| Oana Professional Cleaning Services Ltd | Administrative & support | 2019 |
| Oanceaslaw Ltd | Transport & logistics | 2026 |
| OAO Property Ltd | Real estate | 2016 |
| Oarsome Limited | Information & communication | 2007 |
| Oasis Business Personnel Ltd | Administrative & support | 2024 |
| Oasis Haven Properties Limited | Real estate | 2025 |
| Oasis Live Ltd | Wholesale & retail | 2020 |
| Oasis Logistics & Storage Ltd | Professional & scientific | 2024 |
| Oasis Outlet Ltd | Wholesale & retail | 2026 |
| Oate 2006 Ltd | Administrative & support | 2014 |
| OB Property Developments Limited | Extraterritorial | 2023 |
| OBA Care Services Ltd | Administrative & support | 2023 |
| OBA! Brazilian Food Ltd | Hospitality | 2018 |
| Obehimen Ltd | Professional & scientific | 2023 |
| Obelisk Construction Limited | Construction | 2008 |
| Obelisk Couriers Limited | Transport & logistics | 2006 |
| Obelisk Spinney Pocket Park Community Interest Company | Arts & recreation | 2007 |
| OBI 1AND2 Limited | Health & social care | 2016 |
| Obisonic UK Limited | Other services | 2014 |
| Objects of Care Limited | Wholesale & retail | 2022 |
| Oblique Events Ltd | Hospitality | 2018 |
| Oblique Hospitality Ltd | Hospitality | 2025 |
| Obms Holdings Ltd | Real estate | 2015 |
| Obox Consulting Ltd | Professional & scientific | 2020 |
| Obscure-Works Ltd | Information & communication | 2023 |
| Obsidian Shift Limited | Information & communication | 2024 |
| Obtainwise Limited | Wholesale & retail | 1992 |
| Ocbl Care Ltd | Health & social care | 2009 |
| Occhio Lighting UK Ltd | Wholesale & retail | 2022 |
| Ocean Bites Ltd | Hospitality | 2023 |
| Ocean Dynamics Limited | Professional & scientific | 2023 |
| Ocean Rise (Croyde) Management Company Limited | Real estate | 2018 |
| Ocean View Services Ltd | Administrative & support | 2020 |
| Ocee Design Limited | Manufacturing | 1990 |
| Ocee International Ltd | Manufacturing | 2016 |
| Ochl Care Ltd | Financial services | 2010 |
| Ochu Ltd | Wholesale & retail | 2025 |
| Ocicat Limited | Professional & scientific | 2025 |
| Ocir Limited | Education | 2019 |
| Ocir Support CIC | Education | 2023 |
| Ocise CIC | Information & communication | 2025 |
| OCM CR Wealth Management Limited | Financial services | 2017 |
| OCM Employee Benefits Limited | Professional & scientific | 2019 |
| OCM Wealth Management Holding Company Limited | Financial services | 2020 |
| OCM Wealth Management Limited | Financial services | 2004 |
| Ocoda Consult Limited | Health & social care | 2023 |
| OCS Paint Limited | Wholesale & retail | 2016 |
| Octare Limited | Professional & scientific | 2020 |
| Octopus Audio Visual Ltd | Information & communication | 2020 |
| Ocular Vision Ltd | Professional & scientific | 2013 |
| Oculoplastica Limited | Health & social care | 2024 |
| Ocza Ltd | Other services | 2018 |
| ODD Socks Creative Ltd | Professional & scientific | 2023 |
| Oddball Entertainment Limited | Information & communication | 2008 |
| Odge Media Ltd | Professional & scientific | 2023 |
| ODH Cundill Limited | Education | 2024 |
| Odon Mensah Limited | Health & social care | 2013 |
| Odyssey Transport Solutions Ltd | Transport & logistics | 2024 |
| OE PUB Ltd | Hospitality | 2025 |
| OE4GROWTH Limited | Professional & scientific | 2024 |
| Oefes Ltd | Hospitality | 2024 |
| OEM Car Parts Ltd | Wholesale & retail | 2018 |
| OF Logistics Ltd | Transport & logistics | 2026 |
| OFF Grid Properties Ltd | Real estate | 2026 |
| OFF the Wall Properties Limited | Real estate | 2020 |
| OFF the Wall Property Ltd | Real estate | 2020 |
| Offbeet (Fareham) Limited | Hospitality | 2017 |
| Offer Express Ltd | Education | 2020 |
| Office Curator Limited | Professional & scientific | 2018 |
| Office Furniture Box Ltd | Extraterritorial | 2023 |
| Offsite Engineered Products UK Ltd | Manufacturing | 2019 |
| Offsite Logistics Limited | Extraterritorial | 2014 |
| Offthebreeze Ltd | Construction | 2020 |
| OG Comms Ltd | Information & communication | 2022 |
| OG Esports Limited | Professional & scientific | 2025 |
| Ogdent Limited | Wholesale & retail | 2011 |
| Ogeaku Services Ltd | Professional & scientific | 2022 |
| Oggi Doggy Edutainment Limited | Extraterritorial | 2015 |
| Ogwell Developments Ltd | Construction | 2015 |
| OH Mentoring Ltd | Education | 2025 |
| Ohana Consultancy Ltd | Professional & scientific | 2018 |
| OHB Holdings Ltd | Professional & scientific | 2022 |
| Ohmy Media Ltd | Professional & scientific | 2024 |
| Oikos Residential Agent Ltd | Real estate | 2025 |
| Oilsense Limited | Administrative & support | 2004 |
| OJ Management Solutions Ltd | Information & communication | 2010 |
| Ojan Healthcare Limited | Health & social care | 2020 |
| OJM Property Ltd | Real estate | 2024 |
| OJM Trans Ltd | Transport & logistics | 2024 |
| OJM Vehicle Sales Ltd | Wholesale & retail | 2025 |
| Okeanika Limited | Construction | 2025 |
| Okert Enterprise Ltd | Transport & logistics | 2020 |
| Okissi Unique Hairkraft Ltd | Other services | 2025 |
| Okka Limited | Wholesale & retail | 2025 |
| Okoeguale-Ebhodaghe and Sons Ltd | Health & social care | 2026 |
| Okoh D Ltd | Public administration | 2023 |
| Okoye Properties Limited | Real estate | 2019 |
| Oktik Software Limited | Information & communication | 2020 |
| Oktik Technology Limited | Professional & scientific | 2015 |
| OL Instalations Ltd | Construction | 2014 |