| Optimus Consulting Holdings Ltd | Real estate | 2020 |
| Optional Excursions Limited | Transport & logistics | 2018 |
| Options Investments Ltd | Real estate | 2013 |
| Options Mortgage Centre Limited | Financial services | 2022 |
| Optune Homes Limited | Construction | 2007 |
| Orana-Wurren Ltd | Education | 2026 |
| Orange Fish Limited | Hospitality | 2018 |
| Orange Mart Ltd | Wholesale & retail | 2025 |
| Orca Support Ltd | Wholesale & retail | 2021 |
| Orchard Ovens Limited | Manufacturing | 2013 |
| Orchestral Music Ltd | Information & communication | 2026 |
| Oria App Ltd | Information & communication | 2021 |
| Orient Dental Laboratory Ltd | Health & social care | 1997 |
| Origin Technology Limited | Information & communication | 2021 |
| Orion Blinds Limited | Manufacturing | 2002 |
| Orios Flooring Services Limited | Construction | 2003 |
| Orme Test Solutions Ltd | Information & communication | 2025 |
| Ornate Investment Managers Limited | Professional & scientific | 2024 |
| ORR Elite Properties Ltd | Real estate | 2026 |
| ORR Services Limited | Professional & scientific | 2010 |
| Orujlu Business Automation Services Ltd | Information & communication | 2023 |
| Orzelek Ltd | Wholesale & retail | 2017 |
| Osayi African Kitchen Limited | Hospitality | 2020 |
| OSB Property Ltd | Real estate | 2022 |
| Osborne Plumbing and GAS Ltd | Construction | 2017 |
| Osker Limited | Administrative & support | 2012 |
| Ostara Property Rentals Ltd | Hospitality | 2024 |
| OTC Property Ltd | Real estate | 2025 |
| Otech Systems Limited | Information & communication | 2016 |
| Ouiaa Worldwide Ltd | Other services | 2025 |
| OUR Little Bunny Company Limited | Wholesale & retail | 2023 |
| Ourvita UK Limited | Wholesale & retail | 2022 |
| Outbound Academy Limited | Education | 2018 |
| Outbound Care Limited | Health & social care | 2017 |
| Outcast Ventures Ltd | Information & communication | 2015 |
| Outreach Hospitality Limited | Hospitality | 2018 |
| Outsourced Artwork Limited | Administrative & support | 2010 |
| Over the World Imports Exports Ltd | Wholesale & retail | 2019 |
| Overlander Technologies Holdings Ltd | Financial services | 2019 |
| Overman Ltd | Information & communication | 2018 |
| Oversands View Management Company Limited | Households | 2015 |
| Overwyre Limited | Professional & scientific | 2012 |
| Owen (NDT) Inspection Services Limited | Mining & quarrying | 2014 |
| Owen Group Ltd | Real estate | 2015 |
| OWL Foods Ltd | Hospitality | 2023 |
| Owllegal Limited | Professional & scientific | 2014 |
| Oxford Builders (AL) Limited | Construction | 2013 |
| Oxford Readings Limited | Administrative & support | 2013 |
| Oxford ROW Management Company Ltd | Households | 2000 |
| Oxygym Health and Fitness Limited | Arts & recreation | 2007 |
| Oxygym Ltd | Arts & recreation | 2022 |
| Oyster and POP Limited | Wholesale & retail | 2020 |
| Oyster Publishing Ltd | Information & communication | 2023 |
| Oyster Yachting Ltd | Extraterritorial | 2023 |
| Ozara HR Ltd | Administrative & support | 2023 |
| Ozarpaci Ltd | Extraterritorial | 2023 |
| Ozon Marine Limited | Extraterritorial | 2023 |
| Ozone (NW) Ltd | Hospitality | 2019 |
| O’Connors Travel Limited | Administrative & support | 2025 |
| O’Neill’S Property Group Ltd | Households | 2025 |
| P & B PUB Company Ltd | Hospitality | 2007 |
| P & J Byford Holdings Ltd | Real estate | 2025 |
| P & J Hotels Limited | Hospitality | 2024 |
| P & L Stephenson Properties Limited | Real estate | 2020 |
| P & R Acquisitions Limited | Real estate | 2012 |
| P & W Auto Services Limited | Wholesale & retail | 2014 |
| P and P Electrical Services Limited | Construction | 1996 |
| P Bayliss Limited | Real estate | 1999 |
| P F & F (UK) Limited | Construction | 2011 |
| P Hannigan Plasterers Limited | Construction | 2003 |
| P L Civils Limited | Construction | 2009 |
| P L Fabrications Limited | Manufacturing | 2014 |
| P LAL Limited | Health & social care | 2013 |
| P&H Legacy Holdings Ltd | Financial services | 2025 |
| P&H Residential Letting Ltd | Real estate | 2025 |
| P&M Payne Properties Ltd | Real estate | 2021 |
| P&S Convenience Stores Limited | Wholesale & retail | 2021 |
| P.& B.L.Investments Limited | Real estate | 1941 |
| P.D.M. Props Ltd | Wholesale & retail | 2025 |
| P.K. Parties Ltd | Arts & recreation | 2012 |
| P.K.L.D. Limited | Construction | 2007 |
| P.P.Planning Limited | Professional & scientific | 2017 |
| P.T.J Housing Ltd | Real estate | 2020 |
| P1ANT Ltd | Administrative & support | 2011 |
| PA Hire Lancashire Ltd | Administrative & support | 2024 |
| Pablo Property Investment Ltd | Real estate | 2025 |
| Pace Design & Build Ltd Ltd | Construction | 2025 |
| Packetfabric (UK) Ltd | Information & communication | 2014 |
| Packsafe Products Ltd | Wholesale & retail | 2009 |
| Paddock Emet Ltd | Wholesale & retail | 2025 |
| Padelfrog Limited | Wholesale & retail | 2025 |
| Padmam Limited | Information & communication | 2018 |
| Paintcom Systems Limited | Information & communication | 2001 |
| Paka Limited | Other services | 2019 |
| Palco Holdings Ltd | Hospitality | 2020 |
| Palladian Healthcare Limited | Water & waste | 2015 |
| Palladium Energy Supply Limited | Energy | 2014 |
| Palmas Stays Ltd | Hospitality | 2023 |
| Pamar Developments Ltd | Wholesale & retail | 2025 |
| Pamela Nicholls Security Limited | Administrative & support | 2025 |