| Ottaway Finance Services Limited | Professional & scientific | 2025 |
| Otter Drive (Carshalton) RTM Company Limited | Real estate | 2019 |
| Otter Medical Services Ltd | Wholesale & retail | 2025 |
| Otter Produces Limited | Arts & recreation | 2023 |
| Otter Vets Ltd | Extraterritorial | 2018 |
| Otteray Limited | Households | 1989 |
| Otters Brook Management Company (Cannington) Limited | Real estate | 2017 |
| Otters Offers Ltd | Wholesale & retail | 2025 |
| Otterwood Associates Ltd | Real estate | 2025 |
| Ottilie Group Limited | Other services | 2023 |
| Otto Chen Associates Limited | Construction | 2022 |
| Otto Logistics Ltd | Transport & logistics | 2022 |
| Otto's Garage Limited | Wholesale & retail | 2022 |
| Ottobry Ltd | Real estate | 2020 |
| Ottonline Limited | Wholesale & retail | 2023 |
| Ouarray Ltd | Wholesale & retail | 2023 |
| Oughton Leisure Products Limited | Extraterritorial | 1984 |
| OUR Footprints Ltd | Construction | 2017 |
| OUR Footprints Trustee Limited | Extraterritorial | 2025 |
| OUR Haven Community CIC | Education | 2025 |
| OUR Home Ltd | Real estate | 2011 |
| OUR Honest Foods Ltd | Hospitality | 2013 |
| OUR Media (2023) Limited Partnership | | 2005 |
| OUR Media Holdings Ltd | Financial services | 2021 |
| OUR Media Limited | Information & communication | 2006 |
| OUR Story 25 Limited | Information & communication | 2023 |
| Ouroboros I T Limited | Information & communication | 2017 |
| Ourpatch CIC | Manufacturing | 2026 |
| Ourstories Limited | Wholesale & retail | 2022 |
| OUT Beyond Limited | Other services | 2022 |
| OUT of Hand Limited | Manufacturing | 1997 |
| OUT of School Club @Hanham Abbots Ltd | Health & social care | 2013 |
| OUT of Squire Ltd | Construction | 2025 |
| OUT of Step Ltd | Wholesale & retail | 2006 |
| OUT of the Woodwork Ltd. | Manufacturing | 2015 |
| OUT the Box Thinking Limited | Professional & scientific | 2023 |
| OUT There Forest School and Kindergarten Ltd | Education | 2017 |
| OUT There Indoors Ltd | Education | 2022 |
| OUT There Kids Club Limited | Arts & recreation | 2015 |
| Out-House Consulting Limited | Professional & scientific | 2013 |
| Outcomes Change Advisory Limited | Professional & scientific | 2026 |
| Outcraft Studio Ltd | Information & communication | 2024 |
| Outdoor Active Limited | Wholesale & retail | 2000 |
| Outlaw Collective Ltd | Other services | 2018 |
| Outlaw Limited | Extraterritorial | 2018 |
| Outlaw Music Limited | Information & communication | 1979 |
| Outlet Trade Frames Limited | Wholesale & retail | 2017 |
| Outpace Imports Limited | Wholesale & retail | 2021 |
| Outpace Logistics Limited | Transport & logistics | 2013 |
| Outrate Data Limited | Information & communication | 2025 |
| Outsales Limited | Professional & scientific | 2015 |
| Outshine Telephone Training & Resources Ltd | Other services | 2018 |
| Outsource UK Limited | Administrative & support | 1991 |
| Outstanding Services Ltd | Hospitality | 2021 |
| Outurn Limited | Households | 1982 |
| Outvisit Limited | Information & communication | 2015 |
| Oval (2321) Limited | Wholesale & retail | 2026 |
| Oval (787) Limited | Professional & scientific | 1969 |
| Oval Holdco Ltd | Information & communication | 2017 |
| Oval Nominees Limited | Extraterritorial | 1984 |
| Oval Subsidiary 1 Limited | Professional & scientific | 2012 |
| Ovalb Ltd | Information & communication | 2022 |
| Ovalsec Limited | Extraterritorial | 1978 |
| Ovation Finance Limited | Financial services | 1999 |
| Ovation Finance Trustee Limited | Professional & scientific | 2018 |
| Over 60'S Tea Room (Thornbury) CIC | Hospitality | 2021 |
| Over Court Mews Management Limited | Households | 1985 |
| Over the City Ltd | Transport & logistics | 2024 |
| Over the Edge Rope Access & Safety Netting Ltd | Construction | 2015 |
| Overbeep Ltd | Financial services | 2019 |
| Overflow PUB Co Ltd | Wholesale & retail | 2023 |
| Overhill Property Limited | Real estate | 2017 |
| Overkill-Systems Limited | Other services | 2004 |
| Overmyst Consultancy Limited | Professional & scientific | 2023 |
| Overnhill Court (NO. 2) Limited | Households | 1970 |
| Overnhill Court (NO. 4) Limited | Households | 1970 |
| Overnhill Court (NO. 5) Limited | Households | 1970 |
| Overnhill Court NO.3 (2000) Limited | Households | 2000 |
| Overnhill Properties Ltd | Real estate | 2025 |
| Overnhurst Court Management (Downend) Limited | Households | 1980 |
| Oversea Guardian Limited | Administrative & support | 2021 |
| Overseas Entity Registrations Limited | Professional & scientific | 2022 |
| Overseas Property Centres Limited | Real estate | 1999 |
| Overside Planning Consultancy Limited | Construction | 2014 |
| Overstones Plastering Ltd | Construction | 2024 |
| Oveza Limited | Administrative & support | 2015 |
| Oviedo LP | | 2011 |
| Ovies Properties Ltd | Real estate | 2022 |
| Ovifumi Transport Ltd | Transport & logistics | 2019 |
| Ovilex Prest Ltd | Transport & logistics | 2025 |
| Ovis Store Ltd | Wholesale & retail | 2025 |
| OVY & Nathan Limited | Construction | 2014 |
| OW Holdco Limited | Financial services | 2025 |
| Ow-Ansah Ltd | Administrative & support | 2025 |
| OWB Coaching Ltd | Other services | 2022 |
| Owen Cogan Psychology Ltd | Professional & scientific | 2025 |
| Owen IT Ltd | Information & communication | 2019 |
| Owen Lord Ltd | Professional & scientific | 2025 |
| Owen O'Keeffe Ltd | Other services | 2021 |
| Owen Philip Editing Ltd | Information & communication | 2021 |