| Oakham Cranford Limited | Professional & scientific | 2013 |
| Oakham Creations Limited | Wholesale & retail | 2021 |
| Oakham Fleet Solutions Limited | Professional & scientific | 2022 |
| Oakham Green Properties Ltd | Real estate | 2025 |
| Oakham Hill Home & Garden Limited | Construction | 2019 |
| Oakham Lift Services & Components Ltd | Manufacturing | 2026 |
| Oakham Research Limited | Professional & scientific | 2011 |
| Oakham Surfacing & Construction Ltd | Construction | 2019 |
| Oakhaminteriors Ltd | Construction | 2026 |
| Oakhampton (Hilton) Management Company Limited | Households | 2006 |
| Oakhill Optical Limited | Manufacturing | 2015 |
| OAS Services Ltd | Administrative & support | 2025 |
| Oasis Homes (Midlands) Limited | Construction | 2014 |
| Oasis Pizza and Kebab Ltd | Hospitality | 2022 |
| OBA One International Limited | Real estate | 2025 |
| Obhealthcare Ltd | Administrative & support | 2024 |
| Ocean Fish & Chips (West Midlands) Limited | Hospitality | 2023 |
| Ocean View (Rhodes) Limited | Real estate | 2017 |
| Ocean-Rock International Ltd | Real estate | 2024 |
| OCS Oriana Cleaning Services Limited | Administrative & support | 2021 |
| Octopus Bathrooms Limited | Wholesale & retail | 2015 |
| Oculare AI Limited | Professional & scientific | 2019 |
| Odima Care Services Limited | Health & social care | 2019 |
| ODS Properties Limited | Administrative & support | 2003 |
| OES Consulting Civils Limited | Construction | 2022 |
| OES Consulting Limited | Professional & scientific | 2017 |
| Office Cabin Experts Limited | Construction | 2025 |
| Office Options (Midlands) Limited | Manufacturing | 1993 |
| Offsite Engineering Solutions Ltd | Manufacturing | 2018 |
| Offspring International Limited | Wholesale & retail | 1991 |
| Offspring International Trustees Limited | Administrative & support | 2023 |
| OH Flopping Fiddlesticks Limited | Wholesale & retail | 2019 |
| OH My Cod’N’Chips Limited | Hospitality | 2025 |
| OJ Industries Ltd | Wholesale & retail | 2022 |
| Olabis Group Global Ltd | Wholesale & retail | 2026 |
| Oladoc Limited | Health & social care | 2021 |
| Ola’S Fadez Ltd | Other services | 2026 |
| Old College House Management Limited | Hospitality | 1990 |
| Old Gold Pack Ltd | Wholesale & retail | 2026 |
| Oldbury PUB Company Ltd | Hospitality | 2023 |
| Oldbury Tyre Ltd | Wholesale & retail | 2024 |
| Oliver Graham Holdings Ltd | Financial services | 2024 |
| Oliver's Indian Limited | Hospitality | 2018 |
| Olivtrans Limited | Transport & logistics | 2021 |
| OM Real Estate and Build Ltd | Construction | 2024 |
| OM Shanti Trading Limited | Wholesale & retail | 2011 |
| Omertà Jewellers Ltd | Wholesale & retail | 2026 |
| Omnis One FM Limited | Construction | 2025 |
| OMO Barber Ltd | Other services | 2025 |
| On-The-Go Lodging Ltd | Real estate | 2023 |
| ONBOARD4ME Limited | Other services | 2021 |
| Oncall Welding Group Ltd | Manufacturing | 2026 |
| One 4 YOU Services Limited | Transport & logistics | 2006 |
| One Consultant Ltd | Information & communication | 2025 |
| One Point Courier Ltd | Transport & logistics | 2017 |
| One Stop Commercials Ltd | Wholesale & retail | 2021 |
| One Stop Kitchens Ltd | Manufacturing | 2012 |
| One Stop Marketing Hub Limited | Professional & scientific | 2022 |
| One Weigh (UK) Ltd | Manufacturing | 2014 |
| Online Amaseller Ltd | Wholesale & retail | 2020 |
| Online Windows and Doors Ltd | Construction | 2015 |
| Only Brush Away Ltd | Construction | 2026 |
| Opal General Cleaning & Home Services Ltd | Administrative & support | 2025 |
| Opaluxestays Limited | Real estate | 2026 |
| Ophili Drylining Ltd | Construction | 2025 |
| Optiliving Ltd | Health & social care | 2024 |
| Optimised Sport Ltd | Information & communication | 2023 |
| Optimo Electrical Services Ltd | Construction | 2023 |
| Optimo Property Services Ltd | Construction | 2022 |
| Optimum Engineered Solutions Ltd | Other services | 2010 |
| Optimus Estate Planning Limited | Professional & scientific | 2021 |
| Optimus Time Limited | Financial services | 2021 |
| Opus New Horizons Ltd | Wholesale & retail | 2013 |
| Oracle Housing C.I.C. | Real estate | 2022 |
| Orchard Leisure at Holt Ltd | Hospitality | 2016 |
| Orchards Procurement Services Limited | Professional & scientific | 2024 |
| Orchid JET J G. Shepherd Limited | Wholesale & retail | 2003 |
| Orhaan Ltd | Wholesale & retail | 2025 |
| Oriental Bridge Ltd | Hospitality | 2026 |
| Origin Engineering Solutions Ltd | Information & communication | 2021 |
| Ormixfoods Ltd | Hospitality | 2023 |
| Orovia Ventures Ltd | Wholesale & retail | 2025 |
| Orrexian Ltd | Hospitality | 2021 |
| Orty Carpentry and Building Ltd | Manufacturing | 2025 |
| Osagie Investment Properties Ltd | Real estate | 2025 |
| Oscabel Ltd | Wholesale & retail | 2026 |
| Oscaws Limited | Administrative & support | 2005 |
| OSP Engines Limited | Manufacturing | 2002 |
| Otimo Sports Ltd | Wholesale & retail | 2025 |
| Otos Engineering Solutions Ltd | Professional & scientific | 2026 |
| OUR Digital School Limited | Education | 2025 |
| OUR Keys Ltd | Extraterritorial | 2023 |
| OUR Keys Property Services Ltd | Wholesale & retail | 2018 |
| Overcomer Heritage Limited | Real estate | 2025 |
| Overseas Buyer Ltd | Construction | 2025 |
| Owens & Tullett Properties Limited | Real estate | 2023 |
| Owens Hvac Ltd | Construction | 2024 |
| OWR Associates Limited | Health & social care | 2015 |
| P & E Plant Hire Limited | Construction | 2026 |
| P & R Edmunds (Holdings) Limited | Construction | 2016 |