| Onlylove Eyewear Co., Limited | Wholesale & retail | 2023 |
| Onthemap Deliveries Ltd | Transport & logistics | 2020 |
| Ontime Global Logistics Ltd | Extraterritorial | 2016 |
| Ontime Supply Chain Co., Ltd | Wholesale & retail | 2021 |
| Ooxs Lubricants Company Limited | Extraterritorial | 2015 |
| Opal Abode Ltd | Real estate | 2026 |
| Openfish Ltd | Wholesale & retail | 2021 |
| Opportunit Limited | Information & communication | 1997 |
| Opsclarity Limited | Professional & scientific | 2025 |
| Optimus Device Company Limited | Manufacturing | 2022 |
| Optisource (Tianjin) International Trade Co., Ltd | Extraterritorial | 2017 |
| Opulentskin Brands UK Ltd | Extraterritorial | 2025 |
| Orange and Black Ltd | Hospitality | 2022 |
| Orange Leaf Consulting Ltd | Information & communication | 2022 |
| Orastock Ltd | Health & social care | 2018 |
| Orbityre Group Co., Limited | Extraterritorial | 2014 |
| Orchard Court the Knoll Limited | Households | 2018 |
| Orches Limited | Extraterritorial | 2020 |
| Orelaja Properties Limited | Real estate | 2023 |
| Organic Club Group Limited | Extraterritorial | 2018 |
| Organising Claudia Ltd | Administrative & support | 2022 |
| Oriana Court (Croydon) Management Company Limited | Households | 2003 |
| Oriana Court RTM Company Limited | Households | 2021 |
| Orien Group Co., Ltd. | Extraterritorial | 2018 |
| Orient Estrellas Trade Co., Ltd | Extraterritorial | 2020 |
| Orient Industrial Co., Ltd | Extraterritorial | 2013 |
| Orient Willing Technical Development Co., Limited | Extraterritorial | 2018 |
| Oriental Evergreen Group Company Ltd | Extraterritorial | 2015 |
| Oriental Shipping Service Limited | Manufacturing | 2024 |
| Oriental Superstar Limited | Wholesale & retail | 2021 |
| Orientech Electronics Co., Ltd | Professional & scientific | 2013 |
| Origin Group Property Limited | Households | 2022 |
| Origin Projects Limited | Professional & scientific | 2004 |
| Original Management Limited | Extraterritorial | 2006 |
| Original Zone Limited | Professional & scientific | 2018 |
| Orlando Gray Management Ltd | Arts & recreation | 2015 |
| Oroko Design Limited | Professional & scientific | 2016 |
| ORS Studio Limited | Construction | 2025 |
| Orsen Technology Co., Ltd. | Extraterritorial | 2018 |
| Ortus Engineering Ltd | Manufacturing | 2015 |
| OS Holding Group Limited | Extraterritorial | 2018 |
| Osac Ltd | Information & communication | 2015 |
| Oscar AMI Ltd | Financial services | 2023 |
| Oshengyi Co., Ltd | Wholesale & retail | 2024 |
| Osion Group Limited | Wholesale & retail | 2022 |
| Osmunda Medical Technology Limited | Other services | 2021 |
| OTA Enterprises Limited | Professional & scientific | 2004 |
| Othman Import and Export Company Limited | Wholesale & retail | 2023 |
| Otium QUO Limited | Hospitality | 2014 |
| OTJ Delivery Ltd | Hospitality | 2021 |
| Otstec Elevator Co., Ltd. | Extraterritorial | 2015 |
| Otter Munro Limited | Professional & scientific | 2026 |
| Ottimo Supply Chain Corporation Ltd | Wholesale & retail | 2016 |
| Otto Solutions Limited | Professional & scientific | 2022 |
| Otway & Golder,Limited | Extraterritorial | 1928 |
| Ouchi Trading Limited | Manufacturing | 2019 |
| Ouhua Belgium Xingji Special Fertilizer International Trade Ltd | Extraterritorial | 2024 |
| Oupeike Co., Ltd | Extraterritorial | 2014 |
| OUR Health LAB Ltd | Health & social care | 2021 |
| OUR Project Time CIC | Education | 2026 |
| OUT of Africa Travel & Golf Limited | Administrative & support | 2005 |
| Outimer Co., Limited | Extraterritorial | 2014 |
| Outsourced ACC Limited | Real estate | 2014 |
| Outsourced Property Ltd | Real estate | 2018 |
| Over Exposure Events Ltd | Administrative & support | 2026 |
| Overbury (Bromley) Limited | Extraterritorial | 1995 |
| Overstep Industry Co. Limited | Extraterritorial | 2022 |
| Ovictor Group Co., Ltd | Manufacturing | 2023 |
| Owendale Management Limited | Households | 1984 |
| Owill Trading Electronics Ltd. | Manufacturing | 2025 |
| Owntake Property Management Limited | Households | 1998 |
| Ox-In-Flames Limited | Wholesale & retail | 2001 |
| Oxbridge Masterclasses Ltd | Education | 2015 |
| Oxta Design Limited | Professional & scientific | 2022 |
| Oyami Smart Home Europe Ltd | Extraterritorial | 2019 |
| Oyang International Co., Ltd | Manufacturing | 2024 |
| OZC Make UP Limited | Extraterritorial | 2022 |
| Ozzie's Barber Company Ltd | Other services | 2016 |
| P M Bennison Heating Ltd | Construction | 2012 |
| P R D Heating & Plumbing Ltd | Construction | 2020 |
| P&T Industry Co., Limited | Extraterritorial | 2019 |
| P. Griffin Developments & Properties Limited | Construction | 2015 |
| P. Griffin Developments Limited | Construction | 2009 |
| P. Griffin Houses Ltd | Real estate | 2025 |
| P.H.L. Properties Limited | Households | 2007 |
| P.K.S Co., Ltd | Extraterritorial | 2019 |
| P.L. Exports Co., Ltd. | Manufacturing | 2015 |
| P.W. Knowles Construction Limited | Construction | 2002 |
| P3 Data Compliance Solutions Limited | Professional & scientific | 2018 |
| Pacepal Ltd | Arts & recreation | 2024 |
| Pacsin Mechanical Equipment Co., Ltd | Extraterritorial | 2017 |
| Paediatric Hepatology Associates Limited | Health & social care | 2010 |
| PAI. Tech Limited | Manufacturing | 2022 |
| Paint and Body ARS Ltd | Wholesale & retail | 2011 |
| Palace Bathrooms Limited | Construction | 2022 |
| Palace Communications Limited | Information & communication | 1983 |
| Palace Property Group Ltd | Real estate | 2025 |
| Palace Road Management Company Limited | Households | 2004 |
| Palladian Medical Consulting Ltd | Health & social care | 2023 |
| Palls International Holding Corporation Ltd | Manufacturing | 2015 |