| Oakwood Construction (Northern) Ltd | Construction | 2014 |
| Oakwood Group Limited | Financial services | 2022 |
| Oakwood Property Ltd | Real estate | 2023 |
| Oakwoods Construction Group Limited | Construction | 2022 |
| OAR Caterer Ltd | Hospitality | 2023 |
| OAR Catering Limited | Hospitality | 2019 |
| Oarachnis Group Limited | Information & communication | 2025 |
| Oasis Architects Ltd | Professional & scientific | 2023 |
| Oasis Bar Limited | Hospitality | 2019 |
| Oasis Beauty Salon Ltd | Other services | 2024 |
| Oasis Hair Sun & Beauty Limited | Other services | 2018 |
| Oasis Lettings Ltd | Real estate | 2023 |
| Oasis Property Partners Limited | Financial services | 2015 |
| Oasis Systems Ltd | Administrative & support | 2018 |
| Oasis Trading (London) Limited | Wholesale & retail | 2001 |
| Oastdren Securities Limited | Real estate | 1964 |
| OAT Groundworks Ltd | Construction | 2025 |
| Oates Construction Ltd | Construction | 2022 |
| Oatland Group Limited | Financial services | 2024 |
| Oatland Properties Limited | Real estate | 2024 |
| Oatlands Academy C.I.C. | Education | 2023 |
| Oavven Ltd | Health & social care | 2026 |
| OB Metals Ltd | Water & waste | 2025 |
| OB Mortgages Ltd | Financial services | 2024 |
| OB Skips and Recycling Ltd | Water & waste | 2019 |
| OB Surveyors Ltd | Professional & scientific | 2026 |
| Obadina Ltd | Wholesale & retail | 2024 |
| Oban Construction (NW) Limited | Construction | 2022 |
| Oban Design Limited | Professional & scientific | 2017 |
| OBC Liverpool Ltd | Wholesale & retail | 2020 |
| Obdfilms Limited | Information & communication | 2017 |
| Obe's Taste of Africa Ltd | Hospitality | 2023 |
| OBE6 Limited | Other services | 2020 |
| Obet Ltd | Wholesale & retail | 2024 |
| Obe’S Kitchen Street Food Limited | Hospitality | 2026 |
| OBG Consumer REG Scientific Limited | Professional & scientific | 2020 |
| OBG Consumer Scientific Limited | Manufacturing | 2020 |
| OBG Estates Limited | Real estate | 2026 |
| OBG Finance Holding Limited | Financial services | 2016 |
| OBG Finance Limited | Financial services | 2016 |
| OBG Holding Limited | Manufacturing | 2016 |
| OBG Property Holding Limited | Real estate | 2016 |
| OBG Scientific Division Limited | Administrative & support | 2016 |
| OBI Gold Global Resources Limited | Health & social care | 2024 |
| Obiq Ltd | Information & communication | 2026 |
| Obiteddy Healthcare Staffing Limited | Administrative & support | 2015 |
| Obium Global Limited | Wholesale & retail | 2025 |
| OBK Lettings Ltd | Real estate | 2023 |
| OBL Brickwork Ltd | Construction | 2021 |
| Obrien Electrical Services Ltd | Other services | 2017 |
| Obrien Housing Ltd | Real estate | 2023 |
| Obriens Motor Company Ltd | Wholesale & retail | 2018 |
| Obscenic Ltd. | Information & communication | 2013 |
| Obsidian Secure Ltd | Information & communication | 2025 |
| OBT Code Ltd | Information & communication | 2024 |
| Obys Construction Consultants Limited | Professional & scientific | 2024 |
| OC Developments Limited | Real estate | 2023 |
| OC Recruitment Limited | Administrative & support | 2023 |
| Ocam Installations UK Limited | Construction | 2006 |
| Ocana People Solutions Ltd | Administrative & support | 2019 |
| Occasio Investments Ltd | Financial services | 2026 |
| Occasio Property Ltd | Real estate | 2023 |
| Occasion Works Ltd | Administrative & support | 2026 |
| Occasions Travel Ltd | Transport & logistics | 2026 |
| Occupational Safety Academy Limited | Professional & scientific | 2026 |
| OCD Event Management Ltd | Administrative & support | 2019 |
| Ocean Blue Jewellery Ltd. | Wholesale & retail | 1998 |
| Ocean Company Care Ltd | Health & social care | 2024 |
| Ocean Design & Bespoke Contracts Ltd | Construction | 2010 |
| Ocean Developments (NW) Ltd | Construction | 2018 |
| Ocean EYE Technology Limited | Transport & logistics | 2024 |
| Ocean Hospitality Ltd | Arts & recreation | 2021 |
| Ocean Oak Ltd | Professional & scientific | 2023 |
| Ocean Park Limited | Hospitality | 2013 |
| Ocean Products (Liverpool) Limited | Wholesale & retail | 2007 |
| Ocean Property Homes Ltd | Real estate | 2024 |
| Ocean Sefton Road Ltd | Hospitality | 2025 |
| Ocean Titan Solutions Ltd | Information & communication | 2022 |
| Oceancross Limited | Administrative & support | 2003 |
| Oceandom Ltd | Arts & recreation | 2023 |
| Oceanexpress Limited | Transport & logistics | 1987 |
| Oceaneyes Ltd | Professional & scientific | 2019 |
| Oceanic White Star Trading Co Ltd | Hospitality | 2012 |
| Oceann Hand Car Wash Ltd | Administrative & support | 2026 |
| Oceanview Entertainment Ltd | Arts & recreation | 2023 |
| Oceanz Ecosystems Limited | Professional & scientific | 2025 |
| Ocha Building Renovation Ltd | Construction | 2024 |
| Ociusnet UK Ltd | Construction | 2018 |
| Ockleybrook Trading Limited | Professional & scientific | 2018 |
| OCO Bookkeeping Limited | Professional & scientific | 2020 |
| OCO Properties Limited | Real estate | 2020 |
| OCO Property Services Ltd | Real estate | 2020 |
| OCO Tools Ltd | Wholesale & retail | 2020 |
| Ocsel Ltd | Wholesale & retail | 2025 |
| Octaive Holdings Limited | Information & communication | 2019 |
| Octave (NW) Ltd | Construction | 2015 |
| Octavia Properties Limited | Households | 2025 |
| Octavian Moda Ltd | Wholesale & retail | 2019 |
| Octen Limited | Real estate | 2011 |
| Octex Digital Limited | Information & communication | 2025 |