| Orchard Homes Construction Limited | Construction | 2019 |
| Orchard Homes Limited | Construction | 2018 |
| Orchard Plant Hire Ltd | Administrative & support | 2022 |
| Orchard Toys Limited | Manufacturing | 1979 |
| Orchards Homes Limited | Real estate | 2015 |
| Orchestrateuk Ltd. | Information & communication | 2012 |
| Orchid Management Services Limited | Real estate | 2019 |
| Orchid Organisational Development Limited | Professional & scientific | 1999 |
| Orchid Properties Limited | Real estate | 2001 |
| Orchid Property Partners Ltd | Households | 2025 |
| Ordo Ltd | Professional & scientific | 2025 |
| Orelle Consulting Limited | Professional & scientific | 2021 |
| Organic Industries UK Ltd | Wholesale & retail | 2024 |
| Organic Natural Cosmetics Contract Manufacturing Ltd | Manufacturing | 2026 |
| Organised FUN Consultancy Ltd | Professional & scientific | 2022 |
| Organised Ideas Limited | Administrative & support | 2014 |
| Orhicle Events Ltd | Hospitality | 2020 |
| Oriah Haus Limited | Other services | 2025 |
| Oriah Holdings Ltd | Real estate | 2022 |
| Oriel Management Company Limited | Households | 2022 |
| Oriental Business International Limited | Wholesale & retail | 2026 |
| Oriental Express Nottingham Ltd | Hospitality | 2025 |
| Oriental Finds and Artistry Ltd | Wholesale & retail | 2025 |
| Oriental Foods Distributor Ltd | Wholesale & retail | 2021 |
| Oriental Healthcare Centre Ltd | Other services | 2025 |
| Oriental Mart Ltd | Extraterritorial | 2012 |
| Orientalmart (UK) Limited | Wholesale & retail | 2007 |
| Orientalmart Properties Ltd | Real estate | 2019 |
| Oriente Ltd | Real estate | 2025 |
| Origin FX Ltd | Arts & recreation | 2026 |
| Origin Kitchen Ltd. | Manufacturing | 2019 |
| Origin Studios Ltd | Wholesale & retail | 2020 |
| Original Movement Community Ltd | Education | 2022 |
| Original Movement Ltd | Arts & recreation | 2012 |
| Original Papas Grill Limited | Hospitality | 2024 |
| Original Wood Tops Limited | Manufacturing | 2013 |
| Origins Group Holdings Ltd | Financial services | 2023 |
| Oriko Studios Ltd | Information & communication | 2022 |
| Orina Group Limited | Financial services | 2017 |
| Orinti Ltd | Professional & scientific | 2025 |
| Orion Accountants Limited | Professional & scientific | 2011 |
| Orion Dusk Limited | Administrative & support | 2025 |
| Orion IT Consulting Limited | Information & communication | 2004 |
| Orion Recursive Intelligent Optimisation Nexus Limited | Information & communication | 2026 |
| Orion Shopping Ltd | Professional & scientific | 2020 |
| Orionis Consulting Limited | Information & communication | 2012 |
| Orionz Consulting Limited | Professional & scientific | 2026 |
| Orixy Recycling Ltd | Water & waste | 2025 |
| ORJ55 Ltd | Administrative & support | 2020 |
| Orkinosai Limited | Information & communication | 2025 |
| Orlandi-Fantini Limited | Health & social care | 2003 |
| Orlando Building Services Limited | Wholesale & retail | 2002 |
| Orlijar Active Ltd | Arts & recreation | 2019 |
| Orma Consultancy Limited | Professional & scientific | 2022 |
| Ormerod Telecoms Ltd | Professional & scientific | 2024 |
| Ornare Properties Ltd | Construction | 2026 |
| Oromitope Ltd | Professional & scientific | 2021 |
| Orphic Limited | Wholesale & retail | 2026 |
| Orre Parfums Ltd | Wholesale & retail | 2025 |
| Orridge & Orridge Antiques Limited | Wholesale & retail | 2018 |
| Orridge & Orridge Limited | Wholesale & retail | 2013 |
| Orrken Properties Ltd | Real estate | 2022 |
| Orson Tech Ltd | Construction | 2016 |
| Orston Consulting Limited | Professional & scientific | 2012 |
| Orston Stores Ltd | Wholesale & retail | 2024 |
| Ortasan Limited | Real estate | 2014 |
| Ortho-Thetis Limited | Health & social care | 2012 |
| Orthodontic Studio Limited | Health & social care | 2012 |
| Orthopaedic & Spine Consultancy Limited | Real estate | 2012 |
| Orthopaedic and Injury Clinic Gloucestershire Ltd | Health & social care | 2014 |
| Orthosmart UK Ltd | Manufacturing | 2025 |
| Orthros UK Limited | Professional & scientific | 2008 |
| Ortongate Fitness Limited | Arts & recreation | 2009 |
| Ortongate Management Limited | Administrative & support | 2024 |
| Ortus Housing CIC | Hospitality | 2023 |
| ORU Healthy Life (OHL) Ltd | Health & social care | 2023 |
| Orvarto Ltd | Manufacturing | 2019 |
| Oryson UK Ltd | Construction | 2022 |
| Oryt World Ltd | Information & communication | 2024 |
| OS Wealth Management Limited | Professional & scientific | 2018 |
| Os-Car Direct Ltd | Wholesale & retail | 2023 |
| OSA Consulting Pro Ltd | Professional & scientific | 2025 |
| Osamuede Ltd | Health & social care | 2018 |
| OSB Architects Limited | Professional & scientific | 2017 |
| OSC Property Holding Ltd | Real estate | 2020 |
| Oscar Court (West Bridgford) Ltd | Households | 2020 |
| Oscars Global Limited | Hospitality | 2023 |
| Oscree Homes Limited | Real estate | 2020 |
| OSE Property Ltd | Real estate | 2024 |
| Osemegbe Ehikioya Limited | Health & social care | 2026 |
| Oshi Mart Limited | Manufacturing | 2025 |
| Oshino Lamps (UK) Limited | Wholesale & retail | 1979 |
| Osiris Advisory Limited | Professional & scientific | 2021 |
| Osiris Limited | Other services | 1993 |
| OSK Strategic Solutions Ltd | Professional & scientific | 2025 |
| Oslo Computers Limited | Real estate | 1987 |
| OSM (Leicester) Limited | Construction | 2014 |
| Osman Holdings Limited | Financial services | 2021 |
| Osman Pizza Ltd | Hospitality | 2024 |
| Osmani and Sons Limited | Wholesale & retail | 2017 |