| Ogac Ltd | Construction | 2024 |
| Ogle Baker Limited | Wholesale & retail | 2024 |
| Ogold Ltd | Information & communication | 2025 |
| OH Candy Limited | Information & communication | 2014 |
| OHD Global Health and Social Care Solutions Limited | Health & social care | 2024 |
| Ohealio Ltd | Information & communication | 2021 |
| Oikoso Ltd | Wholesale & retail | 2024 |
| OJ Neil Holdings Limited | Financial services | 2025 |
| Okmonkeys Ltd | Information & communication | 2026 |
| OKO Protein Ltd | Manufacturing | 2022 |
| OKY Ltd | Wholesale & retail | 2025 |
| Olade Capital Ltd | Financial services | 2026 |
| Olade Holdings Ltd | Financial services | 2026 |
| Olafusion Properties Ltd | Real estate | 2025 |
| Olcd Management Consultants Ltd | Professional & scientific | 2025 |
| Old Moat Hall Limited | Construction | 2025 |
| Old School Tutoring Limited | Education | 2016 |
| Old Stables Yard Management Company Limited | Real estate | 2012 |
| Old Tiger HAY & Haylage Ltd | Wholesale & retail | 2021 |
| Oldash@Home Ltd | Real estate | 2022 |
| Oleco Limited | Construction | 2018 |
| OLF Group Limited | Real estate | 2025 |
| Olindo Group Ltd | Hospitality | 2023 |
| Oliva Pottery Ltd | Arts & recreation | 2025 |
| Olivara Group Limited | Wholesale & retail | 2025 |
| Olive and Pinch Ltd | Wholesale & retail | 2024 |
| Olive Door Community CIC | Administrative & support | 2023 |
| Olivearne Capital Holdings Ltd | Manufacturing | 2022 |
| Oliver James Group Ltd | Wholesale & retail | 2024 |
| Olivia IS Online Limited | Manufacturing | 2021 |
| Olivia Jacobs Kitchens & Bathrooms Ltd | Construction | 2019 |
| Olivian Group Ltd | Information & communication | 2026 |
| Oliviarae Limited | Construction | 2022 |
| Oliviaraedevelopments Ltd | Real estate | 2024 |
| Olivz Properties Ltd | Real estate | 2025 |
| Ollands Farming Limited | Agriculture & fishing | 2022 |
| Ollbec Ltd | Real estate | 2025 |
| Ollie Ford & Company Ltd | Information & communication | 2010 |
| Olthem Payments Ltd | Financial services | 2017 |
| Oluwaseni Fawehinmi Limited | Administrative & support | 2021 |
| Oluwaseni Fisayo Fawehinmi Limited | Extraterritorial | 2021 |
| Olympus Premium Health Ltd | Manufacturing | 2021 |
| Olypon Ltd | Information & communication | 2026 |
| OM Health and Wellbeing Consultancy Ltd | Administrative & support | 2017 |
| Omar AL Madani Investments Ltd | Energy | 2025 |
| Omar Khan Enterprises Limited | Real estate | 2018 |
| Omarihsan Ltd | Wholesale & retail | 2023 |
| Omark Group Ltd | Financial services | 2025 |
| Omega Parking Ltd | Transport & logistics | 2025 |
| Omega Properties(Suffolk) Ltd | Wholesale & retail | 2016 |
| Omega Property Development Ltd | Real estate | 2022 |
| Omega Snacks Ltd | Hospitality | 2011 |
| Omerbeyoglu Unlu Ltd | Information & communication | 2025 |
| OMH Associates Limited | Professional & scientific | 2023 |
| OML Consulting Limited | Professional & scientific | 2022 |
| Omni Wellness Ltd | Wholesale & retail | 2026 |
| Omnia Core Creative Limited | Information & communication | 2017 |
| Omnia Group Solutions Ltd | Real estate | 2025 |
| Omnibridge Works Limited | Professional & scientific | 2026 |
| Omniguard Solutions Ltd | Information & communication | 2025 |
| Omniphase Electrical Ltd | Construction | 2026 |
| Omnity Technologies Ltd | Information & communication | 2025 |
| Omnx Limited | Manufacturing | 2025 |
| Omonoki.Com Ltd | Information & communication | 2025 |
| Omosede C Odijie Ltd | Hospitality | 2023 |
| Omsco Ltd | Professional & scientific | 2021 |
| ON Point Tennis Limited | Arts & recreation | 2023 |
| ON Retreat Ltd | Other services | 2024 |
| ON Schedule Deliveries Ltd | Transport & logistics | 2023 |
| ON SET Artificial Grass Ltd | Construction | 2026 |
| ON Solutions Ltd | Other services | 2020 |
| ON the Cake Stand Limited | Hospitality | 2021 |
| ON Your Terms Media LLP | | 2025 |
| Onaney Ltd | Wholesale & retail | 2026 |
| Once Upon a TAG Ltd | Wholesale & retail | 2025 |
| One Ahead Ltd | Information & communication | 2022 |
| One Call Plumbing Emergencies Ltd | Construction | 2025 |
| One Lease Ltd | Administrative & support | 2025 |
| One Mercantile Limited | Wholesale & retail | 2025 |
| One Piece Holdings Ltd | Financial services | 2026 |
| One Piece Management Ltd | Real estate | 2026 |
| One Piece Properties Ltd | Real estate | 2026 |
| One Rectangle Ltd | Information & communication | 2024 |
| One Technician Limited | Information & communication | 2018 |
| ONE12 Grpx Ltd | Information & communication | 2026 |
| Oneehide Ltd | Wholesale & retail | 2024 |
| Onefigure Gifts Ltd | Wholesale & retail | 2024 |
| Onefourseven Digital Limited | Information & communication | 2025 |
| Onemach World Trade Ltd | Wholesale & retail | 2026 |
| Onestar Tech Ltd | Information & communication | 2025 |
| Onewaypass Ltd | Information & communication | 2025 |
| Onezeroseven Properties Limited | Real estate | 2018 |
| Online Catalyst Ltd | Administrative & support | 2024 |
| Only Good Limited | Professional & scientific | 2025 |
| Only Paper Limited | Manufacturing | 2019 |
| Only Van’S - Wigan Ltd | Wholesale & retail | 2025 |
| Onnu Green Hub Ltd | Water & waste | 2024 |
| Onsite Hire Limited | Administrative & support | 2012 |
| Ontrack Logistics Ltd | Transport & logistics | 2025 |
| Onxy Management Ltd | Hospitality | 2026 |