| Omron Limited | Wholesale & retail | 2015 |
| Omron Management Ltd | Real estate | 2017 |
| ONA365 Ltd | Administrative & support | 2021 |
| Onaci Ltd | Construction | 2017 |
| Oncoflux Limited | Information & communication | 2026 |
| Ondycz Tech Services Ltd | Professional & scientific | 2025 |
| One 3 Four Life Limited | Hospitality | 2018 |
| One Cossington Road Limited | Other services | 1995 |
| One World Group Corporation Ltd | Professional & scientific | 2025 |
| Oneclick Business Services Ltd | Professional & scientific | 2017 |
| Onehub Offices Ltd | Real estate | 2026 |
| Onell Ltd | Administrative & support | 2015 |
| Onestopbadges Ltd | Manufacturing | 2012 |
| Onshore Leasehold Accountancy Ltd | Professional & scientific | 2013 |
| Ontrad Limited | Wholesale & retail | 2012 |
| Onyx Cornerstone Ltd | Health & social care | 2020 |
| Oolala Sushi Ltd | Hospitality | 2022 |
| Opakitchen Limited | Hospitality | 2025 |
| Opantha Ltd | Health & social care | 2019 |
| Open JAR Solutions Ltd | Construction | 2024 |
| Open to Close Limited | Other services | 2025 |
| Opendoor Properties Limited | Real estate | 1996 |
| Optilite International Limited | Information & communication | 2016 |
| Optimal Roofing Solutions Ltd | Construction | 2019 |
| Optimised Nutrition Ltd | Wholesale & retail | 2025 |
| OPTIMIZE10 Limited | Professional & scientific | 2023 |
| Optimum Time Limited | Wholesale & retail | 2004 |
| Opus Commercial Solutions Ltd | Financial services | 2020 |
| Opus Finance Group Ltd | Financial services | 2016 |
| ORA365 Ltd | Administrative & support | 2021 |
| Oracle Publications (UK) Limited | Information & communication | 2008 |
| Orbient Global Ltd | Information & communication | 2025 |
| Orbital Comfy Homes Limited | Real estate | 2023 |
| Orchid Print Limited | Information & communication | 2003 |
| Ordanics Ltd | Other services | 2024 |
| Organic Consulting Ltd | Administrative & support | 2016 |
| Orial System Solutions Limited | Information & communication | 2024 |
| Original Automotive Ltd | Wholesale & retail | 2017 |
| Original Sports Limited | Wholesale & retail | 2020 |
| Orion Court (Basildon) Management Company Limited | Real estate | 1984 |
| Orions Enterprises Ltd Ltd | Wholesale & retail | 2019 |
| Orko Electrical Ltd | Manufacturing | 2020 |
| Orosei Limited | Health & social care | 2011 |
| Orsuta Limited | Health & social care | 2013 |
| Ortho Power Repairs Ltd | Manufacturing | 2020 |
| Osborne Rail Ltd | Manufacturing | 2018 |
| Osbourne House Management Company (Westcliff-On-Sea) Limited | Real estate | 1996 |
| Oscar James Partners Ltd | Professional & scientific | 2020 |
| Osprey Rise (Peters Village) Management Company Limited | Households | 2020 |
| Ospringe Gardens (Faversham) Management Company Limited | Households | 2020 |
| OSR Tech Holdings Ltd | Information & communication | 2026 |
| Otech Fire Limited | Professional & scientific | 2026 |
| OTG Utilities Ltd | Construction | 2019 |
| Oughtibridge Valley (Oughtibridge) Management Company Limited | Households | 2021 |
| OUR A25 Garage Limited | Wholesale & retail | 2018 |
| Overcliff Apartments Services Limited | Administrative & support | 1975 |
| Owen's Services Consulting Limited | Professional & scientific | 2015 |
| OWL (UK) LLP | | 2007 |
| OWL Media Ltd | Professional & scientific | 2018 |
| Own Time Studios Ltd | Information & communication | 2024 |
| Ownit Ltd | Transport & logistics | 2018 |
| Oyster Workforce Solutions Ltd | Administrative & support | 2020 |
| P & D Bond Kitchen Fitters Limited | Construction | 2012 |
| P & S Dairies Limited | Wholesale & retail | 2019 |
| P E Construction Limited | Construction | 2014 |
| P Tate Consulting Ltd | Information & communication | 2023 |
| P&G Platinum Property Ltd | Financial services | 2021 |
| P&J Billericay Ltd | Manufacturing | 2024 |
| P&J Decorating Limited | Construction | 2011 |
| P&R Service Limited | Construction | 2011 |
| P.A.K. Accountants Ltd | Professional & scientific | 2011 |
| P.T.W. Stanton Limited | Real estate | 1994 |
| P.Tomassi and SON Limited | Hospitality | 1947 |
| P1 Properties Ltd | Real estate | 2020 |
| P2G Management Limited | Professional & scientific | 2016 |
| PA Foods and Wines Limited | Wholesale & retail | 2025 |
| Pace Bport 3 Ltd | Real estate | 2019 |
| Pace Bport 4 Ltd | Real estate | 2019 |
| Pace Bport 5 Ltd | Real estate | 2019 |
| Pace Bport 7 Ltd | Real estate | 2021 |
| Pace Estate Agency Ltd | Real estate | 2005 |
| Pack Sales Limited | Professional & scientific | 2020 |
| Pack Wizards Ltd | Wholesale & retail | 2025 |
| Pagan Marketing Limited | Wholesale & retail | 1983 |
| Page Portal Ltd | Information & communication | 2013 |
| Pall Mall Living Limited | Construction | 2018 |
| Palm Raine Ltd | Wholesale & retail | 2025 |
| Palmers Jewellery Limited | Wholesale & retail | 2007 |
| Palmwave Dynamics Ltd | Information & communication | 2025 |
| Palthanio Ltd | Information & communication | 2024 |
| PAN Property Ltd | Real estate | 2018 |
| Panchal Travels Ltd | Administrative & support | 2025 |
| Paneurope Commodity Consulting Ltd | Financial services | 2017 |
| Pangea Global Limited | Wholesale & retail | 2022 |
| Panopticon Management Limited | Real estate | 2014 |
| Pansula Health Care Limited Company Ltd | Real estate | 2016 |
| Panthamax Ltd | Real estate | 2025 |
| Panthapro Ltd | Real estate | 2026 |
| Panthergas Direct Limited | Manufacturing | 2010 |
| Papa's Recycling Ltd | Wholesale & retail | 2018 |