| OM Developments (London) Limited | Construction | 2007 |
| OM Grocery Limited | Wholesale & retail | 2024 |
| OM VEG Ltd | Wholesale & retail | 2017 |
| Omamia Limited | Transport & logistics | 2018 |
| Omega Brides and Sarees Limited | Manufacturing | 2017 |
| OMJ Cars Ltd | Transport & logistics | 2022 |
| Omnarais Ltd | Information & communication | 2026 |
| Omnisencepharma Ltd | Health & social care | 2023 |
| ON Time UK Services Ltd | Transport & logistics | 2026 |
| Once a Lost Sheep Ltd | Arts & recreation | 2024 |
| One Best Deal Ltd | Wholesale & retail | 2022 |
| One Link Distributions Online Ltd | Wholesale & retail | 2015 |
| One Piece NAZ Ltd | Manufacturing | 2026 |
| One Pound Mart Ltd | Wholesale & retail | 2026 |
| One Stop Local Ltd | Wholesale & retail | 2025 |
| One Stop Packaging Solution Limited | Wholesale & retail | 2026 |
| One Stop Shop Wholesale Limited | Wholesale & retail | 2022 |
| Oneb Cosmetics Ltd | Wholesale & retail | 2023 |
| Onebrand Limited | Wholesale & retail | 2019 |
| Onerealestate Ltd | Real estate | 2021 |
| Onkar International Limited | Construction | 1980 |
| Onkar Singh Ltd | Construction | 2022 |
| Online CPD Training Ltd | Education | 2026 |
| Online Zone Ltd | Wholesale & retail | 2019 |
| Onroad Transfers Ltd | Hospitality | 2017 |
| Onyx-Algo Ltd | Information & communication | 2026 |
| Opalmex Limited | Real estate | 2006 |
| Opalsky Journeys Limited | Wholesale & retail | 2025 |
| OPC Mobile Car Valeting Ltd | Administrative & support | 2024 |
| Openest Ltd | Hospitality | 2025 |
| Opinion Designer Wear Ltd | Wholesale & retail | 2024 |
| Opportunity & Co. Property Group Ltd | Real estate | 2025 |
| Opthalmic Medical Services Limited | Health & social care | 1997 |
| Optical World (Southall) Ltd | Health & social care | 2011 |
| Optimise Ltd | Information & communication | 2025 |
| Optiprime Solutions Ltd | Health & social care | 2024 |
| Optoverse Ltd | Wholesale & retail | 2026 |
| OPY Construction Ltd | Construction | 2020 |
| Opy&Rs Ltd | Construction | 2019 |
| ORA Digital Ltd | Wholesale & retail | 2026 |
| Oracle Capital Ltd | Professional & scientific | 2021 |
| Oracle Pmsh Ltd | Wholesale & retail | 2023 |
| Orans London Limited | Wholesale & retail | 2025 |
| Orbiquex Technologies UK Limited | Information & communication | 2024 |
| Orbis Travels Ltd | Other services | 2011 |
| Orchard Wholesale Limited | Wholesale & retail | 2004 |
| Orchard Wirral Property Ltd | Real estate | 2026 |
| Orchard Wirral Surgery Ltd | Health & social care | 2026 |
| Organa Technology Ltd | Manufacturing | 2023 |
| Organised Rhyme Limited | Information & communication | 1999 |
| Origin Custom Homes Construction Ltd | Construction | 2019 |
| Origin Custom Homes Ltd | Professional & scientific | 2013 |
| Origin Textiles Ltd | Wholesale & retail | 2024 |
| Original Edge Ltd | Wholesale & retail | 2013 |
| Originsales Ltd | Wholesale & retail | 2020 |
| Oringo Cart Ltd | Wholesale & retail | 2025 |
| Orion Holdings Group Ltd | Real estate | 2026 |
| Orson Services Limited | Transport & logistics | 2025 |
| Oryon Security Services Ltd | Administrative & support | 2025 |
| Osciebella Ltd | Information & communication | 2021 |
| OSI Connect Ltd | Wholesale & retail | 2017 |
| Osiris Productions Ltd | Construction | 2021 |
| Osreuk Ltd | Real estate | 2020 |
| OSREUKR2B Ltd | Financial services | 2025 |
| Ossan Motors Ltd | Wholesale & retail | 2025 |
| Ossi Ltd | Other services | 2017 |
| Osterley Food and Wine Ltd | Wholesale & retail | 2023 |
| Oswal Ltd | Construction | 2026 |
| Otaiy Limited | Wholesale & retail | 2024 |
| Ottomotive Ltd | Wholesale & retail | 2024 |
| OUD Palace Limited | Manufacturing | 2022 |
| OUR Barber Limited | Other services | 2024 |
| OUR Moving Stories CIC | Arts & recreation | 2022 |
| OUR Quarters Ltd | Real estate | 2023 |
| OUR Smile Ltd | Real estate | 2020 |
| Outbond Limited | Wholesale & retail | 2018 |
| Outkast Consultants Limited | Administrative & support | 2019 |
| Overseas Immigration Services UK Ltd. | Other services | 2012 |
| Overseas Pakistan Lovers Limited | Extraterritorial | 2016 |
| Ovrtheline Ltd | Professional & scientific | 2026 |
| Owrhr Ventures Limited | Manufacturing | 2025 |
| Oxford Green Energy Limited | Professional & scientific | 2020 |
| Oxfordshire Nanoc Ltd | Financial services | 2024 |
| OXO Fabrics Ltd | Wholesale & retail | 2025 |
| Ozzy Building Services Ltd | Construction | 2021 |
| P & J Retail Limited | Wholesale & retail | 2023 |
| P & K Transport Services Ltd | Transport & logistics | 2026 |
| P & S Partners Ltd | Real estate | 2023 |
| P B Autos Limited | Wholesale & retail | 2018 |
| P H (Slough) Ltd | Construction | 2014 |
| P Mayer Ltd | Construction | 2021 |
| P S G Courier & Removals Ltd | Construction | 2020 |
| P S Gill Roofing Ltd | Construction | 2021 |
| P&G Investments London Ltd | Real estate | 2024 |
| P&G London Limited | Wholesale & retail | 2025 |
| P&R (Impex) Limited | Transport & logistics | 2022 |
| P.R.S. Southall Limited | Wholesale & retail | 2011 |
| P.S.S.G Logistics Ltd | Transport & logistics | 2015 |
| P9 Ltd | Construction | 2026 |
| Packaging Distribution Limited | Wholesale & retail | 2025 |