| Orchard Street Management Limited | Households | 2005 |
| Order 66 Ltd | Construction | 2017 |
| Orebam Home & Property Refresh Ltd | Administrative & support | 2026 |
| Oreofe Healthcare Limited | Health & social care | 2019 |
| Orgrow Limited | Professional & scientific | 2023 |
| Orie Solutions Limited | Transport & logistics | 2012 |
| Orinya Medical Service Ltd | Health & social care | 2026 |
| Orisun Praxis Advisory Ltd | Professional & scientific | 2026 |
| Orizone Ltd | Health & social care | 2022 |
| Orizzonte Clinical Research Ltd | Professional & scientific | 2024 |
| Ornan Elevatexpress Ltd | Manufacturing | 2026 |
| Orpheon Property Limited | Real estate | 2024 |
| Orpheus Gallery Art Ltd | Wholesale & retail | 2025 |
| Orson Property Ltd | Real estate | 2025 |
| Orthodent Ltd | Health & social care | 2008 |
| OSA Consults Limited | Health & social care | 2024 |
| Osagbai Eriki Limited | Health & social care | 2025 |
| Osarogie Medical Service Limited | Health & social care | 2025 |
| Osas Medical Service Ltd | Health & social care | 2024 |
| Oscar Handyman Limited | Construction | 2013 |
| Oscar Management Services Limited | Professional & scientific | 2026 |
| Oscar Scientific Limited | Information & communication | 2019 |
| OSE Bolt Limited | Health & social care | 2024 |
| Osidaniels Ltd | Information & communication | 2020 |
| Osidge Park Management Company Ltd | Households | 2012 |
| OSK Technology & Consulting Ltd | Professional & scientific | 2025 |
| Osoba-Eml Limited | Health & social care | 2024 |
| Osoj Limited | Real estate | 2021 |
| Ospro Ltd | Real estate | 2019 |
| Osumilite Limited | Wholesale & retail | 2021 |
| Osuolale Idowu Ventures Limited | Real estate | 2016 |
| OUBAS9 Limited | Professional & scientific | 2022 |
| OUR Lady of Fatima Catholic Multi Academy Trust | Education | 2011 |
| OUR Transport Limited | Transport & logistics | 2019 |
| Ourania Project Management Ltd | Professional & scientific | 2022 |
| Outbound Hub UK Ltd | Information & communication | 2023 |
| Outbound Property Holdings Limited | Real estate | 2024 |
| Outbound Solutions Group Ltd | Information & communication | 2023 |
| Outbound Virtual UK Ltd | Information & communication | 2023 |
| Outperform Group Limited | Administrative & support | 2024 |
| Outsdrz CIC | Other services | 2026 |
| Oven Cleaning London Ltd | Administrative & support | 2013 |
| Ovenden Papers Limited | Wholesale & retail | 1943 |
| Ovendens UK Limited | Wholesale & retail | 2013 |
| Over Gravity Gymnastics Ltd | Arts & recreation | 2018 |
| OVI Trans Ltd | Transport & logistics | 2025 |
| Ovidiu Consulting Services Ltd | Professional & scientific | 2020 |
| Ovronnaz Commercial Services Limited | Administrative & support | 2020 |
| OVY Logistics Ltd | Transport & logistics | 2015 |
| Owczarcars Ltd | Transport & logistics | 2024 |
| Owen Shiro Limited | Health & social care | 2019 |
| Owls Close Management Company Limited | Households | 1991 |
| Oxford Ellis Holdings Ltd | Real estate | 2024 |
| Oxford Universal Consultants Ltd | Construction | 2021 |
| Oxiavibe Ltd | Wholesale & retail | 2026 |
| Oxygne Media Limited | Information & communication | 2026 |
| Oylase Limited | Wholesale & retail | 2025 |
| Oztum Investment Ltd | Real estate | 2020 |
| P & L Signs Limited | Manufacturing | 2008 |
| P & O Investments Limited | Real estate | 2024 |
| P & P Homes Ltd | Real estate | 2012 |
| P a Pickering Developments Limited | Real estate | 2023 |
| P and L Vacuums Ltd | Manufacturing | 2019 |
| P J Apinya Limited | Other services | 2017 |
| P J Conveyancing Limited | Other services | 2020 |
| P S Hayden Fencing Ltd | Administrative & support | 2023 |
| P T Barnes Construction Consultants Limited | Construction | 2007 |
| P&C Rentals U.K. Ltd | Real estate | 2023 |
| P&J Oynx Holdings Ltd | Financial services | 2025 |
| P&M (UK) Ltd | Construction | 2014 |
| P.W.May Contracting Ltd | Agriculture & fishing | 2009 |
| P1 Manufacturing and Kitting Solutions Limited | Manufacturing | 2023 |
| P2PFOOTBALLACADEMY Ltd | Arts & recreation | 2023 |
| P73 Apparel Ltd | Wholesale & retail | 2019 |
| Pace Precision Engineering LLP | | 2010 |
| Pace Precision Limited | Manufacturing | 2010 |
| Packington Hall Estate Management Company Limited | Households | 2021 |
| Packington Hall Freehold Management Company Limited | Households | 2021 |
| Packington Street Limited | Real estate | 2012 |
| Packstat Limited | Wholesale & retail | 1990 |
| Pact for Autism | Information & communication | 2012 |
| Padel Kingdom (Colchester) Ltd | Arts & recreation | 2025 |
| Paediatric.Medical Limited | Health & social care | 2015 |
| Paes Property Investment Limited | Real estate | 2024 |
| Paes Services Limited | Real estate | 2020 |
| Page & Co Property Limited | Real estate | 2023 |
| Page Logistics Ltd | Transport & logistics | 2022 |
| Pague Ltd | Information & communication | 2025 |
| Painting the Past UK Limited | Financial services | 2024 |
| Pakand Construction Limited | Construction | 2019 |
| Pakege Limited | Transport & logistics | 2019 |
| Paklock 9 Limited | Hospitality | 2022 |
| PAL Interiors Ltd | Construction | 2024 |
| Palanquin Limited | Manufacturing | 2003 |
| Palazio Lifestyle Ltd | Transport & logistics | 2022 |
| Palbit Ltd | Construction | 2024 |
| Palm Beach Beauty Ltd | Wholesale & retail | 2025 |
| Palm Beach Studios Ltd | Other services | 2025 |
| Palmerston Road Residents (Buckhurst Hill) Limited | Real estate | 1973 |
| Palmerston Road Residents (Freehold) Limited | Real estate | 2000 |