| OB Assistance Limited | Real estate | 2020 |
| Obamedo Foods Limited | Wholesale & retail | 2023 |
| OCA Developments Ltd | Construction | 2024 |
| Ocean Palace Ltd | Hospitality | 2019 |
| Odie FPS Ltd | Financial services | 2017 |
| OG Ventures Limited | Administrative & support | 2024 |
| Ohana Childcare Limited | Health & social care | 2023 |
| Ohmania Ltd | Information & communication | 2013 |
| Old Brook View Residents Management Company Limited | Households | 2024 |
| Old Church Court Management Services Limited | Households | 2015 |
| Old Decorating Contractors Ltd | Construction | 2025 |
| Old Farm Block a Management Limited | Households | 1988 |
| Old Farm Block D Management Limited | Households | 1988 |
| Old Farm Blocks B and C Management Limited | Households | 1988 |
| Old Highway Consulting Limited | Administrative & support | 2014 |
| Old Kiln Lessees Limited | Households | 2004 |
| Old Montague Freehold Company Limited | Households | 2003 |
| Old Oaks Management Company Limited | Households | 1988 |
| Old Road (Churwell) Management Company Limited | Households | 2003 |
| Old Thorne Road (NO. 1) Management Company Limited | Households | 2008 |
| Old Thorne Road (NO.2) Management Company Limited | Households | 2008 |
| Oldfield Park (Poulton) Management Company Limited | Households | 2017 |
| Oliver Hayden Limited | Wholesale & retail | 2011 |
| Oliver's Bridal & Formalwear Ltd. | Wholesale & retail | 2015 |
| Omchug Ltd | Manufacturing | 2015 |
| Omidos Limited | Professional & scientific | 2003 |
| Omnivoice Communications Ltd | Professional & scientific | 2025 |
| ON the Mark Trading Ltd | Transport & logistics | 2023 |
| One Hundred Commercial Limited | Construction | 2019 |
| One Hundred Property Group Limited | Real estate | 2014 |
| One Hyde Park Street Freehold Limited | Households | 2013 |
| One London Developments Limited | Construction | 2014 |
| One Step Construction Staffing Limited | Administrative & support | 2024 |
| Onestopspecial Ltd | Wholesale & retail | 2019 |
| Online Hardware Direct Ltd | Information & communication | 2013 |
| Only Stone Ltd | Extraterritorial | 2022 |
| Ontoolz Ltd | Information & communication | 2019 |
| Open Herts Therapy Limited | Public administration | 2023 |
| Optimum Real Estate Limited | Real estate | 2016 |
| Optimum Residential Properties Ltd | Real estate | 2021 |
| Optiview Ltd | Administrative & support | 2025 |
| Opto Talent Ltd | Other services | 2023 |
| Opulent Reign Ltd | Wholesale & retail | 2018 |
| Orange Panda Claims Services Limited | Professional & scientific | 2020 |
| Oray Tasci Ltd | Professional & scientific | 2019 |
| Orchard Apartments (Harlow) Ltd | Households | 2014 |
| Orchard U.K. Limited | Real estate | 2021 |
| Originails UK Limited | Other services | 2021 |
| Original Bathrooms Limited | Wholesale & retail | 1981 |
| Original Gravity Records Ltd | Wholesale & retail | 2002 |
| Orlando's Autos Ltd | Wholesale & retail | 2025 |
| Orsett Village Residents Association Limited | Households | 2004 |
| Orton Copse (Peterborough) Management Company Limited | Households | 2023 |
| Orwell Court (South Oxhey) Management Company Limited | Households | 1984 |
| Osborne Mews (Allbrook) Management Company Limited | Households | 2006 |
| Osteria Dante Limited | Hospitality | 2008 |
| Otterstye View Management Company Limited | Households | 2013 |
| OUR Time IS NOW Ltd | Other services | 2026 |
| OUT the Box Sports Limited | Arts & recreation | 2024 |
| Outcome Services for Public Sector Limited | Information & communication | 2020 |
| Outdoor Food Solutions Limited | Hospitality | 2007 |
| Outrospect Limited | Professional & scientific | 2017 |
| Over/Shadow Limited | Arts & recreation | 2018 |
| Overland Outfitters UK Ltd | Manufacturing | 2023 |
| Overton House (Frodsham) Management Company Limited | Households | 2005 |
| Oviraf UK Logistic Ltd | Transport & logistics | 2025 |
| Owens Event Kitchen Ltd | Hospitality | 2023 |
| OWL Advisory Limited | Professional & scientific | 2018 |
| Oxford AVE (Harlington) Management Company Limited | Households | 2005 |
| OZ International Trade Ltd | Wholesale & retail | 2022 |
| OZE Industry Limited | Manufacturing | 2021 |
| P J Davidson (UK) Limited | Construction | 2018 |
| P J W Building Services Limited | Construction | 2023 |
| P J W Contractors Limited | Construction | 2003 |
| P S Brown Limited | Information & communication | 2012 |
| P. K. P. Investments Ltd | Real estate | 2021 |
| P.S.V. Transport Systems Limited | Manufacturing | 1994 |
| Pace Eco & Solar Limited | Construction | 2023 |
| Pace Projects & Developments Limited | Construction | 2021 |
| Pace Projects Limited | Construction | 2025 |
| Padalino Investments Limited | Real estate | 2023 |
| Padel & Batt Ltd | Other services | 2018 |
| Padel Time Sports Club (Wormley) Ltd | Arts & recreation | 2025 |
| Page Mews Management Ltd | Households | 2012 |
| Pages Priory (Leighton Buzzard) Management Company Limited | Households | 2006 |
| Paine Roofing Specialists Ltd | Construction | 2025 |
| Palermo Health Limited | Wholesale & retail | 2025 |
| Paliadon Investments Ltd | Construction | 2013 |
| Palle Moeller Foundation | Health & social care | 1990 |
| Palliative Solutions Limited | Other services | 2012 |
| Palm Tree Thai Spa Ltd | Other services | 2021 |
| Palmerston Grove (Osterley) Management Company Limited | Households | 1998 |
| Panache for Kids Holdings Ltd | Financial services | 2021 |
| Panache for Kids Ltd | Wholesale & retail | 2014 |
| Pannal Hall Farm Residents Management Company Limited | Households | 2004 |
| Pantocrator Limited | Financial services | 2025 |
| Papadam Studios Limited | Construction | 2015 |
| Paragon Star Ltd | Wholesale & retail | 2019 |
| Paramount Healthcare Group Limited | Financial services | 2025 |
| Parc Jasmin Apartment Residents Management Company Limited | Households | 2018 |