| Operational Compliance Systems Ltd | Information & communication | 2023 |
| Opex Consulting Ltd | Professional & scientific | 2010 |
| Opex FIX Ltd | Information & communication | 2026 |
| OPM Groundworks Ltd | Construction | 2025 |
| Opschain Limited | Information & communication | 2019 |
| Optima Psychology Limited | Education | 2006 |
| Opus Agencies Limited | Agriculture & fishing | 1993 |
| Opus International Holdings Limited | Financial services | 2020 |
| Opus International Products Limited | Professional & scientific | 2013 |
| Opus Space Technologies Limited | Professional & scientific | 2022 |
| Orange Property Investments Limited | Real estate | 2025 |
| Orascan Limited | Health & social care | 2020 |
| ORB Holdings & Investments Ltd | Real estate | 2021 |
| ORB Quantum Consulting Limited | Professional & scientific | 2006 |
| Orbital PEO Ltd | Professional & scientific | 2025 |
| Orchard Corner Ltd | Wholesale & retail | 2022 |
| Orenda Holdings Limited | Financial services | 2020 |
| Organisation & People Development Limited | Professional & scientific | 1984 |
| Organise Your Life Ltd | Public administration | 2023 |
| Organized Play Events Limited | Administrative & support | 2020 |
| Orica Prototyping Ltd | Manufacturing | 2026 |
| Original Equipment Limited | Wholesale & retail | 2026 |
| Orion Cleaning Company Limited | Administrative & support | 1987 |
| Orion Management Solutions Ltd | Professional & scientific | 2020 |
| ORO Verde Coffees Ltd | Wholesale & retail | 2025 |
| Orthodontic Team Training Limited | Administrative & support | 2010 |
| Orthodontics Group Ltd | Extraterritorial | 2018 |
| Orthoedu Consultancy Ltd | Education | 2024 |
| Orthoral Limited | Health & social care | 2018 |
| Orthovision Limited | Health & social care | 2014 |
| OS Global Trade Limited | Wholesale & retail | 2025 |
| OSC Taxis Ltd | Transport & logistics | 2023 |
| Oscar Homes Limited | Construction | 2014 |
| OT Assist Ltd | Health & social care | 2023 |
| OTG Electrical Ltd | Manufacturing | 2024 |
| Other Call Limited | Administrative & support | 2007 |
| Otta International Limited | Manufacturing | 2014 |
| OUR Building Contract Ltd | Construction | 2026 |
| OUR Neutral Ground Limited | Information & communication | 2023 |
| Outreach Properties Limited | Real estate | 1972 |
| Overhead Line Services Limited | Transport & logistics | 2019 |
| OVR Culture Limited | Professional & scientific | 2024 |
| Owen & Co UK Ltd | Administrative & support | 2025 |
| Owen Stephens Consulting Ltd | Professional & scientific | 2014 |
| OWL & Rose Limited | Hospitality | 2022 |
| Owlet Press Ltd | Wholesale & retail | 2019 |
| Oxford Court Property Management Company Limited | Households | 1992 |
| Oxford Cyber Risk Advisory Ltd | Information & communication | 2024 |
| Oxlon Ltd | Information & communication | 2025 |
| Oxygen Graphics Limited | Manufacturing | 2013 |
| OYA Energy UK Limited | Construction | 2021 |
| OZ Digital Solutions Ltd | Information & communication | 2019 |
| O’Brien Developments Dartmouth Fish Hoek Limited | Construction | 2016 |
| O’Brien Developments Dartmouth Waterside Limited | Construction | 2016 |
| O’Brien Holdings 2020 Limited | Financial services | 2020 |
| P & K Property Holdings Limited | Real estate | 2021 |
| P a BEE Ltd | Transport & logistics | 2011 |
| P J Brickwork Limited | Construction | 2012 |
| P S Brown Consult Ltd | Professional & scientific | 2020 |
| P&H Group Ltd | Real estate | 2024 |
| P&N True Care Limited | Administrative & support | 2025 |
| P&S Carpentry Ltd | Manufacturing | 2019 |
| P&S Property Renovations Ltd | Construction | 2021 |
| P.A.Hopkins Limited | Real estate | 1959 |
| P.I. Construct Ltd | Other services | 2014 |
| P.L. Carbodies Limited | Professional & scientific | 2005 |
| P.L.P. Investments Limited | Construction | 1990 |
| P.W. Maddock Associates Ltd | Information & communication | 2017 |
| P3OPLE Ltd | Professional & scientific | 2018 |
| Pachyderm House Ltd | Hospitality | 2025 |
| Paddlebrook Limited | Agriculture & fishing | 2024 |
| Padmore Management Company Limited | Real estate | 1981 |
| Page Residential Investments Limited | Real estate | 2020 |
| Paintstore Limited | Wholesale & retail | 1990 |
| Palana Limited | Information & communication | 1996 |
| Palladium Law Limited | Professional & scientific | 2020 |
| Pallet Distribution Ltd | Wholesale & retail | 2017 |
| Palmer Hargreaves (UK) Limited | Professional & scientific | 1996 |
| Palmer Hargreaves Holdings Limited | Professional & scientific | 2008 |
| Palmer Hargreaves Limited | Professional & scientific | 1983 |
| Palmgrange Limited | Health & social care | 1981 |
| Panda Mortgage Services Limited | Financial services | 2018 |
| Pandit Test Delivery Consulting Limited | Professional & scientific | 2026 |
| Panesar Investment Estates Limited | Construction | 2019 |
| Panesars Estates Limited | Real estate | 2019 |
| Pangaea Sculptors' Centre Community Interest Company | Arts & recreation | 2013 |
| Panino Head Ltd | Hospitality | 2025 |
| Pantheon Performance Ltd | Wholesale & retail | 2023 |
| Papa Khan’S Pizza Ltd | Hospitality | 2023 |
| Paper Sales (WKS) Ltd | Administrative & support | 2016 |
| PAR 72 Ltd | Professional & scientific | 2000 |
| Paradise Renovations Ltd | Households | 2020 |
| Parallel Insights Limited | Professional & scientific | 2015 |
| Paramex Digital Limited | Information & communication | 2018 |
| Paramex Limited | Information & communication | 2000 |
| Paramount Property Partners Limited | Real estate | 2023 |
| Parctec Ltd | Information & communication | 2026 |
| Park IT Savvy Ltd | Administrative & support | 2026 |
| Parker Care Services Limited | Health & social care | 2022 |
| Parker's Security Limited | Manufacturing | 2024 |