| Olive Network Ltd | Administrative & support | 2023 |
| Olive Radiant Services Ltd | Information & communication | 2019 |
| Olive Support Ltd | Professional & scientific | 2025 |
| Olive Venture Properties Ltd | Real estate | 2024 |
| Olive Wheel Management Company Limited | Households | 2019 |
| Oliver Baker Electrical Limited | Construction | 2023 |
| Oliver Cassell Design Ltd | Professional & scientific | 2026 |
| Oliver King Consulting Limited | Administrative & support | 2020 |
| Oliver Petroleum Ltd. | Wholesale & retail | 2010 |
| Oliver Quinn Limited | Professional & scientific | 2017 |
| Oliver Wild Ltd | Construction | 2011 |
| Oliver Wilson Limited | Manufacturing | 2017 |
| Oliver's Bar and Restaurant Ltd | Hospitality | 2017 |
| Olivers Funeral Services Limited | Other services | 2016 |
| Olives Property Ltd | Real estate | 2024 |
| Olivia Clare Limited | Administrative & support | 2015 |
| Olivia Kate Ltd | Information & communication | 2025 |
| Olivia Rose Consulting Ltd | Professional & scientific | 2023 |
| Olivias Emporium Ltd | Wholesale & retail | 2022 |
| Olivias Trains Ltd | Wholesale & retail | 2018 |
| Ollcrom Limited | Real estate | 2025 |
| Olly Moss Limited | Arts & recreation | 2013 |
| Olmec Advanced Materials Limited | Manufacturing | 1990 |
| OLO Robotics Ltd | Information & communication | 2020 |
| Olsen Custom Bicycles Limited | Manufacturing | 2013 |
| Olson and Baker Ltd. | Wholesale & retail | 2015 |
| Oluwasegun Adeosun & Co Ltd | Other services | 2023 |
| Olympia Furniture Ltd | Wholesale & retail | 2026 |
| Olympia Wellbeing Academy CIC | Public administration | 2019 |
| Olympic Compactor Rentals (UK) Limited | Manufacturing | 1983 |
| Olympos Electrics Limited | Construction | 2022 |
| Olympus Cleaning Services Limited | Administrative & support | 2019 |
| Olympus JIU Jitsu Ltd | Arts & recreation | 2022 |
| OM & Co PVT Limited | Administrative & support | 2024 |
| OM Property Ventures Limited | Real estate | 2021 |
| Omall Ltd | Other services | 2025 |
| Omar Recycling Shop Ltd | Wholesale & retail | 2019 |
| Omaraco Ltd | Wholesale & retail | 2020 |
| Omari Williams Management Services Ltd | Administrative & support | 2011 |
| Omars Estera Ltd | Wholesale & retail | 2026 |
| Ombra Lighting Ltd | Wholesale & retail | 2021 |
| OMD Projects Ltd | Information & communication | 2015 |
| OME Sweet OME Limited | Real estate | 2012 |
| Omega Comms Ltd | Information & communication | 2025 |
| Omega Court Management Company Limited | Households | 1988 |
| Omega Extra Foods Ltd | Wholesale & retail | 2026 |
| Omega Foodstore Ltd | Wholesale & retail | 2012 |
| Omega Luxury Giveaways Limited | Extraterritorial | 2022 |
| Omega Properties UK Ltd | Real estate | 2006 |
| Omega Works Ltd | Professional & scientific | 2023 |
| Omer's Trading Limited | Wholesale & retail | 2026 |
| OMG 888 Property Services Limited | Real estate | 2019 |
| OMH Hold Co Ltd | Professional & scientific | 2026 |
| OMH Prop Co Group Ltd | Real estate | 2024 |
| OMJ Signature Clean Ltd | Administrative & support | 2026 |
| OML Media Ltd | Professional & scientific | 2017 |
| OML Trading Limited | Wholesale & retail | 2014 |
| Omletec Ltd | Information & communication | 2019 |
| Omni Parcel Ltd | Other services | 2025 |
| Omni-Tech Electronics Limited | Manufacturing | 2008 |
| Omnia Estates Limited | Real estate | 2007 |
| Omnia Offices Limited | Real estate | 2004 |
| Omnia Personnel Services Limited | Administrative & support | 2015 |
| Omnia Property Group Limited | Extraterritorial | 2018 |
| Omnia Team Ltd | Information & communication | 2022 |
| Omnico (Developments) Limited | Extraterritorial | 1962 |
| Omnico Plastics Limited | Extraterritorial | 1996 |
| Omnidynamic Group Limited | Financial services | 2023 |
| Omniflux Ltd | Administrative & support | 2025 |
| Omnis Data Limited | Information & communication | 2015 |
| Omnis Media Limited | Information & communication | 2011 |
| Omnitrix General Trading Ltd | Wholesale & retail | 2025 |
| Omnium Consulting Limited | Professional & scientific | 2010 |
| Omodoo Ltd | Other services | 2017 |
| Omos Solutions Ltd | Health & social care | 2026 |
| Omsales Ltd | Wholesale & retail | 2025 |
| OMT Consultants Ltd | Professional & scientific | 2021 |
| OMT Haulage Ltd | Transport & logistics | 2022 |
| OMY Cleaning Ltd | Administrative & support | 2024 |
| ON Broadway Dance Fitness Ltd | Professional & scientific | 2024 |
| ON Fire Inc Ltd | Wholesale & retail | 2019 |
| ON Plan Real Estate Ltd | Real estate | 2025 |
| ON Point Civils and Building Services Ltd | Construction | 2025 |
| ON Point Leadership Ltd | Professional & scientific | 2019 |
| ON the Ball (OTB) Ltd | Wholesale & retail | 2025 |
| ON the Brink Cohousing Community Limited | Hospitality | 2015 |
| ON the Move Play, Sport and Physical Activity Limited | Arts & recreation | 2017 |
| ON the Spot Tyres Ltd | Wholesale & retail | 2021 |
| ON Top Food Limited | Hospitality | 2025 |
| ON Track Flooring Limited | Wholesale & retail | 2004 |
| On-Power Electrical and Plumbing Ltd | Construction | 2015 |
| Onboard Skatepark Sheffield Ltd. | Arts & recreation | 2013 |
| Once Upon a Time Daycare Limited | Education | 2017 |
| Once Upon a Time Dronfield Limited | Health & social care | 2021 |
| Once Upon a Time Nursery Limited | Education | 2011 |
| Once Upon a Time Play Limited | Arts & recreation | 2017 |
| One Acre Web Limited | Information & communication | 2026 |
| One Ambition Ltd | Hospitality | 2021 |
| One Beat PR Limited | Information & communication | 2017 |
| One Body Athletic Ltd | Arts & recreation | 2017 |