| Oscar Masood Limited | Information & communication | 2023 |
| Oscar's Cafe Limited | Hospitality | 2024 |
| Oscars Holdina Limited | Hospitality | 2017 |
| Oscorb Ltd | Wholesale & retail | 2022 |
| Osiris Engineering Limited | Extraterritorial | 2020 |
| Oskarx Limited | Information & communication | 2025 |
| Oslo IT Consultancy Ltd | Information & communication | 2017 |
| Osman Medical Services Limited | Health & social care | 2024 |
| Osmani’S Ltd | Wholesale & retail | 2026 |
| Osmium Candle Company Ltd | Manufacturing | 2024 |
| Osprey System Solutions Limited | Professional & scientific | 2017 |
| Ossington IT Ltd | Information & communication | 2025 |
| Osynachi Limited | Health & social care | 2023 |
| Otco Investments Limited | Real estate | 2026 |
| Otco Retail Limited | Wholesale & retail | 2026 |
| Oti's Coffee Ltd | Hospitality | 2026 |
| Otis Cleaning Services Ltd | Administrative & support | 2022 |
| Otium Ltd | Professional & scientific | 2011 |
| Otterseas Ltd | Wholesale & retail | 2024 |
| Otto & Co Limited | Information & communication | 2013 |
| Otwr Ltd | Manufacturing | 2022 |
| OUD Brothers Ltd | Wholesale & retail | 2024 |
| OUR Cloud Network Ltd | Information & communication | 2023 |
| OUR Little Place Cafe Ltd | Hospitality | 2025 |
| Ourkid Investments Limited | Administrative & support | 2024 |
| OUT of Hours Healthcare Ltd | Health & social care | 2015 |
| OUT With the WAX Ltd | Health & social care | 2023 |
| Outcomes First 1 Limited | Financial services | 2010 |
| Outcomes First 2 Limited | Financial services | 2010 |
| Outcomes First 3 Limited | Financial services | 2010 |
| Outcomes First 4 Limited | Financial services | 2010 |
| Outcomes First 6 Limited | Financial services | 2025 |
| Outcomes First 6 Subco Limited | Financial services | 2025 |
| Outcomes First Group (Operations) 1 Limited | Education | 2024 |
| Outcomes First Group (Operations) 2 Limited | Education | 2024 |
| Outcomes First Group (Operations) 3 Limited | Education | 2000 |
| Outcomes First Group (Operations) 4 Limited | Health & social care | 2005 |
| Outcomes First Group Holdings Limited | Administrative & support | 2013 |
| Outcomes First Midco Limited | Administrative & support | 2013 |
| Outer Consultancy Ltd | Professional & scientific | 2024 |
| Outer Space Storage Centres (Farnworth) Limited | Transport & logistics | 2013 |
| Outerform Fabrications Limited | Manufacturing | 2012 |
| Outlet Cricket Limited | Wholesale & retail | 2019 |
| Outline Health & Fitness Ltd | Arts & recreation | 2015 |
| Outline Social Marketing Ltd | Professional & scientific | 2026 |
| Outshine Outsource Limited | Administrative & support | 2015 |
| Oval Project Management Limited | Construction | 2022 |
| Ovenden Trading Ltd | Wholesale & retail | 2022 |
| Over Clothing Limited | Wholesale & retail | 2025 |
| Over to YOU Ceremonies Ltd. | Other services | 2018 |
| Overarc Limited | Professional & scientific | 2024 |
| Overarch Brands Ltd | Wholesale & retail | 2022 |
| Overcoming Obstacles Ltd | Education | 2022 |
| Overflowing Riches of Christ Church and Ministry International Limited | Health & social care | 2020 |
| Overratted Rates Ltd | Administrative & support | 2019 |
| Overtime Cleaning Limited | Administrative & support | 2021 |
| OVJ Limited | Construction | 2024 |
| Ovuike Legal Services Ltd | Professional & scientific | 2015 |
| Owaisi Travels Ltd | Administrative & support | 2025 |
| Owenabue Limited | Professional & scientific | 2021 |
| Owenlets Ltd | Real estate | 2025 |
| Own Your Space Limited | Administrative & support | 2015 |
| Owners Club Bidco Limited | Administrative & support | 2024 |
| Owners Club Topco Limited | Administrative & support | 2024 |
| Oxbys Autos Ltd | Wholesale & retail | 2022 |
| Oxford Montessori Schools Limited | Education | 2013 |
| Oxford Specialist Anaesthesia Limited | Health & social care | 2015 |
| Oxford Street Real Estate Limited | Real estate | 2021 |
| Oxfordshire Projects Ltd | Construction | 2024 |
| Oxijan Ltd | Wholesale & retail | 2019 |
| Oxino Ltd | Wholesale & retail | 2021 |
| Oxiti Ltd | Information & communication | 2023 |
| Oxmark Ltd | Manufacturing | 2025 |
| Oxpot (Deansgate) Ltd | Hospitality | 2025 |
| Oxsed Limited | Manufacturing | 2020 |
| Oxy-Plants Ltd | Wholesale & retail | 2020 |
| Oxygen Manchester Ltd | Real estate | 2022 |
| Oyaah Ltd | Wholesale & retail | 2023 |
| OYI Onmonya Ltd | Real estate | 2024 |
| Oyster Catcher Estates Ltd | Real estate | 2024 |
| OZ Candles Limited | Manufacturing | 2015 |
| OZE Sports Limited | Wholesale & retail | 2022 |
| Ozel Barber Ltd | Other services | 2024 |
| OZI CC Limited | Hospitality | 2025 |
| Ozoneai Ltd | Information & communication | 2026 |
| Ozzy Property Solutions Ltd | Construction | 2026 |
| O`Donnell Joinery Limited | Extraterritorial | 2008 |
| O’Gorman Rail Services Ltd | Construction | 2025 |
| O’Neill LET Limited | Real estate | 2020 |
| P & B Northwest Services Limited | Health & social care | 2013 |
| P & D Heating & Bathrooms Limited | Construction | 2009 |
| P & J Electrical (NW) Ltd | Construction | 2011 |
| P & K Shutter Services Limited | Manufacturing | 1999 |
| P & L Property Services (NW) Limited | Real estate | 2024 |
| P & P Cleaning Services Limited | Administrative & support | 2010 |
| P & P Electrical and Plumbing Limited | Construction | 2024 |
| P & P Food N Wine Limited | Wholesale & retail | 2006 |
| P & P Tiling Ltd | Construction | 2013 |
| P & R Plant Ltd | Administrative & support | 2012 |
| P & S Domestics (Holdings) Limited | Wholesale & retail | 2021 |