| Oneills Real Estate Ltd | Real estate | 2024 |
| Onetouch Leasing UK Ltd | Information & communication | 2025 |
| Online CEO Ltd | Administrative & support | 2023 |
| Online Empowerment Academy Limited | Education | 2026 |
| Onside Media Limited | Information & communication | 2017 |
| Onward Solutions Ltd | Transport & logistics | 2024 |
| OP Lettings Limited | Real estate | 2006 |
| Opening Doors Limited | Professional & scientific | 2004 |
| Openshaw Properties Limited | Households | 1971 |
| Operational Business Solutions Ltd | Professional & scientific | 2025 |
| Opraas Ltd | Professional & scientific | 2019 |
| Optimal Performance Partners Limited | Health & social care | 2019 |
| Optimised Management Consulting Ltd | Professional & scientific | 2025 |
| Options Property Limited | Real estate | 1997 |
| Optisim Ltd | Professional & scientific | 2013 |
| Optometric Consultancy Ltd. | Health & social care | 2012 |
| Opulent Property Development Ltd | Administrative & support | 2016 |
| Opulent Property Development Middleton Ltd | Construction | 2021 |
| Oral Health Spa Ltd | Health & social care | 2022 |
| ORB Business Solutions Limited | Professional & scientific | 2023 |
| Orbit Worldwide Limited | Information & communication | 2011 |
| Orbital Teal Investments Limited | Real estate | 2025 |
| Orbs Conferences Ltd | Health & social care | 2014 |
| Orchard House Consulting Ltd | Information & communication | 2025 |
| Orchard Investments NW Limited | Real estate | 2021 |
| Orex NW Limited | Arts & recreation | 2019 |
| Organic Eclipse Ltd | Professional & scientific | 2017 |
| Orien Collective Ltd | Wholesale & retail | 2025 |
| Origin Global Limited | Other services | 2016 |
| Original Turkish Barber Ltd | Other services | 2025 |
| Origio Partners Limited | Administrative & support | 2024 |
| Orion Eco Solutions Limited | Manufacturing | 2017 |
| Orion IT Solutions Limited | Information & communication | 2011 |
| Orme Digital Consulting Ltd | Information & communication | 2018 |
| Orme Property Business Ltd | Real estate | 2021 |
| Orrishmere Group Ltd | Information & communication | 2024 |
| Orthofoot Ltd | Health & social care | 2020 |
| Orthoteers Limited | Education | 2004 |
| Ortu Advisors Ltd | Professional & scientific | 2021 |
| Ortu Holdings Limited | Administrative & support | 2024 |
| Orut Ltd | Health & social care | 2015 |
| Osana Studio Ltd | Professional & scientific | 2022 |
| Osborne Court (Ormskirk) Limited | Households | 1982 |
| OSC Group Limited | Financial services | 2016 |
| Ossu Ltd | Hospitality | 2019 |
| Otava Tech Ltd. | Information & communication | 2018 |
| OTE Paintball Ltd | Arts & recreation | 2025 |
| Otis Kent Properties Ltd | Construction | 2018 |
| Otto Vegan Empire Limited | Hospitality | 2022 |
| Otto Ventures Limited | Professional & scientific | 2016 |
| OUR Management Limited | Arts & recreation | 1986 |
| OUR Software Limited | Information & communication | 2013 |
| Ouris Health Ltd | Health & social care | 2017 |
| Ourside Limited | Wholesale & retail | 2026 |
| OUT of the Shadows Choir Ltd | Information & communication | 2019 |
| OUT the HAT (Events) Ltd | Arts & recreation | 2025 |
| Outgoing Limited | Administrative & support | 2000 |
| Outlaw Holdings Ltd | Financial services | 2026 |
| Outreachforyou.Com Limited | Information & communication | 2022 |
| Outsauced Media Ltd | Professional & scientific | 2022 |
| Outside the Box SP Ltd | Professional & scientific | 2019 |
| Ovenlettering Limited | Manufacturing | 2017 |
| Oversley Management Company Limited | Households | 2005 |
| Owoso Consulting Ltd | Professional & scientific | 2026 |
| Oxford Delivery Services Limited | Administrative & support | 2024 |
| Oxford Levant Advisory Limited | Professional & scientific | 2025 |
| Oxford Medico Legal Limited | Health & social care | 2018 |
| Oxford Neurophysiology Ltd | Health & social care | 2023 |
| Oxford Orthodontics Practice Limited | Health & social care | 2022 |
| Oxin Bar and Grill Limited | Hospitality | 2021 |
| Oxmed Consulting Ltd | Professional & scientific | 2026 |
| P Addison Medical Limited | Health & social care | 2017 |
| P B Carter Limited | Health & social care | 2010 |
| P CHO Wellness Ltd | Professional & scientific | 2024 |
| P E M Innovations Ltd | Manufacturing | 2017 |
| P Finan Limited | Health & social care | 2015 |
| P M Sagar Limited | Health & social care | 2014 |
| P R Epoxy Systems Limited | Manufacturing | 1988 |
| P S Lewis Limited | Health & social care | 2011 |
| P Smethurst Limited | Administrative & support | 2014 |
| P T C Medical Limited | Health & social care | 2012 |
| P. Haji-Michael Ltd | Health & social care | 2013 |
| P. J. O' Donovan Limited | Health & social care | 2003 |
| P2 Managed Property Services Ltd | Construction | 2010 |
| Paceline Consulting Limited | Health & social care | 2025 |
| Pact Medical Services Limited | Health & social care | 2020 |
| Padacre Developments Limited | Construction | 2024 |
| Padd Studio Limited | Professional & scientific | 2025 |
| Paddock Smile Centre Ltd | Financial services | 2024 |
| Paddy Mcnair Limited | Construction | 2014 |
| Padel Maintenance Services Ltd | Construction | 2025 |
| Padel Project UK Limited | Arts & recreation | 2023 |
| Padel Ventures Group Limited | Financial services | 2026 |
| Padel Ventures Ltd | Education | 2023 |
| Padelid Ltd | Arts & recreation | 2026 |
| Padmae Holdings Limited | Financial services | 2024 |
| Padmae Property Limited | Wholesale & retail | 2022 |
| Paediatric Heart Rhythm Education and Consulting Limited | Health & social care | 2025 |
| Paediatric IAN NW Limited | Health & social care | 2022 |
| Pagray Medical Limited | Health & social care | 2017 |