| Omni Tutors Limited | Education | 2019 |
| Omnicore Energy Ltd | Construction | 2026 |
| Omnipure Ltd | Administrative & support | 2024 |
| ON the Cake Front Ltd | Wholesale & retail | 2016 |
| Once in a Lifetime Holidays Ltd | Administrative & support | 2019 |
| Oncosem UK Limited | Manufacturing | 2022 |
| One Love One Size Ltd | Wholesale & retail | 2024 |
| Onefix Builders Ltd | Administrative & support | 2016 |
| Onewaystore.Uk Ltd | Wholesale & retail | 2025 |
| Ongar Road Limited | Households | 2002 |
| ONJ Sushi Great Notley Limited | Hospitality | 2026 |
| Only Vans A12 Ltd | Wholesale & retail | 2021 |
| Onslow Financial Ltd | Professional & scientific | 2023 |
| Opal Communications Limited | Information & communication | 1996 |
| Openwavenetworks Ltd | Information & communication | 2026 |
| Optilux Design Ltd | Professional & scientific | 2024 |
| Optimus People Limited | Professional & scientific | 2012 |
| Oreon Limited | Manufacturing | 2008 |
| Organized (Essex) Limited | Other services | 2016 |
| Orion Alloys Holdings Limited | Financial services | 2024 |
| Orion Alloys Limited | Wholesale & retail | 1998 |
| Orion Business Consultancy Limited | Professional & scientific | 2012 |
| Orista Capital Ltd | Professional & scientific | 2019 |
| Orista Ltd | Information & communication | 2006 |
| Orlux Creative LLP | | 2025 |
| Orme Customs Limited | Manufacturing | 2014 |
| Oroz Ltd | Real estate | 2026 |
| ORR Financial Services Limited | Professional & scientific | 2016 |
| Orthogonal Partners LLP | | 2006 |
| Osprey Performance Ltd | Wholesale & retail | 2020 |
| Osprey Performance Media Ltd | Information & communication | 2022 |
| Osprey Performance Racing Limited | Arts & recreation | 2024 |
| Ostrich Aviation Limited | Administrative & support | 2004 |
| Otee Limited | Health & social care | 2019 |
| OUR Braintree Ltd | Professional & scientific | 2025 |
| OUR Plumber & Heating Limited | Construction | 2010 |
| Outcomtix Limited | Information & communication | 2026 |
| Outsystems Limited | Information & communication | 2013 |
| Overgoal Limited | Professional & scientific | 2004 |
| Overlook Properties Limited | Real estate | 2024 |
| Overseas Contract Purchasing Limited | Wholesale & retail | 2005 |
| Oversee Matters Ltd | Professional & scientific | 2017 |
| Ovidiu Transport Limited | Construction | 2015 |
| Ovodan EGG Products UK Limited | Wholesale & retail | 2002 |
| Owen Oppenheimer Films Limited | Information & communication | 2014 |
| Owls Hall Environmental Limited | Construction | 2002 |
| Owls Hall Farm Limited | Agriculture & fishing | 2002 |
| Oysters Capontes Limited | Hospitality | 2023 |
| Ozar & Ozar Ltd | Real estate | 2023 |
| P & a Services (Essex) Limited | Financial services | 2015 |
| P & K Leisure Ltd | Hospitality | 2014 |
| P J Sewell Limited | Other services | 1998 |
| P K Donovan Plastering Specialists Limited | Construction | 2014 |
| P N Murphy Services Ltd | Professional & scientific | 2021 |
| P&C Project Controls Ltd | Construction | 2025 |
| P. L. Maintenance Services Limited | Wholesale & retail | 2002 |
| P. Reid GAS & Heating Ltd | Construction | 2007 |
| P.A Taylor Electrical Contractors Limited | Construction | 2005 |
| P.A.F.G. Limited | Other services | 2007 |
| P.B. Interiors (Lift Industry) Limited | Manufacturing | 2008 |
| P.G. Bones Developments Ltd. | Construction | 1984 |
| P.G. Bones Limited | Construction | 1974 |
| P.H. Wheaton & Co. (Farms) Limited | Agriculture & fishing | 1974 |
| PAD Investments and Holdings Limited | Financial services | 2023 |
| PAD Technology Limited | Manufacturing | 2012 |
| Padel Essex Ltd | Arts & recreation | 2024 |
| Pallen-Mills Property and Services Ltd | Real estate | 2020 |
| Palm Tree Pools Ltd | Other services | 2001 |
| Palmer Recruitment Ltd | Administrative & support | 2025 |
| Palmtrees Dining Ltd | Hospitality | 2023 |
| Panfield Limited | Construction | 2025 |
| Panther Entertainment Limited | Information & communication | 2024 |
| PAP Security Ltd | Administrative & support | 2025 |
| Pareto Recruitment Ltd | Administrative & support | 2025 |
| Pareto Sales Management Ltd | Professional & scientific | 2024 |
| Parfait Visage Limited | Other services | 2011 |
| Parker B Associates Limited | Administrative & support | 2017 |
| Parker Styles Limited | Information & communication | 2015 |
| Parouge Ltd | Manufacturing | 2025 |
| Parpaneata Ltd | Hospitality | 2024 |
| Parrish and Hoste Building Contractors Ltd | Construction | 2025 |
| Parsloe Road Management Limited | Households | 1987 |
| Part Worn Tyres Braintree Ltd | Wholesale & retail | 2020 |
| Parthenope Properties Ltd | Real estate | 2026 |
| Party Inspirations Ltd | Wholesale & retail | 2018 |
| Passion Fruit Tree Ltd | Arts & recreation | 2017 |
| Passion Nails Ltd | Other services | 2026 |
| Passionate Catering Limited | Hospitality | 2011 |
| Patay & Co Ltd | Real estate | 2019 |
| Path Commercial Consultancy Limited | Professional & scientific | 2020 |
| Paul Cars Ltd | Wholesale & retail | 2022 |
| Paul Evans Construction Limited | Construction | 2022 |
| Paul London Limited | Manufacturing | 2014 |
| Paul Ogburn Consultancy Ltd | Professional & scientific | 2020 |
| Pauls Farm 2025 Limited | Transport & logistics | 2025 |
| Pavsv Construction Ltd | Construction | 2022 |
| PAW Services Ltd | Administrative & support | 2025 |
| PB Electrical & Maintenance Limited | Construction | 2023 |
| Pblb Healthcare Ltd | Health & social care | 2023 |
| Pblb Limited | Wholesale & retail | 2020 |