| Orosimo Investments Limited | Real estate | 2022 |
| ORP Digital Marketing Limited | Professional & scientific | 2019 |
| Orphic Systems Limited | Information & communication | 1996 |
| Orrington Global Ltd | Professional & scientific | 2024 |
| ORS Flooring Ltd | Construction | 2017 |
| Orsam Ltd | Health & social care | 2024 |
| Orso Eatery Limited | Hospitality | 2019 |
| Orston Spectacular Ltd | Transport & logistics | 2015 |
| Orthodocs Private Ltd | Health & social care | 2015 |
| Orthodocs Properties Limited | Real estate | 2017 |
| Orthorehab UK Ltd | Health & social care | 2025 |
| Ortu Group Limited | Financial services | 2021 |
| Orva Ltd | Wholesale & retail | 2025 |
| Orygin Trading Co Ltd | Wholesale & retail | 2023 |
| Oryx Properties (Leic) Ltd | Real estate | 2023 |
| OS (Leicester) Ltd | Hospitality | 2022 |
| Os.Sa Properties Limited | Real estate | 2023 |
| Osara Limited | Hospitality | 2018 |
| Osborne House Property Management Limited | Other services | 2011 |
| Osbro Properties Ltd | Real estate | 2020 |
| OSC Education Ltd | Education | 2016 |
| Oscar Leics Ltd | Wholesale & retail | 2021 |
| Oscar Supermarket Ltd | Wholesale & retail | 2017 |
| Oscar Uppingham Ltd | Wholesale & retail | 2019 |
| Osce Toolbox Ltd | Education | 2024 |
| Osemudia Limited | Administrative & support | 2019 |
| Osgathorpe Grange Management Company Limited | Real estate | 2017 |
| Oshaesh Ltd | Real estate | 2016 |
| Oshea Consulting Limited | Information & communication | 2018 |
| Oshera Palace Ltd | Wholesale & retail | 2025 |
| Oshumade Limited | Real estate | 2015 |
| Osiris Tech Limited | Information & communication | 2025 |
| Oskar Car Ltd | Wholesale & retail | 2023 |
| OSL Holdings Limited | Professional & scientific | 2002 |
| Oslo Holdings Limited | Professional & scientific | 2023 |
| OSM Investments Limited | Financial services | 2022 |
| OSM Properties Limited | Real estate | 2021 |
| OSM Property Developments Limited | Real estate | 2024 |
| Osman Assets Limited | Real estate | 2022 |
| Osman Design Partnership Ltd | Professional & scientific | 2016 |
| Osman Enterprise Ltd | Transport & logistics | 2020 |
| Osman Estate Management Ltd | Financial services | 2026 |
| Osman Housings Limited | Construction | 2022 |
| Osman Properties Limited | Real estate | 2021 |
| Osman Solutions Limited | Health & social care | 2025 |
| Osmans Property Ltd | Real estate | 2020 |
| Osnn Properties Limited | Real estate | 2026 |
| Osoble Ltd | Health & social care | 2022 |
| Osra Ltd | Real estate | 2022 |
| Ostroluxx Ltd | Manufacturing | 2025 |
| Oswin Enterprises Ltd | Wholesale & retail | 2026 |
| Oswin Frost Group Ltd | Wholesale & retail | 2023 |
| Oswin Frost Holdings Ltd | Professional & scientific | 2021 |
| Oswin Property Ltd | Real estate | 2018 |
| OSX Investments Limited | Real estate | 2019 |
| Otapo Ltd | Information & communication | 2019 |
| OTI & Lion Limited | Professional & scientific | 2023 |
| Otilia Property Group Ltd | Real estate | 2026 |
| Otis E&M Company Limited | Professional & scientific | 1911 |
| Otis Elevator Holdings Limited | Professional & scientific | 1963 |
| Otis International Holdings UK Limited | Professional & scientific | 1991 |
| Otis Investments Limited | Professional & scientific | 1900 |
| Otis Limited | Manufacturing | 1917 |
| Otis UK Holding Limited | Professional & scientific | 2006 |
| OTM Power Generation Ltd | Energy | 2024 |
| Otpd Leicester Ltd | Real estate | 2026 |
| Otro Club Limited | Information & communication | 2016 |
| Otro Global Limited | Information & communication | 2018 |
| OTS Media Ltd | Information & communication | 2022 |
| Ottima Hardware Ltd | Wholesale & retail | 2009 |
| Otto Property Holdings Ltd | Real estate | 2016 |
| Ottrix Limited | Administrative & support | 2022 |
| OUD Banq Limited | Wholesale & retail | 2026 |
| Oudara Ltd | Wholesale & retail | 2026 |
| OUI Love Trips Ltd | Education | 2018 |
| OUI MON Cheri Ltd | Wholesale & retail | 2018 |
| Oulston Ltd | Other services | 2015 |
| OUM Haroun Airbnb Cleaner Ltd | Other services | 2025 |
| OUR Family Foods UK Limited | Manufacturing | 2023 |
| OUR Gifts Ltd | Health & social care | 2014 |
| OUR Perfect Place Ltd | Real estate | 2025 |
| Ousby Assignments Ltd | Transport & logistics | 2015 |
| OUT of India Shepshed Ltd | Hospitality | 2018 |
| OUT of Joint Ltd | Wholesale & retail | 2023 |
| Outbuilding Ltd | Hospitality | 2025 |
| Outfit Clothing Limited | Wholesale & retail | 2017 |
| Outfox the Market Limited | Extraterritorial | 2018 |
| Outfox Utilities Ltd | Information & communication | 2025 |
| Outgrowth Titans Limited | Wholesale & retail | 2022 |
| Outland Projects Limited | Real estate | 2005 |
| Outland Property Management Ltd | Households | 2025 |
| Outlandish Items Limited | Wholesale & retail | 2005 |
| Outlet Consultants Ltd | Education | 2021 |
| Outlook Jewellery Ltd | Wholesale & retail | 2024 |
| Outlook Partnerships Limited | Professional & scientific | 2001 |
| Outonthelash Ltd | Other services | 2025 |
| Outreach Sign Services Limited | Construction | 1999 |
| Outsource Bookkeeping & Tax Solutions Ltd | Professional & scientific | 2025 |
| Outsource Bookkeeping Solutions Ltd | Professional & scientific | 2021 |
| Outsourced PMO Ltd | Administrative & support | 2023 |