| Oasis Consultancy Limited | Arts & recreation | 2003 |
| Occupy Ltd | Real estate | 2025 |
| Octa Developments Ltd | Construction | 2019 |
| Offsite Manufacturing Limited | Extraterritorial | 2017 |
| OH My COD ITS the Frying Squad Ltd | Hospitality | 2025 |
| Old Llanbradach Colliery Railway Sidings Regeneration Ltd | Construction | 2018 |
| Old Llanbradach Colliery Tier 4 Regeneration Ltd | Construction | 2018 |
| Old Llanbradach Regeneration (Group) Ltd | Construction | 2024 |
| Old Woolys Caerphilly Limited | Wholesale & retail | 2018 |
| Olsen and Lewis Services Limited | Construction | 2020 |
| ON the Ladder Property Group Ltd | Construction | 2024 |
| One Stop Pest Control Ltd. | Professional & scientific | 2013 |
| One Support Pass C.I.C. | Information & communication | 2025 |
| One-Stop Appliance Repairs Limited | Construction | 2021 |
| Ongl Design+Make Ltd | Professional & scientific | 2014 |
| Onsite Insights Global Limited | Other services | 2019 |
| ONTRACK365 Limited | Information & communication | 2017 |
| Open View Glazing Ltd | Construction | 2018 |
| Operation RTR Limited | Other services | 2013 |
| Optimize Consultancy Limited | Professional & scientific | 2013 |
| Opus Cleaning Consultants Ltd | Administrative & support | 2015 |
| Opus Remote Ltd | Wholesale & retail | 2017 |
| Opus Site Services Limited | Professional & scientific | 2023 |
| Osprey Lighting Limited | Arts & recreation | 2016 |
| Otfs Group Limited | Wholesale & retail | 2024 |
| Otherlands Publishing Ltd | Information & communication | 2023 |
| OUR Voice OUR Journey CIC | Education | 2025 |
| Outpace Accounting & Business Support Ltd | Professional & scientific | 2024 |
| Outride Distribution Ltd | Wholesale & retail | 2026 |
| Outride Projects Ltd | Professional & scientific | 2026 |
| Ozclean Limited | Administrative & support | 2018 |
| O’Connor Digital Ltd | Information & communication | 2022 |
| P & B Door & Window Maintenance Limited | Construction | 2003 |
| P & S Caravans Limited | Hospitality | 2012 |
| P & S Commercial Services Ltd | Professional & scientific | 2026 |
| P & T Woodruff Haulage Limited | Transport & logistics | 2013 |
| Pacific Developments (Wales) Limited | Wholesale & retail | 1978 |
| Padeladium Ltd | Arts & recreation | 2026 |
| Painted by ‘and Ltd | Construction | 2026 |
| Panayi Restaurants Limited | Hospitality | 2025 |
| Panda Education & Training Limited | Education | 2016 |
| Panda Electrical Limited | Construction | 2005 |
| Panwa Ideas Limited | Extraterritorial | 2016 |
| Paragon Management Associates Ltd | Professional & scientific | 2024 |
| Pareta Innovations Limited | Manufacturing | 2025 |
| Pariz Ltd | Real estate | 2025 |
| Parry Construction & Labour Limited | Construction | 2025 |
| Partners in Health (OH) Limited | Health & social care | 2011 |
| Pasc Developments Ltd | Construction | 2025 |
| Paternoster Consulting Ltd. | Information & communication | 2011 |
| Paul Davis Paediatrics Ltd | Health & social care | 2026 |
| Pavelin Properties Ltd | Real estate | 2021 |
| Peachleys Bakery Ltd | Wholesale & retail | 2020 |
| Peaknfly Limited | Wholesale & retail | 2025 |
| Pelvic Physiotherapy Limited | Health & social care | 2024 |
| Penfred Ltd | Real estate | 2025 |
| Pentwyn Developments Ltd | Real estate | 2020 |
| Penwisg Ltd | Wholesale & retail | 2019 |
| Penyrheol Barbers Ltd | Other services | 2025 |
| Penyrheol Fish Bar Ltd | Hospitality | 2019 |
| Perform Training Ltd | Arts & recreation | 2022 |
| Periculo Safety Group Ltd | Professional & scientific | 2019 |
| Personnel Hygiene Services Limited | Water & waste | 1963 |
| Peter's Food Service Limited | Manufacturing | 1997 |
| Peter's Holdings Limited | Professional & scientific | 2007 |
| Peter's Savoury Products Limited | Extraterritorial | 1997 |
| Peterson Plumbing and Heating Limited | Construction | 2026 |
| PGA Installations Ltd | Construction | 2026 |
| Phat Mods Ltd | Manufacturing | 2021 |
| Philwill Planning Consultancy Limited | Professional & scientific | 2018 |
| Phoenix Industrial Supplies Limited | Wholesale & retail | 2019 |
| PHS ALL Clear Limited | Professional & scientific | 1997 |
| PHS Bidco Limited | Financial services | 2014 |
| PHS Compliance Limited | Administrative & support | 1999 |
| PHS Group Limited | Other services | 2005 |
| PHS Holdings Limited | Financial services | 1999 |
| PHS Investments Limited | Professional & scientific | 1994 |
| PHS Services Limited | Financial services | 1999 |
| PHS Washrooms Limited | Professional & scientific | 2000 |
| PHS Wastekit Limited | Extraterritorial | 1973 |
| PHS Western Limited | Professional & scientific | 2001 |
| Picky Kelli Limited | Wholesale & retail | 2025 |
| PIN SIM Golf Ltd | Arts & recreation | 2026 |
| Pinnacle Industrial Roofing Supplies Limited | Construction | 2019 |
| Pipeworkers Limited | Wholesale & retail | 2006 |
| Pixelnest Studios Limited | Information & communication | 2025 |
| PJS Screeding Services Limited | Construction | 2013 |
| Plantopia Houseplants Ltd | Wholesale & retail | 2024 |
| Platinum Property Lettings Limited | Real estate | 2022 |
| Platinum Sky Travel Ltd | Administrative & support | 2018 |
| Plumb Tidy Ltd | Construction | 2019 |
| Plumbsave UK Limited | Wholesale & retail | 2006 |
| Plutus Consultancy Ltd | Professional & scientific | 2018 |
| PODS2HOMES CIC | Manufacturing | 2025 |
| Polaris Procurement and Consulting Limited | Administrative & support | 2013 |
| Poppelwood Community Hub Ltd | Arts & recreation | 2026 |
| Porset Drive Management Company Ltd | Real estate | 1993 |
| Portello Parts Ltd | Wholesale & retail | 2024 |
| Poshchair Medical Limited | Extraterritorial | 2005 |
| Powells Construction Limited | Construction | 2018 |