 |
| Pacific Dynamic Limited | Extraterritorial | 2012 |
| PAD Enterprises Ltd | Real estate | 2020 |
| Paddock Properties Ltd | Construction | 2014 |
| Paddocks Edge LLP Ltd | Hospitality | 2024 |
| Padfield Holdings Limited | Professional & scientific | 2007 |
| Padstone AI Ltd | Information & communication | 2026 |
| Paikard Ltd | Wholesale & retail | 2025 |