| Invicta Essex Limited | Real estate | 2021 |
| Invitation Homes Limited | Extraterritorial | 2012 |
| Invogue Styling Limited | Wholesale & retail | 2016 |
| Ipsum Consultancy Services Limited | Professional & scientific | 2019 |
| Iris Consultants Limited | Information & communication | 2018 |
| Iris Fawns Limited | Financial services | 2021 |
| Iris Insurance Brokers Limited | Financial services | 2000 |
| Iris M & K Limited | Financial services | 2012 |
| Iris Property Holdings Limited | Real estate | 2020 |
| Iris Toys Limited | Arts & recreation | 2020 |
| IRM Estates Ltd | Real estate | 2019 |
| Iron Lake Balls Ltd | Wholesale & retail | 2022 |
| Ironman Robotics Ltd | Manufacturing | 2010 |
| IS Shopping Ltd | Wholesale & retail | 2026 |
| ISA Sports and Wellbeing Limited | Education | 2020 |
| Isalga Aviation Advisor Limited | Professional & scientific | 2021 |
| Isfield Farms (Regis) Limited | Extraterritorial | 2003 |
| ISH Physiotherapy Ltd | Health & social care | 2024 |
| Isle & Eagle Limited | Construction | 2019 |
| Isles Global Solutions Limited | Wholesale & retail | 2025 |
| Ispy Services Limited | Administrative & support | 2017 |
| Issana Cleaning Services Ltd | Administrative & support | 2025 |
| IT & Media Solutions Ltd | Information & communication | 2001 |
| Itax Solutions Ltd | Professional & scientific | 2019 |
| ITB Developments Ltd | Construction | 2023 |
| IVP Airspace Limited | Real estate | 2022 |
| Izmir Doner Kebab Ltd | Hospitality | 2022 |
| Izod and Burnip Limited | Wholesale & retail | 1962 |
| Izzy-Meds Ltd | Wholesale & retail | 2021 |
| J & a Landscapes & Plant Hire Limited | Construction | 2025 |
| J & J Holdings & Investments Ltd | Wholesale & retail | 2024 |
| J & M Plumbing & Heating Limited | Construction | 2017 |
| J & N Guest Holdings Limited | Financial services | 2017 |
| J B Dean Construction Ltd | Construction | 2025 |
| J Bates Services Limited | Manufacturing | 2005 |
| J Graff Productions Ltd | Administrative & support | 2025 |
| J Grant Rigging Limited | Construction | 2025 |
| J J Management Consulting LLP | | 2011 |
| J J R Utilities Limited | Energy | 2024 |
| J Jacques Ltd | Manufacturing | 2017 |
| J M Air Services Ltd | Construction | 2018 |
| J M O Rheumatology Limited | Health & social care | 2019 |
| J Marshall Building Services Limited | Construction | 2002 |
| J Mathews Consultancy Ltd | Professional & scientific | 2024 |
| J P Lalmer Limited | Professional & scientific | 2015 |
| J Williams Decorators Limited | Construction | 2012 |
| J&A Tiling Contractors Ltd | Construction | 2012 |
| J. D. B. Futures Limited | Financial services | 2017 |
| J. Hayden & Sons Ltd | Construction | 2015 |
| J. Kaley Associates Limited | Arts & recreation | 1982 |
| J. Noble Butchers Limited | Wholesale & retail | 2014 |
| J.B.H. Plumbing & Heating Limited | Construction | 2011 |
| J.Braham Everett Imports Ltd | Wholesale & retail | 2013 |
| J.Braham Everett Shipping Ltd | Transport & logistics | 2020 |
| J.C. Consultancy Essex Limited | Construction | 2015 |
| J.H. Rawley Group Limited | Professional & scientific | 1963 |
| J.Lee & Co(Southend)Limited | Wholesale & retail | 1957 |
| J.S.M. Automotive Surfacing Ltd | Professional & scientific | 2014 |
| J.W.Janes & Company Limited | Manufacturing | 1939 |
| J.Zee.Tech Ltd | Wholesale & retail | 2020 |
| J4 Ventures Limited | Real estate | 2025 |
| JA Squared Properties Ltd | Real estate | 2024 |
| Jaaatt Engineering Limited | Manufacturing | 2020 |
| Jabal Al-Nour Ltd | Real estate | 2024 |
| Jabiha Traders Limited | Wholesale & retail | 2025 |
| Jacksons Property Ltd | Real estate | 2021 |
| Jacobs of Southend Ltd | Wholesale & retail | 2021 |
| Jadeamy Boutique Ltd | Wholesale & retail | 2022 |
| Jaeger Security Ltd | Administrative & support | 2024 |
| Jalalabad Associates Limited | Wholesale & retail | 2025 |
| JAM Wealth Consultants Limited | Financial services | 2018 |
| James & the Giant Bean Limited | Wholesale & retail | 2024 |
| James Associates London Limited | Real estate | 1999 |
| James Gibb and Co. Limited | Wholesale & retail | 1984 |
| James Heys & Sons Limited | Other services | 1965 |
| Jancave Developments Limited | Construction | 1997 |
| Janeva Investments Ltd | Real estate | 2019 |
| Jaro Signs (Holdings) Ltd | Financial services | 2004 |
| Jaro Signs Limited | Manufacturing | 1982 |
| Jashmalyn Limited | Health & social care | 2021 |
| Jasmine Day Spa Limited | Other services | 2022 |
| Jasmine Park Residents Management Company Limited | Households | 2019 |
| Jasmine Photography Limited | Professional & scientific | 2010 |
| Jason Keith Jewellery Limited | Manufacturing | 2013 |
| Jato Security Services Limited | Administrative & support | 2016 |
| JAY UK Services Ltd | Real estate | 2026 |
| Jayco International Forwarding Limited | Transport & logistics | 1997 |
| Jaytrackventures Limited | Health & social care | 2020 |
| Jaywick Developments Ltd | Real estate | 2017 |
| Jazzco 1967 Ltd | Wholesale & retail | 2002 |
| JBB Aviation Ltd | Manufacturing | 2013 |
| JBR Transport Ltd | Construction | 2017 |
| JBW3768 Limited | Other services | 2025 |
| JC Consultant Ltd | Professional & scientific | 2026 |
| JC Sneakers Limited | Wholesale & retail | 2020 |
| JCA Plumbing & Heating Merchants Ltd | Wholesale & retail | 2011 |
| JD Development & Carpentry Limited | Construction | 2017 |
| JD Fabrication and Welding Ltd | Manufacturing | 2017 |
| JD Farriers Ltd | Agriculture & fishing | 2025 |
| JD Investing Ltd | Financial services | 2023 |