| OG Games Ltd | Wholesale & retail | 2009 |
| Ogilvy Solutions Limited | Administrative & support | 2015 |
| Ogleforth Management Company Limited | Real estate | 2010 |
| Oglesby M.D.S. Limited | Professional & scientific | 2019 |
| Ogleyyt Ltd | Manufacturing | 2025 |
| OH My Gosh! Nails Limited | Other services | 2022 |
| OHC Capital Limited | Financial services | 2012 |
| OHC Property One Limited | Real estate | 2011 |
| Ohsec Limited | Professional & scientific | 2024 |
| OIL Slick Dispersants Limited | Manufacturing | 1997 |
| OJW Racing Ltd | Arts & recreation | 2025 |
| Okerpharma Consultancy Limited | Health & social care | 2007 |
| Oknoplast UK Limited | Wholesale & retail | 2025 |
| Olaya Ltd | Real estate | 2023 |
| Old Boys Development Limited | Construction | 2024 |
| Old Buck Inn Property Ltd | Real estate | 2017 |
| Old Cornmill Staveley Paddock Limited | Agriculture & fishing | 2009 |
| Old Malt Kiln Management Co Limited | Households | 2021 |
| Old Mill (Wetherby) Management Company Limited | Households | 1992 |
| Old Oak Tree Limited | Hospitality | 2010 |
| Old Palace Management Co. Limited | Households | 1997 |
| Old Pale Heights Management Company Limited | Administrative & support | 2004 |
| Old Pasture Park Limited | Hospitality | 2020 |
| Old Priory Court (York) Management Company Ltd | Households | 1999 |
| Old Rope Limited | Wholesale & retail | 1980 |
| Old School Ltd | Hospitality | 2017 |
| Oldrl Ltd | Wholesale & retail | 2020 |
| Oldstead Aero LLP | | 2018 |
| Oleria Limited | Wholesale & retail | 2020 |
| Olicana Solutions Ltd. | Information & communication | 2011 |
| Olimax Motorhome Hire Ltd | Administrative & support | 2021 |
| Olimax Van Hire Limited | Administrative & support | 2024 |
| Olitra Leisure Ltd | Hospitality | 2021 |
| Olivedon Ltd | Administrative & support | 2007 |
| Oliver Business Services Ltd | Information & communication | 2024 |
| Oliver Craske Electrical Contractor Limited | Manufacturing | 2008 |
| Oliver Interiors York Ltd | Construction | 2025 |
| Oliver Kemp Limited | Extraterritorial | 2024 |
| Oliver Mews Management Company (York) Limited | Households | 1987 |
| Oliver Órla Property Investments Ltd | Real estate | 2022 |
| Olivia Brabbs Photography Limited | Professional & scientific | 2016 |
| Olivia Thompson Limited | Arts & recreation | 2024 |
| Olivia’S Tearoom Limited | Hospitality | 2023 |
| Ollie Homes Limited | Real estate | 2019 |
| Olsson Investments Limited | Real estate | 2022 |
| Olujay & Co Limited | Financial services | 2016 |
| OM Preloved Ltd | Wholesale & retail | 2025 |
| Omega Business Consulting Limited | Professional & scientific | 2024 |
| Omega Industrial Village (Northallerton) Limited | Extraterritorial | 2009 |
| Omni Wellness Group Limited | Arts & recreation | 2022 |
| Omnie AI Ltd | Information & communication | 2024 |
| Omnie Ltd | Wholesale & retail | 2009 |
| Omoni House Limited | Hospitality | 2022 |
| Omrax Limited | Wholesale & retail | 2016 |
| Omrax Property Management Ltd | Real estate | 2019 |
| OMS Racing LLP | | 2010 |
| OMT Consulting Ltd | Professional & scientific | 2014 |
| Omwani Coffee Company Ltd | Wholesale & retail | 2019 |
| ON a Plod Ltd | Arts & recreation | 2025 |
| ON Box Gaming Ltd | Wholesale & retail | 2021 |
| ON the Fence (York) Limited | Wholesale & retail | 2015 |
| ON the Hill Leisure Limited | Arts & recreation | 2026 |
| ON the Shire Ltd | Hospitality | 2021 |
| ON Top Projects Ltd | Construction | 2022 |
| ON Top Racing Ltd | Construction | 2023 |
| ON Top Slating Ltd | Construction | 2022 |
| Onbasi Foods Limited | Hospitality | 2025 |
| Oncommerce Limited | Professional & scientific | 2026 |
| Oncosense Limited | Manufacturing | 2025 |
| One 4 ALL Supermarket (York) Ltd | Wholesale & retail | 2025 |
| One Big Table Limited | Professional & scientific | 2025 |
| One Booking Ltd | Information & communication | 2025 |
| One Equity Ltd. | Financial services | 2024 |
| One House Booking Ltd | Real estate | 2024 |
| One IT Consulting Limited | Information & communication | 2020 |
| One SIP Cafe Ltd | Hospitality | 2025 |
| One Stop (UK) Shop Limited | Wholesale & retail | 2013 |
| One Stop Business Capital Limited | Extraterritorial | 2017 |
| One Stop Business Finance 2 Limited | Financial services | 2021 |
| One Stop Business Finance Limited | Financial services | 2014 |
| One Stop Business Finance SPV 2 Limited | Financial services | 2023 |
| One Stop Business Finance SPV 3 Limited | Financial services | 2024 |
| One Stop Business Finance SPV Limited | Financial services | 2018 |
| One Stop Business Group Holdings Limited | Financial services | 2025 |
| One Stop Business Group Limited | Financial services | 2007 |
| One Stop Business Property Limited | Real estate | 2020 |
| One Stop Finance Professionals Limited | Professional & scientific | 2012 |
| One Stop Invoice Finance Limited | Financial services | 2022 |
| One Team Tech Limited | Information & communication | 2025 |
| One Two Solutions Limited | Information & communication | 2007 |
| One Two Two Holgate Ltd | Financial services | 2022 |
| ONE1STAR Solutions Limited | Manufacturing | 2019 |
| Onebright Efficacy Limited | Administrative & support | 2007 |
| Onebright Group Limited | Financial services | 2019 |
| Onebright Limited | Health & social care | 2015 |
| Onebright Midco Limited | Financial services | 2019 |
| Onebright Oscar Limited | Financial services | 2021 |
| Onebright Psychiatric Services Ltd | Health & social care | 2022 |
| Onebright Systems Limited | Information & communication | 2009 |
| Onebright UK Holdco Limited | Financial services | 2019 |