| OLA Ademola Consulting Limited | Professional & scientific | 2017 |
| Olak Animashaun Healthcare Services Ltd | Health & social care | 2019 |
| Olam LYF Ltd | Hospitality | 2025 |
| Olamot Ltd | Hospitality | 2020 |
| Olart Nurture Homes Ltd | Health & social care | 2026 |
| Olatunde Ashaolu Associates Ltd | Professional & scientific | 2010 |
| Olayemi & Co. Ltd | Health & social care | 2021 |
| Ola’S Entertainment Ltd | Administrative & support | 2025 |
| Olberon Design Consultancy Limited | Professional & scientific | 2017 |
| Old Barber Shop Ltd | Other services | 2018 |
| Old Dairy Farm Limited | Households | 2007 |
| Old England Homes Group Ltd | Real estate | 2016 |
| Old Folks Limited | Hospitality | 2020 |
| Old Ginger Developments Limited | Construction | 1997 |
| Old Kent Road E-Foods Ltd. | Hospitality | 2021 |
| Old Middleton Management Company Ltd | Households | 2017 |
| Old Park Farm (Toddington) Limited | Agriculture & fishing | 2016 |
| Old School House (Northampton) Limited | Real estate | 1994 |
| Old Station Joinery Ltd | Manufacturing | 2019 |
| Old Station Management Company Limited | Real estate | 2017 |
| Oldama Electrical Contractor Limited | Construction | 2014 |
| Olde Cobbler Limited | Hospitality | 2019 |
| Olde PUB Grub Co. Limited | Wholesale & retail | 2026 |
| Older & Wilder Ltd | Administrative & support | 2020 |
| Oldershaw Cabling Services Limited | Extraterritorial | 2024 |
| Oleg Cebotaru Limited | Manufacturing | 2025 |
| Olega Property Management Limited | Households | 2026 |
| Olegs Emporio Limited | Transport & logistics | 2012 |
| OLI Bowden Scaffolding Services Limited | Construction | 2022 |
| Oli's Barber Shop Ltd | Other services | 2022 |
| Olie&Co Limited | Professional & scientific | 2017 |
| Oliproperties Ltd | Real estate | 2024 |
| Olive and Baker Limited | Hospitality | 2023 |
| Olive Branch and Delights Limited | Manufacturing | 2024 |
| Olive Grove Solutions Limited | Professional & scientific | 2023 |
| Oliveira Wines Limited | Wholesale & retail | 2023 |
| Oliver Adams Investments Limited | Construction | 2016 |
| Oliver Christies Children’S Services Limited | Health & social care | 2023 |
| Oliver Dean Ltd | Real estate | 2023 |
| Oliver Gavin Limited | Arts & recreation | 1990 |
| Oliver James Estate Agents Limited | Real estate | 1999 |
| Oliver's Hire Solutions Ltd | Construction | 2022 |
| OLIVER17 Ltd | Real estate | 2022 |
| Olivetti UK Limited | Wholesale & retail | 1974 |
| Olivia Estebanez Limited | Administrative & support | 2015 |
| Olivia House Developments Limited | Construction | 2002 |
| Oliviabhome Limited | Real estate | 2026 |
| Olleco | Manufacturing | 2006 |
| Ollopaco Limited | Wholesale & retail | 2019 |
| Ollymores Limited | Public administration | 2022 |
| Olmar Investments Limited | Wholesale & retail | 1957 |
| Olney Hair and Beauty Limited | Extraterritorial | 2023 |
| Olney House of Beauty Limited | Other services | 2015 |
| Olney Spa Limited | Other services | 2018 |
| Olneyrugs Ltd | Administrative & support | 2018 |
| Olori Fabrics & More Limited | Wholesale & retail | 2025 |
| Olshan Property Ltd | Real estate | 2024 |
| Oluchi Cosmetics Limited | Health & social care | 2022 |
| Oluronbi Limited | Health & social care | 2020 |
| Oluwaseun Limited | Administrative & support | 2013 |
| Oluwatosin Consultancy Ltd | Information & communication | 2026 |
| Olwell Limited | Real estate | 2005 |
| OM & Shivani Ltd | Real estate | 2026 |
| OM NSP Foods Ltd | Wholesale & retail | 2023 |
| Omabo International Resources Ltd | Wholesale & retail | 2025 |
| Omanba Limited | Extraterritorial | 2023 |
| Omash Holdings Ltd | Real estate | 2024 |
| OME Power Services Ltd | Energy | 2024 |
| Omega 4 Labs Ltd | Information & communication | 2025 |
| Omega Infinite PLC | Financial services | 2014 |
| Omfinitive Ltd | Information & communication | 2026 |
| OMG Consultants Limited | Wholesale & retail | 2017 |
| OMG PS Ltd | Professional & scientific | 2013 |
| OMG Trading Limited | Wholesale & retail | 2017 |
| Omimo Ltd | Wholesale & retail | 2024 |
| Omnia Transports Ltd | Transport & logistics | 2023 |
| Omnitech Business Ltd | Information & communication | 2013 |
| Omnyr Technologies Ltd | Information & communication | 2026 |
| Omran Homes Limited | Construction | 2025 |
| Omrok Ltd | Wholesale & retail | 2025 |
| OMT Transport Ltd | Transport & logistics | 2019 |
| Omur Pharmaceutical & Cosmetics Ltd | Wholesale & retail | 2026 |
| ON Call Cleaning Services Limited | Administrative & support | 2021 |
| ON Call Driver Ltd | Transport & logistics | 2025 |
| ON Demand Print Services Limited | Manufacturing | 2003 |
| ON Eight Limited | Real estate | 2012 |
| ON Point Bricklayers Ltd | Construction | 2017 |
| ON the Ball Paving Limited | Construction | 2023 |
| ON the MAP Northamptonshire | Administrative & support | 2026 |
| ON the Rocks (IOW) Ltd | Hospitality | 2018 |
| ON the Shore Productions Ltd | Arts & recreation | 2023 |
| On-Load Systems Limited | Construction | 2010 |
| On-Site Group Global Limited | Professional & scientific | 2019 |
| Once Solutions UK Limited | Administrative & support | 2010 |
| Oncosol Limited | Manufacturing | 2015 |
| One Auto Recruit (UK) Ltd | Administrative & support | 2023 |
| One Avenue Ltd | Other services | 2016 |
| One Business Day Ltd | Professional & scientific | 2021 |
| One Digital Limited | Manufacturing | 2003 |
| One Eight Mart Ltd | Wholesale & retail | 2026 |