| One Avenue Managed Limited | Real estate | 2013 |
| One Avenue Managed Offices Limited | Real estate | 2022 |
| One Avenue Management Services Limited | Real estate | 2021 |
| One Avenue Mayfair Limited | Real estate | 2020 |
| One Avenue Park Lane Limited | Real estate | 2021 |
| One Avenue Petty France Management Limited | Real estate | 2015 |
| One Avenue Property Holdings Limited | Financial services | 2023 |
| One Avenue Serviced Office Division Limited | Real estate | 2013 |
| One Avenue Southwark Street Limited | Real estate | 2018 |
| One Avenue ST Johns Lane Limited | Real estate | 2021 |
| One Avenue Trading Limited | Professional & scientific | 2020 |
| One Ball Buggies Ltd | Wholesale & retail | 2024 |
| One Dovercourt LLP | | 2024 |
| One Learning Journey Limited | Education | 2011 |
| One New Fosseway LLP | | 2024 |
| One Price Fabric Ltd | Wholesale & retail | 2013 |
| One Touch Electrical Ltd | Construction | 2019 |
| One Window Solutions Ltd | Information & communication | 2018 |
| One Winning Product Ltd | Wholesale & retail | 2021 |
| ONE12TEN Ltd | Information & communication | 2026 |
| Oneiros Designs Limited | Professional & scientific | 2017 |
| Oneteam Motors Limited | Wholesale & retail | 2020 |
| Ongar 27 Kebab Limited | Hospitality | 2026 |
| Ongar 27 Ltd | Hospitality | 2024 |
| Ongar Carpenters Limited | Extraterritorial | 2013 |
| Ongar News Community Interest Company | Information & communication | 2014 |
| Ongar RD Mini Market Ltd | Wholesale & retail | 2024 |
| Ongar Road Kebab Ltd | Hospitality | 2020 |
| Ongar Road Kitchen Ltd | Hospitality | 2024 |
| Ongar Road Property Management Limited | Real estate | 2015 |
| Onijoko Limited | Health & social care | 2022 |
| Onit Properties Limited | Real estate | 2026 |
| Onsite Suppliers Ltd | Construction | 2026 |
| Onslow Developments Limited | Construction | 2017 |
| Onthemoov Ltd | Information & communication | 2020 |
| Onwards and Upwards Management Ltd | Real estate | 2018 |
| Onyer Marx UK Ltd | Professional & scientific | 2018 |
| Onyst Ltd | Wholesale & retail | 2024 |
| Onyx Brokers Holdings Limited | Financial services | 2019 |
| Onyx INS Company Limited | Financial services | 2019 |
| Onyx Plumbing Ltd | Construction | 2009 |
| OOB Scaffolding Limited | Construction | 2009 |
| Ootvgooner Ltd | Information & communication | 2024 |
| Ooznest Holdings Limited | Financial services | 2021 |
| Ooznest Limited | Wholesale & retail | 2015 |
| Opal Consultancy Ltd | Professional & scientific | 2023 |
| Opal Global Holdings Ltd | Financial services | 2026 |
| Open Door Accountancy Ltd | Professional & scientific | 2026 |
| Open Innovations Ventures Limited | Professional & scientific | 2025 |
| Open Key Homes Ltd | Real estate | 2021 |
| OPENC247.COM Limited | Information & communication | 2020 |
| Opheus Managing Agencies Limited | Financial services | 2019 |
| OPM Global Group Ltd | Construction | 2023 |
| Opportunities Workshop Limited | Professional & scientific | 2012 |
| Optical.Network.Engineering Ltd | Construction | 2020 |
| Optimising Health Limited | Education | 2022 |
| Optimum Control Solutions Limited | Professional & scientific | 2020 |
| Optimum System Balancing Ltd | Professional & scientific | 2017 |
| Optimum Tree Services Ltd | Agriculture & fishing | 2019 |
| Optom Properties Limited | Real estate | 2023 |
| Optom-Tech Solutions Ltd | Information & communication | 2015 |
| Opus Financial Services Limited | Financial services | 2015 |
| Oral Hygiene Centre Ltd | Health & social care | 2007 |
| Orange Clothing Company Limited | Wholesale & retail | 1993 |
| Orbit Consulting Limited | Health & social care | 2005 |
| Organic Beauty (UK) Ltd | Wholesale & retail | 2009 |
| Organic Food Stock Ltd | Professional & scientific | 2022 |
| Organicer Ltd | Information & communication | 2026 |
| Oribelle Consulting Ltd | Information & communication | 2015 |
| Oribelle Limited | Information & communication | 2025 |
| Orion GUN Club Limited | Arts & recreation | 2004 |
| Orion Investments & Management Limited | Health & social care | 2002 |
| Orion Investments Limited | Financial services | 2022 |
| OS (2024) Limited | Information & communication | 2019 |
| Osborn Transport Limited | Transport & logistics | 2022 |
| Osborne Property Investment Limited | Real estate | 2010 |
| OSJ Real Estate Ltd | Real estate | 2013 |
| Osper Ltd | Information & communication | 2012 |
| Otaina Limited | Information & communication | 2023 |
| OTS Mechanical Services Limited | Construction | 2022 |
| OUR Healthcare Hub Ltd | Professional & scientific | 2025 |
| Outings Lane Ltd | Real estate | 2015 |
| Outings Lane Management Company Limited | Real estate | 2017 |
| Outworlder Ltd | Wholesale & retail | 2022 |
| Oveli Limited | Financial services | 2024 |
| Overplan Services Limited | Construction | 1999 |
| Overton View LLP | | 2023 |
| Owango Renaissance Ltd | Professional & scientific | 2008 |
| Own True Path Ltd | Professional & scientific | 2020 |
| Oxenton Consultancy Ltd | Professional & scientific | 2025 |
| Oxford Dentist Limited | Health & social care | 2015 |
| Oxfordshire Commercials Ltd | Construction | 2023 |
| OXO Presta Ltd | Professional & scientific | 2023 |
| Oyster Shack and Seafood Bar Ltd | Hospitality | 2020 |
| Ozark Investment Ltd | Wholesale & retail | 2019 |
| Ozmo INT Ltd | Wholesale & retail | 2017 |
| P & a Heritage Ltd | Real estate | 2022 |
| P & H General Engineering Ltd | Professional & scientific | 2009 |
| P & J Moore Limited | Professional & scientific | 2019 |
| P & M Inventories Limited | Real estate | 2011 |