| OC Electric Limited | Construction | 2016 |
| OC Learning Limited | Education | 2020 |
| OC329702 LLP | | 2007 |
| Ocawa Ltd | Wholesale & retail | 2024 |
| Ocaya Building Contractors Ltd | Construction | 2019 |
| OCB Aesthetics Ltd | Health & social care | 2023 |
| Occasian DJS Ltd | Arts & recreation | 2023 |
| Occiprae Ltd | Information & communication | 2025 |
| Occupational Hygiene Monitoring Limited | Administrative & support | 2015 |
| Occupational Therapy Solutions Limited | Professional & scientific | 2024 |
| Ocean Breeze Crafts Ltd | Wholesale & retail | 2025 |
| Ocean Buildings (Cardiff) RTM Company Limited | Real estate | 2012 |
| Ocean Business Supplies Limited | Wholesale & retail | 2003 |
| Ocean Coffee Ltd | Hospitality | 2019 |
| Ocean Community Services Limited | Health & social care | 2005 |
| Ocean Consolidated Properties Limited | Real estate | 2011 |
| Ocean Cooling Ltd | Construction | 2017 |
| Ocean Dream Corporation Ltd | Professional & scientific | 2016 |
| Ocean Facilities Limited | Education | 2016 |
| Ocean Generation International Ltd | Administrative & support | 2016 |
| Ocean Independent Limited | Arts & recreation | 2003 |
| Ocean Leap Limited | Wholesale & retail | 2025 |
| Ocean Outfitters Limited | Wholesale & retail | 2014 |
| Ocean Portfolio LLP | | 2011 |
| Ocean Promote Foods Co., Ltd | Professional & scientific | 2012 |
| Ocean Pubs Ltd | Hospitality | 2020 |
| Ocean Reach Ltd | Households | 2010 |
| Ocean Refresh.Com Ltd | Manufacturing | 2019 |
| Oceanarc Limited | Other services | 2012 |
| Oceanic Equity Ltd. | Professional & scientific | 2012 |
| Oceanical Limited | Administrative & support | 2015 |
| Oceans Maltby Ltd | Hospitality | 2019 |
| Oceans Maltby Xpress Ltd | Hospitality | 2019 |
| Oceanus Consulting Ltd | Wholesale & retail | 2025 |
| Ocenew Ltd | Wholesale & retail | 2025 |
| Ocevara Ltd | Wholesale & retail | 2025 |
| Ochr Olau Ltd | Extraterritorial | 2014 |
| Ochre Verge Ltd | Wholesale & retail | 2026 |
| Ociale Services Ltd | Wholesale & retail | 2021 |
| OCM London Limited | Real estate | 2015 |
| Oconn Limited | Construction | 2021 |
| Oconnor Stone Limited | Construction | 2013 |
| Oconnorcaravans Ltd | Wholesale & retail | 2025 |
| OCS Heating and GAS Group Ltd | Construction | 2023 |
| OCT Contract Services Ltd | Administrative & support | 2019 |
| Octacore Solutions PVT Ltd | Information & communication | 2021 |
| Octalware International Ltd | Information & communication | 2014 |
| Octane Homes Limited | Construction | 2023 |
| Octanexus Limited | Administrative & support | 2022 |
| Octavia Builders Ltd | Construction | 2014 |
| Octo Ltd | Administrative & support | 2018 |
| Octo Partners Limited | Energy | 2019 |
| October October Limited | Information & communication | 2024 |
| Octogon Limited | Financial services | 2017 |
| Octopus Clean Ltd | Administrative & support | 2026 |
| Octopus SBI Consulting Limited | Administrative & support | 2021 |
| Octoswap Invest Ltd | Wholesale & retail | 2025 |
| Ocuair Limited | Information & communication | 2014 |
| Oculus Care Ltd | Health & social care | 2016 |
| Oculus Design and Build Ltd | Construction | 2020 |
| Oculus Estates Ltd | Real estate | 2017 |
| Oculus Investments Ltd | Real estate | 2017 |
| Oculus Key Limited | Real estate | 2014 |
| Oddball Tours Ltd | Hospitality | 2018 |
| Odendaal Homes Ltd | Real estate | 2018 |
| Odera OIL Field Services Limited | Professional & scientific | 2007 |
| ODF Clothing - One Diverse Fashion Ltd | Wholesale & retail | 2020 |
| Odin Refrigeration and Air Conditioning Ltd | Manufacturing | 2021 |
| Odin Sales Ltd | Wholesale & retail | 2024 |
| Odintech Advisory Ltd | Information & communication | 2025 |
| Odis Systems Ltd | Information & communication | 2023 |
| ODJ Consulting Ltd | Professional & scientific | 2025 |
| Odnova Ltd | Other services | 2020 |
| Odofa Enterprise Limited | Wholesale & retail | 2026 |
| Odonata International Limited | Manufacturing | 2020 |
| Odonto Limited | Health & social care | 2013 |
| Odoryxell Ltd | Wholesale & retail | 2025 |
| Odysseus Group Ltd | Professional & scientific | 2018 |
| Odyssey Administration Limited | Financial services | 2018 |
| Odyssey Legal Services Limited | Professional & scientific | 2004 |
| Odyssey Pensions Limited | Financial services | 2017 |
| Odyssey Sipp Limited | Financial services | 2018 |
| Odyssey Ssas Limited | Financial services | 2018 |
| OE 18 Limited | Hospitality | 2021 |
| OEF Property Group Ltd | Real estate | 2026 |
| OEI Paris Limited | Construction | 2019 |
| OES Gafr ETO CYF | Wholesale & retail | 2024 |
| Oewshs Ltd | Manufacturing | 2026 |
| Oferro Ltd | Administrative & support | 2023 |
| OFF and on (the Vale) Limited | Construction | 2017 |
| OFF CUT Ltd | Administrative & support | 2011 |
| OFF the Grid Electrical Ltd | Construction | 2019 |
| Offa Power Limited | Energy | 2012 |
| Offbeat Drinks Ltd | Wholesale & retail | 2019 |
| Offbeat Limited | Manufacturing | 2009 |
| Offcumdens Ltd | Extraterritorial | 2021 |
| Office Blinds Direct Ltd | Manufacturing | 2021 |
| Office INK Ltd | Wholesale & retail | 2025 |
| Offpitch Sports International Ltd | Professional & scientific | 2025 |
| Offseason NG1 Limited | Wholesale & retail | 2022 |