| Oleg Sencha Ltd | Professional & scientific | 2025 |
| Oleka Consulting Ltd | Professional & scientific | 2015 |
| Oleperu Limited | Information & communication | 2013 |
| Olital Solutions Limited | Other services | 2024 |
| Olive Collective CIC | Education | 2023 |
| Olive Square Pmar Ltd | Construction | 2018 |
| Olive Tree Bar and Restaurants Ltd | Hospitality | 2025 |
| Olive Tree Capital Ltd | Real estate | 2026 |
| Olive Tree Mezze Ltd | Hospitality | 2026 |
| Olive Tree Milton Keynes Ltd | Hospitality | 2024 |
| Oliver Anderson Ltd | Construction | 2023 |
| Oliver Anderson Properties Ltd | Real estate | 2024 |
| Oliver Calcutt Architectural Design Limited | Professional & scientific | 2015 |
| Oliver Folkard Ltd | Professional & scientific | 2026 |
| Oliver Gray Ltd | Wholesale & retail | 2021 |
| Oliver H Homes Ltd | Real estate | 2025 |
| Oliver J Elliot Limited | Wholesale & retail | 2025 |
| Oliver Jane Limited | Manufacturing | 2016 |
| Oliver Medi Services Ltd | Health & social care | 2022 |
| Oliver Patrick Media Ltd | Professional & scientific | 2024 |
| Olives Estates Limited | Real estate | 2025 |
| Olive’S Enterprises Ltd | Wholesale & retail | 2020 |
| Olivia & Rosie Properties Limited | Real estate | 2021 |
| Oliwell Holdings Limited | Administrative & support | 2025 |
| OLL (Cranfield) Limited | Construction | 2020 |
| Ollak Limited | Transport & logistics | 2016 |
| Olley & Guise Bespoke Joinery Limited | Construction | 2017 |
| Olli Investments Ltd | Real estate | 2020 |
| Olmar Trading Ltd | Wholesale & retail | 2024 |
| Olney Executive Travel Ltd | Transport & logistics | 2020 |
| Olney Kitchens Limited | Manufacturing | 2010 |
| Olney Padel Club Limited | Arts & recreation | 2025 |
| Olorium Limited | Wholesale & retail | 2025 |
| Oloweh Ohuyedin (OO) Ltd | Wholesale & retail | 2026 |
| Olumba Services Ltd | Hospitality | 2024 |
| OLY Executive Ltd | Transport & logistics | 2019 |
| Olyi Ltd | Information & communication | 2014 |
| Olympus Gecko Sales Ltd | Wholesale & retail | 2022 |
| Olyv Limited | Professional & scientific | 2024 |
| OM Estates Limited | Real estate | 2003 |
| OM Home Care Ltd | Health & social care | 2025 |
| OM Namah Shivay Limited | Health & social care | 2023 |
| OM Recruitment Services Ltd | Construction | 2022 |
| OMA KAT Ltd | Other services | 2015 |
| Omanyeaba Ltd | Wholesale & retail | 2023 |
| Omar Auto Repairs Garage Limited | Wholesale & retail | 2024 |
| Omega 30 Limited | Professional & scientific | 2025 |
| Omega GT Ltd | Hospitality | 2025 |
| Omega Move Services Ltd | Health & social care | 2019 |
| Omega N.S. Ltd | Information & communication | 2024 |
| Omega OM Ltd | Information & communication | 2026 |
| Omegasun Ltd | Construction | 2017 |
| OMI Griva MK Limited | Transport & logistics | 2021 |
| OMI Griva UK Limited | Households | 2022 |
| Omisa Holdings Ltd | Financial services | 2025 |
| Omisa Investments Ltd | Real estate | 2025 |
| Omisa Ltd | Professional & scientific | 2022 |
| OMN Ltd | Public administration | 2020 |
| Omne Yoga Ltd | Education | 2024 |
| Omni Accounting Services Ltd | Professional & scientific | 2018 |
| Omni Source Alliance Ltd | Professional & scientific | 2024 |
| Omnia Support Services Ltd | Professional & scientific | 2015 |
| Omnia Technical Plastics Ltd | Manufacturing | 2010 |
| Omniaa Ltd | Wholesale & retail | 2019 |
| Omnibrick Ltd | Construction | 2023 |
| Omoasam Limited | Administrative & support | 2025 |
| OMQ Consulting Ltd | Professional & scientific | 2013 |
| Omron Electronics Limited | Wholesale & retail | 1991 |
| Omron Healthcare UK Limited | Wholesale & retail | 1990 |
| OMT Barber Ltd | Other services | 2017 |
| Omyra Limited | Professional & scientific | 2007 |
| ON CAP Limited | Financial services | 2025 |
| ON Demand Records Limited | Information & communication | 2021 |
| ON on Dumpling Ltd | Hospitality | 2026 |
| ON Point Pubs Limited | Administrative & support | 2023 |
| ON Point Roofing & Building Ltd | Construction | 2025 |
| ON Road Training Ltd | Education | 2025 |
| ON Site Coatings Ltd | Construction | 2023 |
| ON Site Spraying Services Ltd | Construction | 2025 |
| ON the MAP (UK) Limited | Extraterritorial | 2018 |
| ON the Mark Consulting Limited | Professional & scientific | 2018 |
| Onar Properties Ltd | Information & communication | 2013 |
| Oncall (GB) Limited | Administrative & support | 2014 |
| Ondemandsolutions Consultancy Ltd | Information & communication | 2009 |
| One Apex Ltd | Transport & logistics | 2026 |
| One Bite at a Time Limited | Professional & scientific | 1990 |
| One Call Installations Limited | Construction | 2016 |
| One Diverse Limited | Professional & scientific | 2025 |
| One Eternal Ltd | Wholesale & retail | 2023 |
| One Generation Limited | Wholesale & retail | 2020 |
| One Good Reason Ltd | Professional & scientific | 2023 |
| One MAN Chop Limited | Information & communication | 2016 |
| One Nine Squared Limited | Financial services | 2025 |
| One SRI Lanka Limited | Extraterritorial | 2024 |
| One Summer Day Ltd | Wholesale & retail | 2025 |
| One Touch Heating Solutions Ltd | Construction | 2024 |
| One-Cloud Europe Limited | Information & communication | 2013 |
| Onecab Limited | Transport & logistics | 2025 |
| Onecote Honeysuckle Limited | Extraterritorial | 2023 |
| Onehazara Ltd | Information & communication | 2025 |