| ORL Metals Ltd | Water & waste | 2015 |
| Orlapet Nutrition Ltd | Professional & scientific | 2021 |
| ORM Composites Ltd | Manufacturing | 2026 |
| Ormonde Holdings Ltd | Real estate | 2025 |
| Ornamental Plastics Co. Ltd | Extraterritorial | 2024 |
| Orphan Dame Limited | Other services | 2012 |
| Orsiva Limited | Information & communication | 2026 |
| Osaka Properties Limited | Real estate | 2016 |
| Osaka Toyota Specialists Limited | Wholesale & retail | 2009 |
| Osborne Height (Management Company) Limited | Households | 2002 |
| Oscar Electrical Services Ltd | Construction | 2026 |
| Osel Enterprises Limited | Other services | 1988 |
| Oseous Ltd | Information & communication | 2021 |
| OSG Property Renovations Ltd | Construction | 2018 |
| OSG Serviced Lets Ltd | Hospitality | 2018 |
| Osianhair Ltd | Other services | 2025 |
| Osman Smart Limited | Professional & scientific | 2014 |
| Osprey Stores Ltd | Wholesale & retail | 2019 |
| OSR Commercial Services Limited | Professional & scientific | 2014 |
| OSR Property Investments Ltd | Real estate | 2018 |
| OSS (UK) Limited | Wholesale & retail | 2002 |
| Osteon Medtech Ltd | Information & communication | 2025 |
| OT Nails Ltd | Other services | 2021 |
| Other World Terrariums Ltd | Wholesale & retail | 2023 |
| Otium Concierge Limited | Administrative & support | 2018 |
| Otium on Demand Limited | Public administration | 2024 |
| OTO Property Development Limited | Real estate | 2021 |
| OTS Developments Limited | Construction | 2024 |
| Otterburn Partners Limited | Information & communication | 2016 |
| Ottimo Digital Ltd | Manufacturing | 2009 |
| Ottley Properties IW Ltd | Real estate | 2026 |
| OUR New Home Limited | Real estate | 2018 |
| OUR Rivers (Cumbria) Ltd | Construction | 2025 |
| OUR Rivers (Norfolk) Ltd | Construction | 2024 |
| OUR Rivers Group Ltd | Professional & scientific | 2021 |
| OUR Voice Network Rhwydwaith EIN Llais CIC | Arts & recreation | 2024 |
| OUT of EAR Ltd | Health & social care | 2025 |
| Outbrake Ltd | Information & communication | 2023 |
| Outlet Apparel Ltd | Wholesale & retail | 2023 |
| Outlet Fashions Ltd | Wholesale & retail | 2017 |
| Outplan Finance Limited | Financial services | 2026 |
| Outsect Industries Limited | Manufacturing | 2015 |
| Outsourceuk Ltd | Professional & scientific | 2025 |
| Ovec Property Holdings Ltd | Real estate | 2022 |
| Over & Over Limited | Administrative & support | 2013 |
| Overwatch Holdings Ltd | Financial services | 2026 |
| Ovka Ltd | Real estate | 2024 |
| Owain Kelly Consulting Ltd | Administrative & support | 2014 |
| Oxford Sports and Fitness Ltd | Other services | 2016 |
| Oxford Street Fashion Limited | Wholesale & retail | 2026 |
| Oz-Meda Ltd | Real estate | 2020 |
| Ozcan Ergin Ltd | Manufacturing | 2019 |
| Ozion Properties Ltd | Real estate | 2025 |
| Ozzys Sports Bar Limited | Hospitality | 2017 |
| O’Whites Ltd | Real estate | 2023 |
| P & a Rann Construction Limited | Construction | 2017 |
| P & L Jackson Limited | Professional & scientific | 2011 |
| P & N Healthcare Services Ltd | Real estate | 2017 |
| P & P Dale Limited | Construction | 2003 |
| P & R Springs (Redditch) Limited | Manufacturing | 1988 |
| P & S Developments (Midlands) Limited | Construction | 1996 |
| P & V Property Developers Ltd | Real estate | 2026 |
| P Abbott Limited | Information & communication | 2021 |
| P B Cars 1988 Limited | Wholesale & retail | 2005 |
| P Becmer Ltd | Transport & logistics | 2024 |
| P C H Consultancy Limited | Professional & scientific | 2019 |
| P D ASH Plant Hire Limited | Construction | 2004 |
| P D M Produce (U.K.) Limited | Agriculture & fishing | 1996 |
| P Gane Limited | Construction | 2016 |
| P Gane Structures Ltd | Construction | 2025 |
| P Lane Building Services Ltd | Construction | 2022 |
| P M Colour Repro | | 1994 |
| P Morgan Driver Hire Limited | Transport & logistics | 2015 |
| P T Management Consultants Ltd | Professional & scientific | 2021 |
| P&H Rail Ltd | Construction | 2019 |
| P&M African Home & Fades Ltd | Wholesale & retail | 2026 |
| P&S Developments IOW Ltd | Real estate | 2025 |
| P. Farmer & SON Limited | Transport & logistics | 2003 |
| P.A. Scaffolding Hire Limited | | 1993 |
| P.B.S. (South Wales) Limited | Construction | 2002 |
| P.C. Cymru Care Limited | Administrative & support | 2007 |
| P.E. Composites Limited | Manufacturing | 2003 |
| P.E.C. Properties Limited | Real estate | 2013 |
| P.E.H. Property Developments Limited | Construction | 2003 |
| P.J. Pool Services Ltd | Other services | 2011 |
| P.J.C. Glazing (IOW) Limited | Construction | 2021 |
| P.L.A-Y! Active Community Interest Company | Education | 2021 |
| P.N.W Ltd | Construction | 2016 |
| P.S.R. Civils Group Limited | Construction | 2016 |
| P.S.R. Property Developments Limited | Financial services | 2025 |
| P7D Construct Ltd | Construction | 2021 |
| PA Inspection Limited | Professional & scientific | 2015 |
| Paat Limited | Other services | 2017 |
| Pace Forensic Solutions Limited | Professional & scientific | 2011 |
| Packhouse Properties Limited | Real estate | 1948 |
| Packpoint Logistics Limited | Transport & logistics | 2025 |
| PAD Managr Ltd | Real estate | 2025 |
| Padel & Performance Limited | Arts & recreation | 2026 |
| Padel Social Hub Limited | Arts & recreation | 2026 |
| Page Property Finance Ltd | Financial services | 2023 |