| Observation Wheel (UK) Ltd | Arts & recreation | 2017 |
| Observer Basement Limited | Construction | 2022 |
| OBT Digital Ltd | Information & communication | 2023 |
| OC372453 LLP | | 2012 |
| Ocampo Clinics Limited | Other services | 2025 |
| Occupational Psychology Solutions Ltd | Professional & scientific | 2009 |
| OCD (Wirral) Limited | Administrative & support | 2017 |
| OCD Commercial Limited | Administrative & support | 2024 |
| OCD Group Limited | Administrative & support | 2021 |
| Ocean Bathrooms and Kitchens Limited | Construction | 2019 |
| Ocean Data Logic Limited | Administrative & support | 2013 |
| OCEAN22 Properties Ltd | Real estate | 2022 |
| Oceania Engineering Limited | Professional & scientific | 2021 |
| Oceanix-Uk Ltd | Information & communication | 2015 |
| OCL 1 Limited | Real estate | 2018 |
| OCM Consultants Limited | Administrative & support | 2016 |
| Ocpc Ltd | Professional & scientific | 2019 |
| OCT Construction Ltd | Construction | 2023 |
| OCT Plant Hire Limited | Administrative & support | 2025 |
| Octagon Engineering Services Ltd | Professional & scientific | 2019 |
| Octave Investments Limited | Financial services | 2020 |
| Octavia IT Consulting Ltd | Information & communication | 2023 |
| Octavia Property Ltd | Real estate | 2024 |
| Octawave Studios Limited | Manufacturing | 2020 |
| Octogreen Ltd | Transport & logistics | 2019 |
| Octovian Ltd | Information & communication | 2020 |
| Octrax Limited | Other services | 2017 |
| Octron Ltd | Information & communication | 2025 |
| OCU International Limited | Wholesale & retail | 2025 |
| Ocuheat Limited | Construction | 2025 |
| Oculoplastics Inc. Limited | Health & social care | 2023 |
| Odaat Clobber Ltd | Professional & scientific | 2022 |
| Odin Fitness Limited | Arts & recreation | 2014 |
| Odin Insulation Solutions Limited | Manufacturing | 2024 |
| Odinham Ltd | Construction | 2022 |
| ODM Solutions Ltd | Administrative & support | 2010 |
| Odmac Limited | Information & communication | 2011 |
| Odonata Project Managment Limited | Administrative & support | 2023 |
| ODR Consultancy Ltd | Professional & scientific | 2024 |
| Oeconomus Consilio Ltd | Administrative & support | 2023 |
| Oehman Consulting Limited | Professional & scientific | 2018 |
| Oem-Only Ltd | Wholesale & retail | 2019 |
| OES Prime Ltd | Wholesale & retail | 2025 |
| OFA Building & Groundworks Ltd | Construction | 2020 |
| OFA Projects Management Limited | Construction | 2018 |
| OFF Market Property Group Limited | Other services | 2022 |
| OFF the Wall Cars Limited | Professional & scientific | 2019 |
| OFF the Wall Communications Limited | Administrative & support | 2019 |
| OFF Your Marks Ltd | Wholesale & retail | 2007 |
| Office Inspired Limited | Wholesale & retail | 2015 |
| Office Installation Services Limited | Administrative & support | 1997 |
| Office Installations (Bristol) Limited | Construction | 2005 |
| Offshore Wind Cost Solutions Ltd | Information & communication | 2023 |
| Offside Agency Ltd | Wholesale & retail | 2018 |
| Offworld Holdings Ltd | Information & communication | 2026 |
| OFM Cloudlogic Solutions Limited | Information & communication | 2019 |
| Oggi Engineering Limited | Administrative & support | 2016 |
| Ogmsatellite Ltd | Information & communication | 2013 |
| OH Bespoke Limited | Construction | 2023 |
| OH Dormant Ltd | Real estate | 2010 |
| OH That's Wicked Registrations Limited | Hospitality | 2019 |
| Ohayo UK Ltd | Wholesale & retail | 2022 |
| Ohio Tax Ltd | Professional & scientific | 2022 |
| Ohms Property Holding Limited | Financial services | 2025 |
| Ohms Property Limited | Real estate | 2025 |
| Oilzart Ltd | Arts & recreation | 2023 |
| OJ UK Transport Limited | Transport & logistics | 2018 |
| OJB Consultancy Limited | Professional & scientific | 2022 |
| OJM Real Estate Legal Ltd | Professional & scientific | 2026 |
| Ojojo Ltd | Wholesale & retail | 2022 |
| OK MUM (UK) Limited | Other services | 2009 |
| Okel Ltd | Manufacturing | 2010 |
| Okeover Enterprises Limited | Energy | 1981 |
| Okten Building Services Ltd | Construction | 2021 |
| Olal Consultancy Services Limited | Professional & scientific | 2019 |
| Olam Holdings Ltd | Real estate | 2017 |
| Old County PO Station Limited | Real estate | 2017 |
| Old Iron Rides Ltd | Wholesale & retail | 2020 |
| Old Lodge Farm Ltd. | Real estate | 2016 |
| Old PO Building Limited | Real estate | 2015 |
| Old School Creative Ltd | Information & communication | 2020 |
| Old Trees Capital Limited | Financial services | 2022 |
| Old Trees Capital Partners Ltd | Financial services | 2022 |
| Oldbury Grove Limited | Administrative & support | 2019 |
| Oldfield Simmons Limited | Professional & scientific | 2007 |
| Oldrich Janosek Ltd | Administrative & support | 2025 |
| OLEC4U Ltd | Construction | 2016 |
| Olenar Holdings Ltd | Construction | 2025 |
| Oleve Consulting Limited | Administrative & support | 2015 |
| Olexa Haulage Ltd | Transport & logistics | 2020 |
| OLI Projects Limited | Information & communication | 2013 |
| Olibelle Limited | Real estate | 2024 |
| Olidya Ltd | Wholesale & retail | 2020 |
| Olimpia&Kuki Ltd | Administrative & support | 2024 |
| Oliphip Resources Limited | Health & social care | 2024 |
| Olive Asia Mart Ltd | Wholesale & retail | 2024 |
| Olive the PUG Ltd | Information & communication | 2021 |
| Olive Tree Photography Ltd | Professional & scientific | 2019 |
| Oliveira Teleradiology Ltd | Administrative & support | 2025 |
| Oliver George Consultancy Ltd | Administrative & support | 2025 |