| Optimai Labs Ltd | Information & communication | 2025 |
| Optimal 5 Star Limited | Construction | 2009 |
| Optimal Health Performance Limited | Wholesale & retail | 2024 |
| Optimal Holdings Ltd | Health & social care | 2024 |
| Optimal Property Services Limited | Real estate | 2011 |
| Optimates (London) Limited | Administrative & support | 2015 |
| Optimise Management Limited | Professional & scientific | 2026 |
| Optimised Systems Ltd | Information & communication | 2008 |
| Optimising Longevity Ltd | Wholesale & retail | 2026 |
| Optimo Developments Ltd | Real estate | 2024 |
| Optimum Cappuccino Limited | Hospitality | 2011 |
| Optimum Coffee Limited | Hospitality | 2009 |
| Optimum Coffee Services Limited | Hospitality | 2004 |
| Optimum Cooling Solutions Limited | Professional & scientific | 2008 |
| Optimum Cortado Limited | Wholesale & retail | 2018 |
| Optimum Doner Limited | Hospitality | 2021 |
| Optimum Entertainment Ltd | Arts & recreation | 2025 |
| Optimum Espresso Limited | Hospitality | 2022 |
| Optimum Gelato Limited | Hospitality | 2016 |
| Optimum GIO Transport Limited | Transport & logistics | 2025 |
| Optimum Group Employment Limited | Administrative & support | 2024 |
| Optimum Group Holdings Limited | Hospitality | 2018 |
| Optimum Group Properties Limited | Real estate | 2019 |
| Optimum Kitchens and Bedrooms Limited | Administrative & support | 2015 |
| Optimum News Limited | Wholesale & retail | 2023 |
| Optimum Performance Physio Ltd | Health & social care | 2024 |
| Optimum Power Supplies Limited | Administrative & support | 2018 |
| Optimum Ristretto Limited | Hospitality | 2022 |
| Optimum Software Ltd | Information & communication | 1994 |
| Optimum Sports Medicine Ltd | Health & social care | 2017 |
| Optimum Surface Preparation Limited | Construction | 2016 |
| Optimum Tiling Ltd | Construction | 2023 |
| Optimus Business Mentoring and Consulting Ltd | Professional & scientific | 2017 |
| Optimus Consultants NW Limited | Professional & scientific | 2025 |
| Optimus Facilities Holdings Ltd | Financial services | 2026 |
| Optimus Facilities Ltd | Construction | 2020 |
| Optimus Hotel Group CIC | Real estate | 2016 |
| Optimus Hotel Management Limited | Hospitality | 2021 |
| Optimus Hoylake Limited | Transport & logistics | 2021 |
| Optimus Rodney Street Ltd | Financial services | 2021 |
| Options Beauty Therapy Centres Limited | Real estate | 1995 |
| Options for Supported Living | Health & social care | 1993 |
| Optipark Ltd | Professional & scientific | 2020 |
| Optivance Ltd | Information & communication | 2025 |
| Optivo Developments Ltd | Construction | 2023 |
| Optix Utility Management Ltd | Professional & scientific | 2024 |
| Optoplast Actman Group Ltd | Wholesale & retail | 2011 |
| Optus Exactus Limited | Construction | 2025 |
| Opulence Voyage Limited | Transport & logistics | 2022 |
| Opulence Wedding and Event Planning Ltd | Wholesale & retail | 2016 |
| Opulent @ 35 Ltd | Hospitality | 2025 |
| Opulent Lifts Ltd | Manufacturing | 2020 |
| Opus Academy CIC | Education | 2025 |
| Opus Aluminium Systems Ltd | Manufacturing | 2023 |
| Opus Artistry Ltd | Administrative & support | 2021 |
| Opus Care Group Ltd | Health & social care | 2024 |
| Opus Energy Marketing Limited | Energy | 2004 |
| Opus Events Limited | Wholesale & retail | 2009 |
| Opus Holdings Limited | Real estate | 2022 |
| Opus Homewares Limited | Real estate | 2003 |
| Opus Trading Limited | Construction | 2006 |
| Opus Wills LLP | | 2013 |
| Opusmodus Limited | Information & communication | 2012 |
| OR Bold Street Limited | Hospitality | 2021 |
| OR Construction Ltd | Construction | 2020 |
| OR Moshe Ltd | Information & communication | 2022 |
| OR Walks Group Limited | Hospitality | 2019 |
| OR Walks Holdings Limited | Financial services | 2014 |
| ORA Body and Skin Collections Ltd | Wholesale & retail | 2020 |
| ORA Health Ltd | Administrative & support | 2017 |
| Oracle Bounce Limited | Financial services | 2024 |
| Oracle Business Services Ltd | Administrative & support | 2011 |
| Oracle Link Ltd | Professional & scientific | 2016 |
| Oracle Property Group Limited | Real estate | 2020 |
| Oracleforecast Ltd | Arts & recreation | 2013 |
| Orakl Ltd | Wholesale & retail | 2025 |
| Oralogic Limited | Administrative & support | 2021 |
| Orange County Services Limited | Administrative & support | 2015 |
| Orange Investments (NW) Limited | Real estate | 2022 |
| Orange Mint Consultancy Ltd | Professional & scientific | 2024 |
| Orange Mountain Bikes Limited | Wholesale & retail | 1988 |
| Orange Professional Services Limited | Construction | 2008 |
| Orange Property Services (Liverpool) Limited | Real estate | 2012 |
| Orange Rentals Property Management Ltd | Hospitality | 2024 |
| Orange River Estates Ltd | Real estate | 2019 |
| Orangepeel Solutions Ltd | Wholesale & retail | 2024 |
| Oraura Beauty & Black Swan Inkk Ltd | Other services | 2023 |
| ORB Event Agency Ltd | Construction | 2018 |
| Orbilimited Ltd | Other services | 2026 |
| Orbis 1 Limited | Health & social care | 2025 |
| Orbis Asset Integrity Ltd | Administrative & support | 2011 |
| Orbis Travel Holidays Ltd | Administrative & support | 2021 |
| Orbit Rides Ltd | Transport & logistics | 2024 |
| Orbitica Ltd | Wholesale & retail | 2024 |
| Orbs Holdings Limited | Financial services | 2024 |
| Orcauk Ltd | Transport & logistics | 2024 |
| Orchard Construction & Development Ltd | Construction | 2020 |
| Orchard Dene Management Limited | Households | 1978 |
| Orchard Developments Liverpool Limited | Construction | 2019 |
| Orchard Gate (Oxton) Management Company Limited | Households | 2005 |