| OEG Marine Group Limited | Financial services | 2019 |
| OEG Marine Limited | Administrative & support | 2013 |
| OEG Midco 1 Limited | Financial services | 2023 |
| OEG Midco 2 Limited | Financial services | 2023 |
| OEG Offshore Group Limited | Mining & quarrying | 2008 |
| OEG Parentco Limited | Financial services | 2023 |
| OEG Renewables Blades Limited | Manufacturing | 2023 |
| OEG Renewables Group Limited | Financial services | 2023 |
| OEG Renewables Limited | Administrative & support | 2006 |
| OEG Topco Limited | Financial services | 2023 |
| OEG Training Limited | Construction | 2010 |
| OES Oilfield Services (UK) Limited | Mining & quarrying | 2006 |
| Offshore Drone Co Limited | Administrative & support | 2018 |
| Offshore Homes Ltd | Hospitality | 2025 |
| Offshore Marine Contractors Limited | Mining & quarrying | 1991 |
| Offshore Structural Systems Ltd | Construction | 2026 |
| Ogbanufe Offshore Services Limited | Mining & quarrying | 2014 |
| Ohana Mortgages Ltd | Financial services | 2024 |
| Oilfield Containers Limited | Mining & quarrying | 2007 |
| Oilfield Energy Services Ltd | Mining & quarrying | 2017 |
| OILS4LIFE Limited | Wholesale & retail | 2003 |
| OILS4LIFE Therapy Limited | Other services | 2019 |
| Ojlg Ltd | Professional & scientific | 2025 |
| OJS Fibreglassing Limited | Manufacturing | 2025 |
| Okspar Freight Ltd | Transport & logistics | 2023 |
| Olave Properties Limited | Real estate | 2015 |
| Oleja Construction Ltd | Construction | 2024 |
| Olitemga Ltd | Wholesale & retail | 2024 |
| Olivers Software Company Limited | Information & communication | 2004 |
| Olmettimarketing Ltd | Professional & scientific | 2022 |
| OML Services Limited | Real estate | 1979 |
| ON the HUH Productions Ltd | Information & communication | 2024 |
| ON Top Brickwork Ltd | Construction | 2026 |
| ON Track Autos Ltd | Wholesale & retail | 2023 |
| On-Top Roofing Norfolk Limited | Construction | 2021 |
| On-Your-Side Norfolk Ltd. | Education | 2021 |
| One to One Home Care Agency Limited | Health & social care | 2001 |
| Onestopintensives Ltd | Education | 2022 |
| Online KHW Shop Ltd | Wholesale & retail | 2025 |
| Online Mobiles Limited | Professional & scientific | 2016 |
| Onlyfinance Limited | Professional & scientific | 2024 |
| Onrg Limited | Professional & scientific | 2014 |
| Onyx Coatings and Services Limited | Manufacturing | 2024 |
| Operis Ltd | Mining & quarrying | 2025 |
| Opority Ltd | Information & communication | 2024 |
| OPS Group Holdings Ltd | Financial services | 2016 |
| OPS Training Ltd | Education | 2016 |
| OPS Wind Ltd | Manufacturing | 2021 |
| Optem Limited | Professional & scientific | 2015 |
| Optimal Plant Solutions Ltd | Professional & scientific | 2022 |
| Optimal Safety Solutions Ltd | Wholesale & retail | 2025 |
| Optimum Rent Ltd | Construction | 2009 |
| Optimum Residence Ltd | Real estate | 2026 |
| Opus Inspection Services Ltd | Mining & quarrying | 2018 |
| Orange Store P Ltd | Wholesale & retail | 2025 |
| Orbital Freight Limited | Transport & logistics | 1989 |
| Orhan Investments Ltd | Hospitality | 2019 |
| Oriental Tastes Ltd | Wholesale & retail | 2019 |
| Origin Hope Media Group Ltd | Information & communication | 2019 |
| Ormesby Manor Limited | Hospitality | 2014 |
| Orthoactive Limited | Health & social care | 2010 |
| Osborn and Woods Limited | Construction | 2005 |
| Osborne Energy Services Limited | Mining & quarrying | 2017 |
| OSM Aviation Ltd | Transport & logistics | 2025 |
| Othello Taverna Limited | Hospitality | 2014 |
| OTO Radiography Practise Ltd | Health & social care | 2024 |
| Oulton Broad Building Services Limited | Construction | 2018 |
| OUR Family Tree Limited | Real estate | 2020 |
| Outdoor Value Limited | Arts & recreation | 2008 |
| Outdoor Value Retail Limited | Administrative & support | 2008 |
| Outdoor Value Trustee Limited | Financial services | 2025 |
| OUTLET4YOU Ltd | Wholesale & retail | 2021 |
| Ovamill Limited | Construction | 2005 |
| Owlidex Group Ltd | Administrative & support | 2025 |
| Oxcel Ltd | Agriculture & fishing | 2022 |
| Oxford Hotel Investments Ltd | Hospitality | 2023 |
| P & RH Properties Limited | Real estate | 2026 |
| P & S Care & Support Services Limited | Administrative & support | 2024 |
| P & S Energy Limited | Administrative & support | 2025 |
| P & S Howlett Limited | Wholesale & retail | 2015 |
| P & S Personnel Services Limited | Administrative & support | 2006 |
| P & S Rail & Infrastructure Limited | Administrative & support | 2025 |
| P & S Recruitment Limited | Administrative & support | 2025 |
| P Arnold Electrical Ltd | Information & communication | 2013 |
| P E Roos Limited | Health & social care | 2017 |
| P G Cater Builders Limited | Construction | 2007 |
| P H Starling Limited | Agriculture & fishing | 2004 |
| P J Waters Engineering Limited | Professional & scientific | 2023 |
| P Robotham Building Services Limited | Construction | 2007 |
| P&W Fabrication Ltd | Other services | 2017 |
| P&W Renovations Limited | Construction | 2022 |
| P.A. Brooks Plastering Limited | Construction | 2006 |
| P.C.M. Design & Computing Limited | Professional & scientific | 1998 |
| P.E.S. Renewables Ltd | Construction | 2022 |
| P.J.P.Dunbar Limited | Construction | 1963 |
| P.K Supermarket Limited | Wholesale & retail | 2021 |
| P.K.A. Developments Limited | Real estate | 1988 |
| P.S Electrotech Ltd | Manufacturing | 2020 |
| PAD Thai Bangkok Restaurant and Takeaway Ltd | Hospitality | 2023 |
| Paddy Hall Presentations Limited | Arts & recreation | 1999 |