| ON a Reel Ltd | Information & communication | 2024 |
| ON8 Media Limited | Real estate | 2020 |
| One Marketing Limited | Professional & scientific | 2002 |
| One Step Ahead (Essex) Limited | Health & social care | 2012 |
| Onex Solutions Ltd | Information & communication | 2016 |
| ONG Investment Limited | Real estate | 2016 |
| ONG Media Group Ltd | Information & communication | 2017 |
| Onnik M Limited | Construction | 2016 |
| Onsiteit Ltd | Information & communication | 2021 |
| Onyx Electrical UK Ltd | Construction | 2026 |
| Onyx GB Limited | Construction | 2008 |
| Opemed (Europe) Limited | Wholesale & retail | 2008 |
| Open Rainbow Limited | Information & communication | 2014 |
| Opendata Consult Ltd | Information & communication | 2017 |
| Optimhm Consulting Ltd | Professional & scientific | 2025 |
| Optimise Admin Services Limited | Administrative & support | 2025 |
| Optimise IT Limited | Information & communication | 2021 |
| Opulence Property Group Ltd | Real estate | 2020 |
| Oracle Surveyors Ltd | Professional & scientific | 2022 |
| Orange Rock Management Limited | Professional & scientific | 2024 |
| Oranges & Lemons Productions UK Limited | Information & communication | 2025 |
| Orbital Accounting Services Limited | Professional & scientific | 2000 |
| Orca Investments Limited | Financial services | 2010 |
| Orchestra Agency Limited | Professional & scientific | 2007 |
| Oriental Express CM12 Ltd | Hospitality | 2026 |
| Orion Security Ltd | Administrative & support | 2025 |
| OS Utility Project Ltd | Agriculture & fishing | 2025 |
| Osborn & Clayden Property Ltd | Real estate | 2025 |
| Osborne Construction Management Ltd | Professional & scientific | 2025 |
| Oscar Fairchild (Essex) Limited | Professional & scientific | 2011 |
| Oscar Fairchild (London) Limited | Professional & scientific | 2016 |
| Osmo Partners LLP | | 2014 |
| Osmosis Technology Limited | Information & communication | 2025 |
| OUT of This Weld Limited | Manufacturing | 2022 |
| OUTSOURCE247 Ltd | Administrative & support | 2023 |
| Oval Peak Partners Ltd | Financial services | 2020 |
| Oyster Beauty Academy Limited | Education | 2019 |
| Ozed Ltd | Administrative & support | 2021 |
| Oztwo Limited | Wholesale & retail | 2006 |
| P & P Servicing Ltd | Construction | 2022 |
| P G Amps Limited | Manufacturing | 2007 |
| P H Coaching Ltd | Professional & scientific | 2022 |
| P J Mooney Limited | Construction | 2009 |
| P L D Properties Limited | Real estate | 2001 |
| P L Mcveigh Property Limited | Real estate | 2025 |
| P. Barrett Limited | Professional & scientific | 1997 |
| P.G. Wilkins Motor Engineer Limited | Wholesale & retail | 2004 |
| P.J.C.C. Services Ltd | Other services | 2020 |
| P.O. Box Shipping UK Limited | Transport & logistics | 2016 |
| P.O. Box Shopping UK Limited | Transport & logistics | 2016 |
| P.S Orton Limited | Construction | 2016 |
| Pacmicro Limited | Real estate | 1996 |
| Padel Pelota Limited | Arts & recreation | 2025 |
| Paediatric PAN London Oxygen Group (Pplog) Ltd | Other services | 2021 |
| Paheda Limited | Households | 2019 |
| Paint IT UK Ltd | Construction | 2015 |
| Paladin Private Wealth Limited | Financial services | 2013 |
| Palazzo Corfino Ltd | Professional & scientific | 2009 |
| Pali 48 Limited | Real estate | 2008 |
| Palindrome Consulting Limited | Information & communication | 2011 |
| Paling & Jenkins Ltd | Administrative & support | 2016 |
| Palm Springs Retail Limited | Wholesale & retail | 2023 |
| Palmers Building and Property Services Limited | Other services | 2025 |
| Palum Consulting Ltd | Information & communication | 2022 |
| Papa’S Bites Ltd | Hospitality | 2024 |
| Paradigm Planning & Economics Limited | Professional & scientific | 2015 |
| Parisque Limited | Wholesale & retail | 2018 |
| Park View Resourcing Ltd. | Construction | 2022 |
| Parnell Floors Limited | Construction | 2020 |
| Parsons Estates Ltd | Real estate | 2013 |
| Partitioning Services Limited | Construction | 2000 |
| Partners of Essex Anaesthetic Plexus LLP | | 2025 |
| Patesco Limited | Administrative & support | 2025 |
| Patrick Knight Investments Limited | Construction | 2007 |
| Patrick Sandberg Antiques Limited | Administrative & support | 2002 |
| Paul Catchpole Driving Ltd | Transport & logistics | 2019 |
| Paul Jamie Construction Ltd | Construction | 2018 |
| Paul Jamie Consultants Ltd | Professional & scientific | 2024 |
| Paula Churchill Training Solutions Limited | Education | 2022 |
| Pavement Production Limited | Manufacturing | 2012 |
| Pawfect Treasures Limited | Wholesale & retail | 2026 |
| Paws on Social Ltd | Information & communication | 2020 |
| Paxford Hutchinson Ltd | Construction | 2022 |
| Paye for Nannies Limited | Financial services | 2002 |
| PB Group (UK) Limited | Professional & scientific | 2013 |
| PBM Group Ltd | Construction | 2021 |
| PBM Plastics Ltd | Wholesale & retail | 2024 |
| PBR Executive Search Limited | Administrative & support | 2022 |
| PBS Holdings Limited | Other services | 2025 |
| PBS Homes Ltd | Construction | 2018 |
| Pcdepartment Limited | Other services | 2007 |
| PCM Health Technologies and Services Limited | Professional & scientific | 2021 |
| PCP Limited | Professional & scientific | 1993 |
| PDQ IT Support Limited | Information & communication | 2018 |
| Peace of Mind Trading Limited | Wholesale & retail | 2013 |
| Peaks Properties Limited | Construction | 2021 |
| Pegrum Electrical Ltd | Construction | 2024 |
| Pemlosa Limited | Wholesale & retail | 2020 |
| Penguin Products Limited | Administrative & support | 2016 |
| Penny Jane Flowers Limited | Wholesale & retail | 2012 |