| OCD Records Ltd | Information & communication | 2014 |
| Ocean Acres Ltd | Agriculture & fishing | 2024 |
| Ocean Breeze Tourism Ltd | Administrative & support | 2025 |
| Ocean Exim Ltd | Wholesale & retail | 2025 |
| Ocean Jasper Ltd | Wholesale & retail | 2020 |
| Ocean Rain Properties Ltd | Real estate | 2022 |
| Ocean Smiles Ltd | Real estate | 2022 |
| Ocean Ventures Yacht Ltd | Transport & logistics | 2026 |
| Ocean View Travel Limited | Administrative & support | 2024 |
| OCG Creations Ltd | Construction | 2025 |
| OCI Cards Ltd | Professional & scientific | 2022 |
| Ocker Limited | Transport & logistics | 2016 |
| Ockham Ltd | Professional & scientific | 2011 |
| Oclean Dist Ltd | Wholesale & retail | 2023 |
| Ocram Development Limited | Construction | 2018 |
| Ocrans Ltd | Construction | 2020 |
| Octagon Impact Ltd | Construction | 2025 |
| Octane Management Consultants Limited | Professional & scientific | 2015 |
| Octane Software Solutions Ltd | Information & communication | 2022 |
| Octavia Leisure Ltd | Hospitality | 1998 |
| Octavian Lifting Ltd | Water & waste | 2026 |
| Octavian Limited | Transport & logistics | 2018 |
| Octochip Ltd | Information & communication | 2025 |
| Octopus Builders Ltd | Construction | 2025 |
| Ocular Holdings Limited | Professional & scientific | 2023 |
| Ocular Technologies Limited | Information & communication | 2022 |
| Odessa Rotherham Ltd | Real estate | 2021 |
| ODG Plant Hire Limited | Administrative & support | 2002 |
| Odontologica Limited | Health & social care | 2018 |
| Odontotek Medical Ltd | Health & social care | 2026 |
| Odris Holdings Limited | Financial services | 2016 |
| Odris Investments Limited | Administrative & support | 2015 |
| Odyssey Projects Limited | Professional & scientific | 2002 |
| Odyssey Utilities (UK) Ltd | Construction | 2017 |
| Odýsseia Digital Limited | Information & communication | 2023 |
| Oecm Limited | Construction | 2026 |
| Oecophy Ltd | Wholesale & retail | 2017 |
| OFF the Pitch Limited | Information & communication | 2024 |
| Office on the Hill Limited | Real estate | 2006 |
| Office Overload Limited | Administrative & support | 1966 |
| Offshore Task Accounting Services Limited | Administrative & support | 2022 |
| Offshore Workforce Solutions UK Ltd | Information & communication | 2023 |
| Offthefairway Apparel Ltd | Wholesale & retail | 2025 |
| OG Building Ltd | Construction | 2019 |
| OG Fire and Security Limited | Administrative & support | 2026 |
| Ogarit Limited | Wholesale & retail | 2024 |
| Ogde Limited | Professional & scientific | 2016 |
| Ogilvie Analytics Limited | Information & communication | 2026 |
| OGO IT Consulting Ltd | Information & communication | 2024 |
| OH My Shrooms Ltd | Manufacturing | 2018 |
| OH! EV Ltd | Transport & logistics | 2022 |
| OHD Ventures Ltd | Real estate | 2022 |
| OHM Associates Limited | Construction | 2012 |
| OHM Construction Limited | Construction | 1993 |
| Oike Properties Ltd | Real estate | 2025 |
| Oikos Ltd | Real estate | 2017 |
| Oils and Sprays Ltd | Wholesale & retail | 2021 |
| Oishi Investment Group Ltd | Financial services | 2025 |
| Oisin Rogers Limited | Professional & scientific | 2012 |
| OJ Logistics & Services Ltd | Transport & logistics | 2026 |
| Ojas Health Ltd | Health & social care | 2023 |
| Ojas Holdings Limited | Real estate | 2019 |
| Ojas Property Consultants Limited | Real estate | 2020 |
| Ojash Limited | Wholesale & retail | 2016 |
| OJO Drylining Ltd | Construction | 2020 |
| OK Enterprises Ltd | Hospitality | 2024 |
| OK Plumbing and Heating Limited | Construction | 2020 |
| Okiniya Limited | Hospitality | 2015 |
| Okland Limited | Hospitality | 2025 |
| Okoffi Limited | Administrative & support | 2007 |
| OKX Limited | Health & social care | 2024 |
| Olaf Engine Spares Limited | Wholesale & retail | 2018 |
| Olaf Enterprise Limited | Wholesale & retail | 2014 |
| Olanescu Ltd | Construction | 2026 |
| Olbury Ltd | Education | 2021 |
| Old Beams Development and Sales Limited | Construction | 2026 |
| Old Bills Pest Control Limited | Administrative & support | 2017 |
| Old Macdonald's Bourne END Limited | Education | 2026 |
| Old Macdonald's Leverstock Green Limited | Education | 2025 |
| Old Mill Management NO.1 Limited | Households | 2011 |
| Old Oak W3 Limited | Construction | 2020 |
| Old Rectory (Bramshall) Ltd | Health & social care | 2005 |
| OLI Investments Limited | Real estate | 2016 |
| OLI Pictures Limited | Administrative & support | 2020 |
| Olio Cars Limited | Transport & logistics | 2017 |
| Oliva Casa Ltd. | Real estate | 2022 |
| Oliva Vista LLP | | 2024 |
| Olive Branch Fostering Ltd | Health & social care | 2015 |
| Oliver B Magic Limited | Administrative & support | 2016 |
| Oliver Haddon Designs Limited | Manufacturing | 2017 |
| Oliver Hodgson Ltd | Construction | 2013 |
| Oliver Knight Limited | Professional & scientific | 2007 |
| Oliver Pattisson Arts Ltd | Wholesale & retail | 2018 |
| Oliver Reeves Properties Limited | Construction | 2018 |
| Olivewood Holdings Ltd | Wholesale & retail | 2024 |
| Olivewood Limited | Wholesale & retail | 1995 |
| Olivewood Properties Limited | Real estate | 2020 |
| Olivia Fernande Elizabeth Duckworth Ltd | Extraterritorial | 2023 |
| Olivia Fernande Elizabeth Mann Limited | Extraterritorial | 2024 |
| Olivine Studios Ltd | Professional & scientific | 2022 |