| OJ Bespoke Tiling Ltd | Construction | 2025 |
| OJ Fabtek Ltd | Wholesale & retail | 2024 |
| OJL Services Limited | Administrative & support | 2015 |
| OL Holdings Limited | Administrative & support | 2018 |
| OLA Shop Ltd | Wholesale & retail | 2025 |
| Old Astwood Limited | Administrative & support | 2013 |
| Old Swan Moorings Limited | Administrative & support | 2020 |
| Olive Olive | Real estate | 2019 |
| Olive Olive Holdings | Financial services | 2019 |
| Oliveira Property Ltd | Real estate | 2023 |
| Olympuss Ltd | Hospitality | 2025 |
| Omni Signage Services Ltd | Professional & scientific | 2019 |
| Omnilea Ltd | Wholesale & retail | 2025 |
| Omniplen Trade Limited | Wholesale & retail | 2026 |
| On-Track Tuition Ltd | Education | 2021 |
| Onco Recruit Limited | Administrative & support | 2010 |
| Ondie Limited | Agriculture & fishing | 2017 |
| One Floor Limited | Wholesale & retail | 2003 |
| One More One Productions Limited | Administrative & support | 2015 |
| One Step at a Time Footcare Limited | Other services | 2024 |
| One Vision Architectural Ltd | Construction | 2022 |
| Onemaxx Services Limited | Wholesale & retail | 2020 |
| Oneonesix Developments Limited | Construction | 2013 |
| Onetouch Cleaning Services Ltd | Administrative & support | 2025 |
| Online Toy Shop Limited | Wholesale & retail | 2010 |
| Onlinecube Limited | Wholesale & retail | 2025 |
| Only Marjorie Ltd | Manufacturing | 2019 |
| Onwuzurike Surveying Consultancy Ltd | Professional & scientific | 2025 |
| Onyx Construction Kent Ltd | Construction | 2021 |
| Open Catering Limited | Hospitality | 2022 |
| Open Hospitality Managment Limited | Hospitality | 2022 |
| Open Restaurant Group Limited | Financial services | 2024 |
| Open Sky Consulting Limited | Professional & scientific | 2013 |
| Open Software Group Ltd | Financial services | 2025 |
| Optimised Care Holdings Ltd | Public administration | 2025 |
| Optimised Care Limited | Health & social care | 2018 |
| Optimised Wellness Ltd | Public administration | 2025 |
| Optimum Telecom Limited | Information & communication | 2008 |
| Optivus Enterprises Ltd | Wholesale & retail | 2025 |
| Orange and Blue Consultancy Limited | Professional & scientific | 2011 |
| Orange Monkey Puzzle | Other services | 2019 |
| Orange Monkey Puzzle Holdings | Financial services | 2019 |
| Orbit Events Limited | Arts & recreation | 2018 |
| Orbit Production Company Limited | Administrative & support | 2025 |
| Orca Wealth Ltd | Financial services | 2016 |
| Orchard Hill Properties Limited | Real estate | 2020 |
| Orchard Manor Project Management Ltd | Construction | 2023 |
| Oria Ventures Limited | Financial services | 2026 |
| Original B.T.C. Limited | Manufacturing | 1998 |
| Original Myth Limited | Information & communication | 2013 |
| Orilian Contracting Ltd | Construction | 2026 |
| Oriri Consulting Ltd | Information & communication | 2023 |
| Orito Limited | Arts & recreation | 2014 |
| Orkla House Care UK Limited | Financial services | 2002 |
| Ormerod Rutter Accountants LLP | | 2001 |
| Orpheus Software Ventures Limited | Information & communication | 2014 |
| Orso Corporation Limited | Health & social care | 2016 |
| Ortho MSK Ltd | Health & social care | 2019 |
| Ortlinghaus UK Limited | Wholesale & retail | 1978 |
| OS Leisure Ltd | Arts & recreation | 2023 |
| Oscar Hand Carwash Ltd | Wholesale & retail | 2025 |
| Osier House Management Company Limited | Households | 2012 |
| OTB Intelligence Limited | Information & communication | 2020 |
| Otter-Av Ltd | Arts & recreation | 2025 |
| Ottolayng Limited | Households | 2023 |
| Ounje Ibile Mart Ltd | Hospitality | 2025 |
| OUR Home Style Ltd | Information & communication | 2021 |
| OUR Shooting Stars Nurseries Limited | Health & social care | 2017 |
| OUR Subs Limited | Hospitality | 2015 |
| Outbound Origins Ltd | Administrative & support | 2020 |
| Outcomes for Children (Core Assets Group) Limited | Health & social care | 2014 |
| Outcomes for Children (DN2) Limited | Health & social care | 2020 |
| Outhouse Limited | Information & communication | 2011 |
| Outlettown Limited | Wholesale & retail | 2023 |
| Outprep Ltd | Wholesale & retail | 2024 |
| Own Time and Space CIC | Health & social care | 2025 |
| Owzell Limited | Information & communication | 2020 |
| Oxferry Ltd | Other services | 2005 |
| Oxleasowes Properties Limited | Construction | 2001 |
| O’Leary Family LLP | | 2023 |
| P & H Environmental Ltd | Administrative & support | 2011 |
| P & R Technical Solutions Limited | Administrative & support | 2016 |
| P Dean Holdings Ltd | Financial services | 2023 |
| P J Hirons Limited | Construction | 2012 |
| P J Hirons Management Limited | Professional & scientific | 2003 |
| P M Z Investments Limited | Other services | 2017 |
| P Muyowa Care Ltd | Health & social care | 2018 |
| P T Williams Ceilings & Partitions Ltd | Construction | 2016 |
| P&D Surgery and Training Limited | Education | 2022 |
| P.Charles Roofing and Maintenance Ltd | Construction | 2026 |
| P.S Clothing Ltd | Wholesale & retail | 2025 |
| Pablo & Silva Limited | Wholesale & retail | 2024 |
| Pacemark Properties Limited | Construction | 1978 |
| Pacesetter Productions UK Limited | Information & communication | 2025 |
| Pada Tribe Ltd | Wholesale & retail | 2019 |
| Paddy Ray's Studio Ltd | Arts & recreation | 2025 |
| Padel DEN Ltd | Arts & recreation | 2025 |
| Paedgastro Care Limited | Health & social care | 2011 |
| Page Property and Financial Limited | Real estate | 2014 |
| Pain to Power Connect CIC | Health & social care | 2025 |