| Orange Transfers Ltd | Transport & logistics | 2023 |
| Orbital Building Control Limited | Professional & scientific | 2025 |
| Orchard Capital Allowances Limited | Professional & scientific | 2023 |
| Orchard Civils Ltd | Administrative & support | 2015 |
| Orchard Counselling Training Limited | Extraterritorial | 2026 |
| Orchard Heights Property Management Limited | Households | 2026 |
| Orchard House Leacroft Management Company Limited | Real estate | 2006 |
| Orchard Lane Kennington Limited | Real estate | 2015 |
| Orchard Life Limited | Wholesale & retail | 2026 |
| Orchard Pods Limited | Hospitality | 2017 |
| Orchidstream Limited | Extraterritorial | 2000 |
| Orel Private Limited | Wholesale & retail | 2026 |
| ORF Limited | Extraterritorial | 1984 |
| Orfea Conseil Ltd | Wholesale & retail | 2025 |
| Organic Grape Spirit Ltd | Manufacturing | 2019 |
| Oriental London Ltd | Hospitality | 2025 |
| Oriental Spanish Growers Ltd | Wholesale & retail | 2016 |
| Orion Accountancy Services Limited | Professional & scientific | 2018 |
| Orion Triple Three Ltd | Administrative & support | 2018 |
| Orlalee Grace CIC | Education | 2025 |
| Orlestone Data Services Limited | Information & communication | 2013 |
| Orlestone Enterprises Ltd | Other services | 2013 |
| Orlestoneoak Limited | Manufacturing | 1998 |
| Ormiston Renovations Ltd | Construction | 2023 |
| Orva Electrical Limited | Construction | 2025 |
| Osaro Intl Sports Academy Ltd | Arts & recreation | 2024 |
| Osben Ltd | Health & social care | 2025 |
| Osborne Stays Ltd | Hospitality | 2024 |
| Osbourn White Ltd | Professional & scientific | 2011 |
| Osbourne Court Faversham Limited | Construction | 2025 |
| Oscar's DEN (London) Ltd | Wholesale & retail | 1965 |
| Oscare Services Limited | Education | 2017 |
| OSG Architecture Limited | Professional & scientific | 2013 |
| Oshcomm Ltd | Information & communication | 2023 |
| Oshn Limited | Education | 2005 |
| Osos Construction Ltd | Construction | 2020 |
| Osos Modular Ltd | Construction | 2020 |
| Osprey Electrical and AV Ltd | Construction | 2022 |
| OSS Partners Ltd | Professional & scientific | 2023 |
| OTC Concepts Limited | Manufacturing | 2002 |
| OTC Management Consultancy Ltd | Construction | 2026 |
| Other Dimension Films Limited | Professional & scientific | 2011 |
| Otisan Limited | Administrative & support | 2016 |
| Otium Farm Ltd | Agriculture & fishing | 2026 |
| Otom Consulting Ltd | Information & communication | 2023 |
| Oton Properties Ltd | Real estate | 2021 |
| OTR Productions Limited | Information & communication | 2022 |
| OTS Cabs Ltd | Wholesale & retail | 2026 |
| Otten Limited | Information & communication | 2014 |
| Ottewill Silversmiths & Jewellers Ltd | Wholesale & retail | 2011 |
| Ottie Design Ltd | Professional & scientific | 2023 |
| Otto Squad Ltd | Real estate | 2018 |
| OTY Oak Frames Limited | Construction | 2020 |
| OTY Oak Homes Limited | Construction | 2018 |
| Ounje OLA Limited | Manufacturing | 2025 |
| OUR Kids Foundation | Health & social care | 2009 |
| OUR Place WYE CIC | Health & social care | 2016 |
| OUT of Home Experts Limited | Extraterritorial | 2021 |
| OUT of OUR Tree Ltd | Education | 2014 |
| OUT of the Woods Therapies Ltd | Health & social care | 2023 |
| Outcaste Music Publishing Limited | Information & communication | 2001 |
| Outcaste Records Limited | Information & communication | 1995 |
| Outdoor Cooking Company Limited | Hospitality | 2023 |
| Outdoor Experts Limited | Extraterritorial | 2021 |
| Outens Detailing Ltd | Wholesale & retail | 2025 |
| Outline Construction South East Limited | Construction | 2025 |
| Outstanding Inside Ltd | Health & social care | 2026 |
| Outworkme Ltd | Wholesale & retail | 2024 |
| Oven Wizards (Kent) Limited | Administrative & support | 2010 |
| Ovenda Limited | Wholesale & retail | 2019 |
| Ovenden Flooring Limited | Construction | 2023 |
| Ovengleam Cleaning Company Limited | Other services | 2004 |
| Overall Enterprises Limited | Construction | 2010 |
| Ow-Six Limited | Real estate | 2024 |
| Ownterm Property Management Limited | Households | 1995 |
| Oxfordwell Property Co Ltd | Real estate | 2021 |
| Oxney PUB Group Limited | Hospitality | 2007 |
| Oxygen Life Sciences Ltd | Professional & scientific | 2019 |
| P & J Breen Limited | Transport & logistics | 2016 |
| P & M Electrical Wholesale Ltd | Wholesale & retail | 1999 |
| P & R Home Improvements Ltd | Construction | 2020 |
| P & R Investments (Kent) Limited | Construction | 2013 |
| P & Z Domos Ltd | Health & social care | 2022 |
| P a Properties (Folkestone) Limited | Real estate | 2025 |
| P Burr Limited | Construction | 2021 |
| P Gadsden Groundworks Limited | Construction | 2020 |
| P J Building Construction Ltd | Construction | 2004 |
| P J Cole (Southern) Holdings Limited | Professional & scientific | 2015 |
| P J Construction Company (London) Limited | Real estate | 1989 |
| P J Hourigan Brickwork Ltd | Construction | 2007 |
| P K Saunders Electrical Ltd | Construction | 2022 |
| P M Assheton Ltd | Construction | 2015 |
| P M Viney and SON Ltd | Wholesale & retail | 2024 |
| P Marian Ltd | Transport & logistics | 2017 |
| P S Murphy Cleaning Services Ltd | Administrative & support | 2006 |
| P Worsley Contractors Ltd | Construction | 2026 |
| P&D Aston Consultancy Limited | Professional & scientific | 2023 |
| P&O European Ferries (Irish Sea) Limited | Transport & logistics | 1936 |
| P&O European Ferries (Portsmouth) Limited | Transport & logistics | 1964 |
| P&O Ferries (Short Sea) Limited | Transport & logistics | 1996 |