| Ostro Properties Limited | Real estate | 2024 |
| Ostuni Bakery Limited | Manufacturing | 2026 |
| Ostuni Limited | Hospitality | 2021 |
| Osztreicher Properties Limited | Extraterritorial | 2024 |
| Otakumise Ltd | Wholesale & retail | 2023 |
| Otanoshike Ltd | Wholesale & retail | 2020 |
| Otees Healthcare and Mangement Agency Limited | Health & social care | 2022 |
| Otenox Ltd | Wholesale & retail | 2025 |
| Oteob Ltd | Other services | 2023 |
| OTF Transport Limited | Transport & logistics | 2023 |
| Otgc Ltd | Professional & scientific | 2022 |
| Othala Ltd | Information & communication | 2024 |
| Otherworld DEV Ltd | Manufacturing | 2026 |
| Otid Entertainment Ltd | Professional & scientific | 2024 |
| Otif Distribution Limited | Transport & logistics | 2016 |
| Otis Bookkeeping Ltd | Professional & scientific | 2021 |
| Otis Property Solutions Ltd | Real estate | 2025 |
| Otis Raul Limited | Information & communication | 2021 |
| Otis Roberts Limited | Wholesale & retail | 2025 |
| Otium Solutions Worldwide Ltd | Professional & scientific | 2018 |
| Otium Works Ltd | Hospitality | 2020 |
| OTJ Developments Ltd | Real estate | 2025 |
| OTK Distribution Ltd | Transport & logistics | 2023 |
| Otleythames UK Limited | Transport & logistics | 2017 |
| OTM Plumbing and Heating Ltd | Construction | 2022 |
| Otrik Solutions Ltd | Administrative & support | 2020 |
| Ottalex Limited | Information & communication | 2012 |
| Otter Enterprises Limited | Manufacturing | 2021 |
| Otter Grove Limited | Construction | 2004 |
| Otto Consulting Ltd | Information & communication | 2016 |
| OU Rouge Limited | Manufacturing | 2017 |
| Ouaali Ltd | Wholesale & retail | 2025 |
| Ouadig Marketing Ltd | Wholesale & retail | 2024 |
| Oucham Agoro Limited | Wholesale & retail | 2025 |
| OUD Kayan Ltd | Wholesale & retail | 2025 |
| Oudxotica Ltd | Wholesale & retail | 2025 |
| OUI Translate Ltd | Professional & scientific | 2015 |
| Ouinich Limited | Wholesale & retail | 2023 |
| Oukjie International Holding Group (UK) Co., Limited | Extraterritorial | 2020 |
| OUR Flow Ltd | Water & waste | 2025 |
| OUR Future Sw&Uk Ltd | Administrative & support | 2025 |
| OUR Good Days Company Ltd | Wholesale & retail | 2018 |
| OUR Little Globe Ltd | Wholesale & retail | 2017 |
| OUR Locals England Ltd | Professional & scientific | 2020 |
| OUR Mynachdy Community | Health & social care | 2019 |
| OUR Own House Ltd | Administrative & support | 2015 |
| OUR Parently Ltd | Education | 2026 |
| OUR Rhythm Ltd | Arts & recreation | 2014 |
| OUR Space Worldwide Ltd | Arts & recreation | 2022 |
| OUR Visual World Ltd | Arts & recreation | 2025 |
| Ouranos Consulting Limited | Real estate | 2013 |
| Ourelitehealth PVT Limited | Wholesale & retail | 2025 |
| Ourown Designs Limited | Construction | 2017 |
| Ouroxhome | Professional & scientific | 2023 |
| Ours World Trading Company Limited | Transport & logistics | 2022 |
| Ouse Bridge House Ltd | Hospitality | 2010 |
| Oussarh Ltd | Wholesale & retail | 2025 |
| OUT for Millz Ltd | Wholesale & retail | 2020 |
| OUT of School Childcare Limited | Education | 2019 |
| OUT of This World Investments Ltd | Financial services | 2020 |
| OUT on the Town Limited | Wholesale & retail | 2020 |
| Outback Logic Limited | Wholesale & retail | 2015 |
| Outcomes Over Outputs Ltd | Information & communication | 2022 |
| Outdoor Fitness Ltd | Health & social care | 2008 |
| Outfront Solutions Ltd | Information & communication | 2025 |
| Outis Insure Ltd | Financial services | 2025 |
| Outlander Ltd | Wholesale & retail | 2025 |
| Outlarge Consults Limited | Professional & scientific | 2017 |
| Outlet Prices Direct Group Ltd | Wholesale & retail | 2021 |
| Outletlocker Ltd | Other services | 2025 |
| OUTLETMÖBEL24 Ltd | Information & communication | 2018 |
| Outloud Studios Ltd | Information & communication | 2025 |
| Outmail Ltd | Information & communication | 2025 |
| Outpost Cardiff Limited | Hospitality | 2022 |
| Outpost CDF Limited | Wholesale & retail | 2016 |
| Outpost Cloud Path Ltd | Information & communication | 2025 |
| Outright Collectables Limited | Wholesale & retail | 2018 |
| Outsource Bookkeeping & Payroll Ltd | Information & communication | 2013 |
| Outsource Strategies Ltd | Administrative & support | 2020 |
| Outsourced Trading Group Limited | Financial services | 2017 |
| Outspire Group Limited | Other services | 2012 |
| Outsprint Ltd | Information & communication | 2019 |
| Outstanding Ocean Ltd | Wholesale & retail | 2025 |
| Outstandish Ltd | Construction | 2023 |
| Outstream Laboratory Limited | Information & communication | 2014 |
| Ovadeooo Ltd | Construction | 2019 |
| Oval Financial Management Limited | Financial services | 2011 |
| Ovarish Limited | Wholesale & retail | 2025 |
| Ovarium Limited | Wholesale & retail | 2025 |
| OVE Solutions Ltd | Professional & scientific | 2022 |
| Ovenbright & Beyond Ltd | Administrative & support | 2025 |
| Oveno Solutions Ltd | Wholesale & retail | 2021 |
| Over Seas Apparel Ltd | Wholesale & retail | 2021 |
| Over the Line Consulting Ltd | Professional & scientific | 2022 |
| Overall Developments Limited | Administrative & support | 2008 |
| Overcast Technologies Limited | Information & communication | 2024 |
| Overflow Ltd | Administrative & support | 2024 |
| Overhirst Limited | Wholesale & retail | 2010 |
| Overland Property Ltd | Real estate | 2016 |
| Overlord Creations Ltd | Information & communication | 2025 |