| Orange Lifting Solutions Ltd | Administrative & support | 2024 |
| Orangepxl Limited | Information & communication | 2023 |
| Orapal Limited | Information & communication | 2012 |
| Oravk Ltd | Wholesale & retail | 2025 |
| Orchardsview Ltd | Health & social care | 2020 |
| Orchestrate Limited | Manufacturing | 1993 |
| Orchid Medics Limited | Health & social care | 2021 |
| Ordalinc Services Limited | Administrative & support | 2016 |
| Orddel Limited | Information & communication | 2020 |
| Order First Limited | Financial services | 2018 |
| Order Xpress Ltd | Transport & logistics | 2023 |
| ORE Trade UK Ltd | Wholesale & retail | 2026 |
| Ore's Cakes Limited | Wholesale & retail | 2025 |
| Orenda Decor Limited | Construction | 2018 |
| Organic Dust Club Cleaning Ltd | Administrative & support | 2025 |
| Organic Spice Ltd | Hospitality | 2026 |
| Organics House Ltd | Wholesale & retail | 2020 |
| Orient 1 Construction Ltd | Construction | 2024 |
| Orient Capital Investments Limited | Real estate | 2022 |
| Oriental Care UK Limited | Health & social care | 2012 |
| Orientar Limited | Education | 2022 |
| Origin Infotech Limited | Information & communication | 2015 |
| Original Clean Limited | Administrative & support | 2024 |
| Original Cloves Limited | Hospitality | 2025 |
| Origins Living Limited | Wholesale & retail | 1994 |
| Orion Building Maintenance Ltd | Construction | 2014 |
| Orions Game Studio Ltd | Information & communication | 2025 |
| Oris Drycleaners (UK) Limited | Other services | 2007 |
| Orkit Ltd | Real estate | 2023 |
| Orophile Limited | Wholesale & retail | 2023 |
| Orphea Limited | Financial services | 2016 |
| Orsini Enterprises Limited | Arts & recreation | 2024 |
| Orthopaedia Surgery Limited | Health & social care | 2013 |
| Orudko Cladding Services Ltd | Construction | 2021 |
| Oryx IT Limited | Information & communication | 2024 |
| Oryxstore Ltd | Wholesale & retail | 2025 |
| OS JOI & Car Ltd | Construction | 2023 |
| Osana Corporation Limited | Real estate | 2024 |
| Osborne Heating Limited | Construction | 2013 |
| Osborne House Investment Ltd | Extraterritorial | 2017 |
| OSE Aesthetics Limited | Health & social care | 2026 |
| Oshodi Global Foods Ltd | Wholesale & retail | 2021 |
| Oshodi Property Group Ltd | Real estate | 2024 |
| Oski Studio Ltd | Arts & recreation | 2023 |
| Osman Foods Limited | Manufacturing | 2025 |
| Osprey Healthcare Academy UK Limited | Public administration | 2023 |
| Ossystar Ltd | Construction | 2021 |
| Osterley Park Limited | Real estate | 2011 |
| Ostraca Technologies Limited | Information & communication | 2012 |
| OT Media Group Ltd | Information & communication | 2019 |
| OTG Investments Limited | Real estate | 2023 |
| Ottomans Romford Ltd | Hospitality | 2025 |
| Otts Integrated Business Solutions Limited | Other services | 2020 |
| Oudfinity Ltd | Wholesale & retail | 2022 |
| Oughton Properties Limited | Real estate | 2019 |
| OUR Boys! Limited | Extraterritorial | 2009 |
| OUR Corner Stone Ltd | Health & social care | 2013 |
| OUT of Hours Ltd | Information & communication | 2020 |
| Outcast Management Limited | Professional & scientific | 2019 |
| Outlet Auto Ltd | Wholesale & retail | 2026 |
| Outlook Consultancy Services Limited | Professional & scientific | 2021 |
| Outpost Pictures Ltd | Information & communication | 2015 |
| Output-Sensitive Ltd | Information & communication | 2010 |
| Outright Accounting Ltd | Professional & scientific | 2017 |
| Outwearx Ltd | Wholesale & retail | 2025 |
| Ovenly Limited | Hospitality | 2017 |
| Overall Plumbing Limited | Construction | 2015 |
| Overblow Limited | Financial services | 2022 |
| Overleafdesign Limited | Professional & scientific | 2022 |
| Oversky Ltd | Construction | 2023 |
| Overstock Ltd | Water & waste | 2026 |
| Overt Media Ltd | Professional & scientific | 2023 |
| OVI Construction Ltd | Construction | 2020 |
| OVR Staffing Ltd | Administrative & support | 2023 |
| Ovuike Healthcare Ltd | Health & social care | 2005 |
| OVY Cons Limited | Construction | 2026 |
| Owomimo Limited | Manufacturing | 2023 |
| Oxatan Ltd | Construction | 2019 |
| Oxcart Trading Limited | Wholesale & retail | 2023 |
| Oxford FGC Ltd | Construction | 2024 |
| Oxwell (UK) Ltd | Other services | 2025 |
| OYE Creations Limited | Wholesale & retail | 2019 |
| OZ Estates London Ltd | Real estate | 2021 |
| Ozcomm Solutions Ltd | Information & communication | 2017 |
| Ozko Limited | Wholesale & retail | 2021 |
| Ozlee Homes Limited | Real estate | 2021 |
| Ozone (Weee) Recycling Limited | Administrative & support | 2012 |
| O’Loughlin (Camberwell) Limited | Real estate | 2016 |
| O’Toole Estate Management Ltd | Real estate | 2024 |
| P & a Construction Co. Ltd | Construction | 2010 |
| P & MBJ Limited | Extraterritorial | 2007 |
| P & V Data Cabling Ltd | Information & communication | 2021 |
| P D & J Ltd | Transport & logistics | 2022 |
| P D K Services Limited | Transport & logistics | 2018 |
| P Engineering Ltd | Energy | 2017 |
| P G S International Limited | Administrative & support | 2006 |
| P J Blanche M&E Services Ltd | Construction | 2019 |
| P J Drylining & Construction Limited | Construction | 2019 |
| P L Teller Ltd | Professional & scientific | 2016 |
| P M Danny Building Ltd | Construction | 2022 |