| Orange River Capital Limited | Agriculture & fishing | 2020 |
| Orange River Limited | Information & communication | 2003 |
| Orange Rock Group Ltd | Professional & scientific | 2016 |
| Orange Scaffolding Limited | Arts & recreation | 1987 |
| Orange Stone Construction Limited | Construction | 2024 |
| Orange Supplies Limited | Professional & scientific | 1995 |
| Orangebox Group Limited | Manufacturing | 2000 |
| Orangebox Limited | Manufacturing | 1997 |
| Orantec Limited | Information & communication | 2008 |
| Orantor | Professional & scientific | 2025 |
| Orascom African Developing Company Ltd | Construction | 2025 |
| Orascom African Medical Company Ltd | Wholesale & retail | 2025 |
| Orawi Ltd | Real estate | 2018 |
| Orbicart Limited | Wholesale & retail | 2025 |
| Orbis Care Services Ltd | Health & social care | 2024 |
| Orbis Education and Care Bidco Limited | Health & social care | 2016 |
| Orbis Education and Care Finco Limited | Health & social care | 2016 |
| Orbis Education and Care Limited | Health & social care | 2005 |
| Orbis Education and Care Midco Limited | Health & social care | 2016 |
| Orbis Education and Care Services Limited | Professional & scientific | 2014 |
| Orbis Education and Care Topco Limited | Health & social care | 2016 |
| Orbis ESG Technologies Limited | Information & communication | 2024 |
| Orbit AI Software Limited | Information & communication | 2026 |
| Orbit EPS Ltd | Manufacturing | 2023 |
| Orbit Industries PC | | 2018 |
| Orbit Theatre Limited | Arts & recreation | 1969 |
| Orbital Grade Entertainment Ltd | Information & communication | 2026 |
| Orbital Resourcing Ltd | Administrative & support | 2016 |
| Orbitel Communications Limited | Information & communication | 2021 |
| Orbitline Ltd | Information & communication | 2025 |
| Orbix Energy Ltd | Construction | 2025 |
| Orbtel Limited | Manufacturing | 1997 |
| Orbyt Skin Limited | Wholesale & retail | 2020 |
| Orca Technologies Limited | Wholesale & retail | 2021 |
| Orchard Automotive Cardiff Ltd | Wholesale & retail | 2026 |
| Orchard Court (Lisvane) Management Limited | Real estate | 1985 |
| Orchard Davies Limited | Professional & scientific | 2014 |
| Orchard Grove Medical Services Limited | Health & social care | 2018 |
| Orchard Hold Ltd | Real estate | 2025 |
| Orchard Keys Ltd | Real estate | 2025 |
| Orchard Media and Events EOT Trustee Limited | Professional & scientific | 2024 |
| Orchard Media and Events Group Investments Ltd | Administrative & support | 2021 |
| Orchard of Life Film Ltd | Information & communication | 2015 |
| Orchard Property Development Management Limited | Professional & scientific | 2016 |
| Orchard Valley Contractors Ltd | Construction | 2024 |
| Orchards Construction Limited | Administrative & support | 2011 |
| Orchards Estates Whitchurch Ltd | Real estate | 2016 |
| Orchid Corporation PC | | 2017 |
| Orchid Fragrant Ltd | Wholesale & retail | 2025 |
| Orchid Global Services UK Ltd | Administrative & support | 2019 |
| Orchid Lane Limited | Arts & recreation | 2013 |
| ORD Landscapes & Driveways Ltd | Construction | 2026 |
| Orddu Energy Park Limited | Energy | 2023 |
| Order Foodie Limited | Other services | 2019 |
| Order of ST. John Priory for Wales Trustee Corporation Limited | Extraterritorial | 1994 |
| Orderzen Ltd | Other services | 2025 |
| Ordinal Numerology Ltd | Wholesale & retail | 2025 |
| Ordinate Consulting Ltd | Information & communication | 2025 |
| Ordis UK Limited | Information & communication | 2026 |
| Ordo Courier Services Limited | Construction | 2011 |
| Ordo Design & Build Ltd | Professional & scientific | 2026 |
| Ordo Healthcare Ltd | Health & social care | 2021 |
| ORE Innovations Limited | Professional & scientific | 2025 |
| Oreeas Services Ltd | Wholesale & retail | 2021 |
| Orefia Services Ltd | Administrative & support | 2020 |
| Oren Anna Ltd | Households | 2021 |
| Oren Retreats Limited | Other services | 2026 |
| Oren Wellness Limited | Arts & recreation | 2024 |
| Oreno Limited | Hospitality | 2019 |
| Organic Fruits Limited | Wholesale & retail | 2018 |
| Organic House Natural Products to Supply Cosmetics Ltd | Wholesale & retail | 2024 |
| Organic LAB UK Ltd | Wholesale & retail | 2018 |
| Organic Landscape Garden Designaire Ltd | Administrative & support | 2023 |
| Organic Natural Sources Ltd | Health & social care | 2022 |
| Organic Nutrition Limited | Wholesale & retail | 2002 |
| Organic Sales Ltd | Information & communication | 2025 |
| Organicafe Limited | Hospitality | 2016 |
| Organika Holding Ltd | Financial services | 2021 |
| Orgueil Limited | Financial services | 2014 |
| ORH Developments Ltd | Construction | 2019 |
| Orhan Nerkiz Ltd | Wholesale & retail | 2022 |
| Oriana Solutions Ltd | Wholesale & retail | 2018 |
| Oriel Design Limited | Professional & scientific | 2003 |
| Oriel House RTM Company Ltd | Households | 2016 |
| Oriel's Modern Meat Shop Limited | Wholesale & retail | 2020 |
| Oriemac Machinery Vehicle Co., Ltd | Extraterritorial | 2015 |
| Oriental Enterprise Southampthon Limited | Wholesale & retail | 2024 |
| Oriental Expo Limited | Professional & scientific | 2015 |
| Oriental Express (Cardiff) Ltd. | Hospitality | 2014 |
| Oriental Potential Co., Ltd. | Financial services | 2021 |
| Oriental Vibe Limited | Wholesale & retail | 2025 |
| Oriental Watch Co., Ltd | Wholesale & retail | 2021 |
| Orients Hub Limited | Wholesale & retail | 2025 |
| Origami Gold Ltd | Professional & scientific | 2018 |
| Origin Project Performance Ltd | Health & social care | 2021 |
| Origin Trade Private Limited | Manufacturing | 2026 |
| Origin Vets Clinic Ltd | Professional & scientific | 2020 |
| Origin-Blinds Ltd | Manufacturing | 2017 |
| Origin-Climbing Ltd | Manufacturing | 2020 |
| Original CAD Plans Ltd | Professional & scientific | 2024 |