| Operam Education Tutoring Limited | Education | 2021 |
| Operam Tutoring Limited | Education | 2021 |
| Opes Libertas Ltd | Real estate | 2015 |
| Ophthalmic Associates Derby Limited | Real estate | 2012 |
| Oppian Systems Limited | Information & communication | 2009 |
| Optical Hardware Limited | Administrative & support | 2005 |
| Optima Property Group Ltd | Real estate | 2026 |
| Optima Safety Solutions Ltd | Professional & scientific | 2018 |
| Optimal Contracting Services Ltd | Construction | 2023 |
| Optimal MIX Ltd | Hospitality | 2025 |
| Optimise Cyber Solutions Ltd | Education | 2024 |
| Optimo (Properties 2) Limited | Real estate | 2025 |
| Optimo (Properties) Limited | Health & social care | 2024 |
| Optimo (SL Holdco) Limited | Health & social care | 2022 |
| Optimo Care Group Limited | Health & social care | 2010 |
| Optimum Timber Supplies Limited | Wholesale & retail | 2003 |
| Orad Services Limited | Construction | 2020 |
| Oraia Limited | Real estate | 2025 |
| Orbisedge Ltd | Information & communication | 2025 |
| Orbital Management Services Limited | Administrative & support | 2007 |
| Orbital Management Systems Limited | Professional & scientific | 2009 |
| Orbital Payroll Group Limited | Administrative & support | 2014 |
| Orbital Professional Employment Limited | Administrative & support | 2020 |
| Orbital Umbrella Limited | Administrative & support | 2010 |
| Orchard Cost Consultants Limited | Professional & scientific | 2014 |
| Orchard Court Flats Management Limited | Households | 1985 |
| Orchard Croft Management (Yorkshire) Limited | Households | 2021 |
| Orchard HSE Ltd | Professional & scientific | 2015 |
| Orchid Installations Limited | Construction | 2003 |
| Orchid Storage Limited | Administrative & support | 2016 |
| Order Doors Online Limited | Construction | 2024 |
| Oriel Placements Ltd | Administrative & support | 2017 |
| Origen Works Ltd | Professional & scientific | 2026 |
| Original E-Cigs Company Limited | Wholesale & retail | 2014 |
| Orion Investment Group Limited | Real estate | 2019 |
| Orion Projects Group Ltd | Construction | 2024 |
| Orion Property Solutions (OPS) Ltd | Real estate | 2020 |
| Orison Health Ltd | Health & social care | 2020 |
| Ormand Distribution Services Limited | Transport & logistics | 2016 |
| ORO Automotive Limited | Wholesale & retail | 2025 |
| Orthotic Biomechanical Solutions Limited | Health & social care | 2008 |
| Orthowizard Limited | Health & social care | 2019 |
| Osborne Technologies Ltd | Information & communication | 1998 |
| Oscar Tango Charlie Limited | Wholesale & retail | 2019 |
| OSJ Motor Company Limited | Wholesale & retail | 2015 |
| Ossett Digital Ltd | Information & communication | 2025 |
| Ostec Limited | Professional & scientific | 2014 |
| OT13 Ltd | Wholesale & retail | 2025 |
| Otter Tots Swim School Limited | Arts & recreation | 2012 |
| Otto Trans-Speed Ltd | Transport & logistics | 2018 |
| OTW Business Limited | Information & communication | 2014 |
| OUR Circle AF Ltd | Health & social care | 2023 |
| OUR Little Stars CIC | Other services | 2025 |
| Outhouse Brewing Ltd | Manufacturing | 2017 |
| Outstanding Care Services Limited | Information & communication | 2019 |
| Outwin Properties Limited | Real estate | 2018 |
| Overball Limited | Households | 1986 |
| Overcocoon Ltd | Wholesale & retail | 2022 |
| Overhead Roofing Limited | Construction | 2023 |
| Override Group Ltd | Professional & scientific | 2026 |
| OVI 19 Ltd | Transport & logistics | 2026 |
| Ovidiu Security Ltd | Administrative & support | 2021 |
| Owen & Co (Properties) Limited | Real estate | 2001 |
| Owen Electrical Services Limited | Construction | 2023 |
| Owen Fraser Properties Ltd | Real estate | 2021 |
| OWL Strategy Consulting Ltd | Information & communication | 2023 |
| Own IT Properties Ltd | Real estate | 2026 |
| Oxley Roofing Limited | Construction | 2026 |
| Oxleys Commercial & Industrial Window Cleaning Limited | Other services | 2005 |
| Oxygen Electric Bikes Limited | Wholesale & retail | 2014 |
| O’Connor Logistics Ltd | Wholesale & retail | 2026 |
| P & a S Hayselden Limited | Construction | 2003 |
| P & G Properties (Barnsley) Limited | Real estate | 1996 |
| P & J Property Solutions Limited | Real estate | 2019 |
| P & M (Maxey) Limited | Financial services | 2017 |
| P & P Auto Engineers Limited | Wholesale & retail | 2003 |
| P & P Holdings Yorkshire Limited | Other services | 2017 |
| P & P Nail Grimethorpe Ltd | Other services | 2025 |
| P and J Alderton Ltd | Hospitality | 2022 |
| P B Catering Engineer Ltd | Manufacturing | 2007 |
| P Biddlestone Groundworks & Maintenance Limited | Construction | 2007 |
| P Bond Building Contractors Limited | Construction | 2004 |
| P D GAP Ltd | Construction | 2026 |
| P H Heating.Co.Uk Ltd | Construction | 2016 |
| P Hartley Clinic of Physiotherapy Ltd | Other services | 2004 |
| P J & R Mccool Limited | Hospitality | 2003 |
| P J Plant & Equipment Limited | Water & waste | 1998 |
| P M Computing Limited | Information & communication | 1996 |
| P N Joinery Services Limited | Construction | 2019 |
| P R Hobson Properties Limited | Construction | 2004 |
| P Sephton Transport Limited | Transport & logistics | 2014 |
| P Turner and Sons Limited | Manufacturing | 2017 |
| P&E Gibson Investments Limited | Real estate | 2023 |
| P&E Pets Ltd | Professional & scientific | 2025 |
| P&J Medical Limited | Health & social care | 2022 |
| P&Jm Consulting Limited | Real estate | 2018 |
| P. Hinchliffe Limited | Professional & scientific | 2009 |
| P. Jenkins Services Limited | Information & communication | 2025 |
| P. Zawlik Ltd | Transport & logistics | 2014 |
| P.A.D Utilities Ltd | Energy | 2018 |