| Oilquick Investments Ltd | Agriculture & fishing | 2013 |
| OKE Consulting Limited | Professional & scientific | 2026 |
| Okoma Limited | Information & communication | 2006 |
| Old Mill Bexley Management Company Limited | Real estate | 2006 |
| Old Mill Road Limited | Real estate | 2019 |
| Olivanna Ltd | Construction | 1997 |
| Olive Bay Developments Limited | Administrative & support | 2020 |
| Olive Communications Technologies Ltd | Wholesale & retail | 2020 |
| Oliver Brobyn Limited | Administrative & support | 2019 |
| Oliverajsmith Limited | Professional & scientific | 2018 |
| Olympic Signs Limited | Manufacturing | 1994 |
| OM Saivinayak Limited | Real estate | 2011 |
| Omdm Ltd | Water & waste | 2023 |
| Omega DOT Ltd | Professional & scientific | 2016 |
| Omega Legacy Ltd | Real estate | 2023 |
| Omega Sportz Ltd | Education | 2021 |
| Omega Vend Ltd | Wholesale & retail | 2024 |
| Omigie Design Limited | Information & communication | 2011 |
| OMO R EDO Ltd | Construction | 2017 |
| ON Air Sound Design Ltd | Information & communication | 2008 |
| ON Place Ltd | Professional & scientific | 2020 |
| ON the Hill Records Limited | Wholesale & retail | 2020 |
| On-Board Production Services Limited | Information & communication | 2021 |
| One Carlton Road Freehold Company Limited | Households | 2014 |
| One DHK (UK) Ltd | Real estate | 2018 |
| One EYE on Consulting Limited | Information & communication | 2017 |
| One Giant Leap Consultancy Ltd | Information & communication | 2023 |
| One Healing Ltd | Health & social care | 2025 |
| One SJK (UK) Ltd | Real estate | 2016 |
| One Stop Contractors Ltd. | Construction | 2004 |
| One Stop Dentures Ltd | Health & social care | 2007 |
| One TON Productions Limited | Information & communication | 2015 |
| Onelift Limited | Manufacturing | 2008 |
| Onesixsix Velo Ltd | Administrative & support | 2021 |
| Onileva Limited | Information & communication | 2017 |
| Only 1 Productions Ltd. | Arts & recreation | 2002 |
| Only I CAN Ltd | Professional & scientific | 2019 |
| Only WE CAN Ltd | Professional & scientific | 2019 |
| Onpageone.Global Ltd | Administrative & support | 2024 |
| Onpoint Mechanical Services Ltd | Other services | 2017 |
| Onpointe Pilates Limited | Arts & recreation | 2019 |
| Onyx Visuals Ltd | Manufacturing | 2019 |
| Operating and Development Limited | Information & communication | 2018 |
| Operating Financial Systems Limited | Administrative & support | 2018 |
| Operating Staff Solutions Limited | Administrative & support | 2018 |
| Operating Your Brand Limited | Professional & scientific | 2018 |
| Ophthalmic Surgeons London Limited | Administrative & support | 2022 |
| OPL Commissioning Services Limited | Professional & scientific | 2020 |
| Optimal Contracts Ltd | Administrative & support | 2024 |
| Optimum Finance London Limited | Professional & scientific | 2020 |
| Optimus Sound Ltd | Information & communication | 2026 |
| Orchard Oak Projects Limited | Administrative & support | 2015 |
| Orchard Tiling Limited | Construction | 2017 |
| Original Style Tiling Ltd | Construction | 2015 |
| Orion Asset Services Limited | Real estate | 2009 |
| Orion Capital Solutions Ltd | Real estate | 2012 |
| OS Renovations Ltd | Construction | 2023 |
| Osage Dynasty Properties Limited | Real estate | 2023 |
| Oswestry Estate Management Ltd | Households | 2022 |
| Oswestry Holdings Ltd | Real estate | 2020 |
| Oswestry Property Holdings Ltd | Real estate | 2022 |
| Oswestry Property Investment Holdings Ltd | Real estate | 2022 |
| Osyntec Ltd | Information & communication | 2026 |
| OTD Catering Services Ltd | Hospitality | 2024 |
| Otherness Ltd | Arts & recreation | 2018 |
| OTP Holidays Ltd | Administrative & support | 2000 |
| Otta INK Ltd | Arts & recreation | 2025 |
| OUT Build Group Limited | Construction | 2021 |
| OUT Design Limited | Administrative & support | 2011 |
| OUT of Place Theatre Ltd | Arts & recreation | 2026 |
| OUT the FOX Limited | Information & communication | 2023 |
| Oval Commercial Domestic Limited | Construction | 2023 |
| Oval Deli Limited | Hospitality | 2023 |
| Oval DRY Cleaners (Sidcup) Limited | Other services | 2024 |
| Oval Locksmith and Security Ltd | Other services | 2023 |
| Oval Property Ltd | Real estate | 2023 |
| Oval Sidcup Cleaners Limited | Other services | 2019 |
| Overal Beauty Ltd | Other services | 2019 |
| OWL2 Ltd | Professional & scientific | 2012 |
| OWS Management Consultancy Limited | Professional & scientific | 2023 |
| Oxford Resolution Centre Limited | Professional & scientific | 2016 |
| Oxford Virtual Learning Limited | Professional & scientific | 2019 |
| OZ Schoolwear Limited | Extraterritorial | 2014 |
| Ozya Limited | Wholesale & retail | 2022 |
| P & a Carpentry and Joinery Ltd | Construction | 2013 |
| P & a Catering Services Ltd | Hospitality | 2025 |
| P & a Real Estates Ltd | Real estate | 2016 |
| P & R Drywall Limited | Construction | 2010 |
| P and E Walsh Family Ventures Limited | Financial services | 2026 |
| P Beadle Construction Limited | Construction | 2020 |
| P D Floor Limited | Wholesale & retail | 2024 |
| P O'Callaghan Services Limited | Construction | 1998 |
| P R S Scaffolding Limited | Construction | 2019 |
| P&F Logistics Limited | Construction | 2023 |
| P&G Refubishments & Maintenance Ltd | Construction | 2022 |
| P&N Utilities Limited | Construction | 2022 |
| P. & H. Building Services Ltd | Construction | 2015 |
| P.Gillibrand Consultancy Ltd. | Professional & scientific | 2016 |
| P.J. Harte (Decorating Contractors) Limited | Construction | 2004 |
| P.R. Kemp Services Limited | Construction | 2024 |