| Oakmeadow Care Ltd | Health & social care | 2024 |
| Oakmeadow Properties Ltd | Real estate | 2016 |
| Oakmere Capital Limited | Real estate | 2026 |
| Oakridge Health Ltd | Health & social care | 2025 |
| Oaks Media Limited | Information & communication | 2013 |
| Oaksbridge Residential Ltd | Households | 2025 |
| Oakside Group Holdings Limited | Financial services | 2020 |
| Oakstone Structures Ltd | Construction | 2021 |
| Oaksway Property Limited | Manufacturing | 1991 |
| Oaktarget Limited | Manufacturing | 1987 |
| Oaktree Connect Ltd | Health & social care | 2021 |
| Oaktree Homehelp Ltd | Health & social care | 2021 |
| Oaktree Mortgages Ltd | Financial services | 2003 |
| Oakwood House Management Company (Leicester) Limited | Households | 2004 |
| Oases Bar Ltd | Hospitality | 2025 |
| Oasis Co-Living Limited | Real estate | 2017 |
| Oasis Developments Limited | Real estate | 2017 |
| Oasis Group Leicester Limited | Financial services | 2026 |
| Oasis Habesha Ltd | Wholesale & retail | 2022 |
| Oasis Holdings Limited | Real estate | 2017 |
| Oasis Lounge Ltd | Hospitality | 2025 |
| Oasis Minimarket Ltd | Wholesale & retail | 2020 |
| OAT Hill Homes Ltd | Construction | 2020 |
| Oathill New Homes Ltd | Real estate | 2023 |
| OBA Consult Ltd | Other services | 2016 |
| Obadtech Ltd | Wholesale & retail | 2025 |
| Oban Hotel Limited | Hospitality | 2020 |
| OBC Lean Solutions Limited | Professional & scientific | 2017 |
| Obeant Limited | Professional & scientific | 2025 |
| Obelisk Display Systems Limited | Administrative & support | 2017 |
| Oben Hoch Ltd | Wholesale & retail | 2021 |
| Obepoet Ltd | Transport & logistics | 2026 |
| OBF Foods Limited | Hospitality | 2026 |
| Obiera Ltd | Wholesale & retail | 2025 |
| Obigbonine/Nile Ltd | Education | 2025 |
| Obioha Properties Ltd | Real estate | 2023 |
| Obiuz Limited | Information & communication | 2009 |
| Objify Ltd | Information & communication | 2025 |
| Objk Developments Limited | Construction | 2021 |
| Objk Limited | Real estate | 2021 |
| Oblio and Arrow Ltd | Professional & scientific | 2024 |
| OBM Solutions Ltd | Professional & scientific | 2021 |
| Obnisha Limited | Mining & quarrying | 2024 |
| OBP Consultancy Ltd | Wholesale & retail | 2018 |
| Obscure Clothing Ltd | Wholesale & retail | 2009 |
| Obsequio Group Limited | Financial services | 2022 |
| Obsequio Group Parent Limited | Financial services | 2020 |
| Obsidian Group Limited | Financial services | 2016 |
| Obsidian Pension Administration Ltd | Professional & scientific | 2015 |
| Obsidian Tax Limited | Professional & scientific | 2020 |
| Obsidianw Limited | Manufacturing | 2024 |
| Obsidiyon Ltd | Wholesale & retail | 2022 |
| Obstrat Ltd | Professional & scientific | 2016 |
| OBT Consultants Ltd | Construction | 2021 |
| Obtain Limited | Administrative & support | 2025 |
| Obviate Ltd | Professional & scientific | 2024 |
| Obvs Fresh Ltd | Wholesale & retail | 2024 |
| OCB Media Limited | Information & communication | 2002 |
| OCB Publishing Limited | Information & communication | 2005 |
| OCC QS Limited | Other services | 2013 |
| Ocean 7 Consulting Ltd | Financial services | 2013 |
| Ocean Bay Holdings Limited | Financial services | 2022 |
| Ocean Breeze Limited | Wholesale & retail | 2017 |
| Ocean Chippy Limited | Hospitality | 2026 |
| Ocean Co 1 Limited | Hospitality | 2025 |
| Ocean Co Holdings Limited | Financial services | 2024 |
| Ocean Construction (Leicester) Limited | Construction | 2019 |
| Ocean Duty Free Limited | Other services | 2023 |
| Ocean Food (Leic) Ltd | Hospitality | 2017 |
| Ocean Haze Ltd | Wholesale & retail | 2025 |
| Ocean INV Ltd | Real estate | 2020 |
| Ocean Pantry Limited | Hospitality | 2015 |
| Ocean Renown Ltd | Wholesale & retail | 2024 |
| Ocean Road Limited | Construction | 2020 |
| Ocean to Ocean Property Management Limited | Real estate | 2007 |
| Oceana Sky Ltd | Real estate | 2011 |
| Oceandata Limited | Information & communication | 1996 |
| Oceands Healthcare Ltd | Health & social care | 2023 |
| Oceanpure Solutions Ltd | Administrative & support | 2026 |
| Oceanview Realty Ltd | Real estate | 2025 |
| Ocellus Holdings Limited | Financial services | 2024 |
| OCM Kitchens and Bedrooms Limited | Construction | 2025 |
| OCP (UK) Limited | Construction | 2011 |
| OCP Hadleigh RTM Company Limited | Real estate | 2026 |
| Ocpt Propco Limited | Hospitality | 2025 |
| OCR Networks Ltd | Administrative & support | 2016 |
| Octagon Risk Management Ltd | Administrative & support | 2024 |
| OCTAGRAM16 Ltd | Real estate | 2023 |
| Octas LLP | | 2007 |
| Octavian DLV Ltd | Transport & logistics | 2020 |
| Octavie BEI Limited | Health & social care | 2019 |
| Octevo Housing Solutions Limited | Real estate | 2016 |
| Octo Move Ltd | Real estate | 2025 |
| October Productions Limited | Financial services | 1998 |
| Octoglass Ltd | Construction | 2022 |
| Octothera Consumer Healthcare Limited | Health & social care | 2017 |
| Ocularize Ltd | Administrative & support | 2021 |
| Ocutech Limited | Health & social care | 2017 |
| OD Leicester Ltd | Hospitality | 2021 |
| OD Maths Ltd | Education | 2023 |