| J Quince Electrical Ltd | Construction | 2024 |
| J V F Ltd | Hospitality | 2011 |
| J W Plumbing Ltd | Construction | 2015 |
| J Z Storage Ltd | Transport & logistics | 2025 |
| J&H Scaffolding Services Ltd | Construction | 2025 |
| J&S Brothers Property Essex Ltd | Real estate | 2026 |
| J&S Property Essex Ltd | Real estate | 2024 |
| J. S. Air CON Limited | Construction | 2003 |
| J.C Property Care Ltd | Construction | 2025 |
| J2LABS Group Ltd | Information & communication | 2025 |
| JA Social Suite Limited | Other services | 2022 |
| Jacques & Associates Limited | Professional & scientific | 1993 |
| James Fraser Gardens Ltd | Administrative & support | 2024 |
| James Gray Homes Limited | Construction | 2017 |
| Jane DOE Limited | Hospitality | 2020 |
| Jane’S Emporium Ltd | Wholesale & retail | 2024 |
| Jara Construction Limited | Construction | 2023 |
| Jasink Holdings Limited | Other services | 2019 |
| Jasire Healthcare Ltd | Wholesale & retail | 2023 |
| Jaxons Smoke & Spice Ltd. | Hospitality | 2026 |
| Jay&Son Motors Ltd | Wholesale & retail | 2024 |
| Jaywick Barbers Ltd | Other services | 2025 |
| Jaywick Community Energy and Transport CIC | Transport & logistics | 2026 |
| Jaywick Inn Limited | Hospitality | 2025 |
| Jaywick Property Limited | Real estate | 2021 |
| Jaywick Sands Revival Community Interest Company | Construction | 2018 |
| Jaywick Silicon Beach CIC | Professional & scientific | 2026 |
| JB Golf Coaching Ltd | Education | 2024 |
| JB Transport Ltd | Transport & logistics | 2011 |
| JB UK Property Ltd | Households | 2019 |
| JBJ Associates Group Limited | Professional & scientific | 2025 |
| JBJ Associates Limited | Professional & scientific | 2004 |
| JBJ Eco TEK UK Ltd | Professional & scientific | 2023 |
| JBJ Hydro TEC UK Ltd | Professional & scientific | 2023 |
| JBJ Innovation Limited | Administrative & support | 2023 |
| JBJ Projects Limited | Professional & scientific | 2021 |
| JBV Assets Limited | Arts & recreation | 2026 |
| JC Scaffold Inspections Ltd | Extraterritorial | 2024 |
| JCE Developments Limited | Construction | 2025 |
| JCO Healthcare Ltd | Administrative & support | 2025 |
| JDN Motors Limited | Wholesale & retail | 2021 |
| JEG Moves Ltd | Real estate | 2024 |
| Jennys Resource Centre Ltd | Health & social care | 2005 |
| Jensen Owners' Club Limited | Arts & recreation | 2025 |
| Jessica's Place Ltd | Hospitality | 2023 |
| JGW Maintenance Limited | Construction | 2025 |
| JHD Construction (Essex) Ltd | Construction | 2025 |
| Jim’S Transport Ltd | Transport & logistics | 2025 |
| JJ Supermarket Ltd | Hospitality | 2016 |
| JMR Building Services Limited | Construction | 2019 |
| JMS Developments & Lettings Ltd | Real estate | 2023 |
| JNB Online Ltd | Wholesale & retail | 2021 |
| JNS Care Service Limited | Health & social care | 2025 |
| JOB Exchange Limited | Financial services | 2022 |
| JOE John Watson Limited | Construction | 2026 |
| John Crawford Window Cleaning Ltd | Administrative & support | 2011 |
| John Massey U.K. Limited | Wholesale & retail | 1999 |
| Johnny Macs (Colchester) Limited | Other services | 2019 |
| Join the Gaggle Limited | Information & communication | 2021 |
| Joir Jewels Ltd | Wholesale & retail | 2023 |
| Jonathan Saffari Limited | Professional & scientific | 2014 |
| Jordan Ashley Coaching Limited | Education | 2026 |
| JQ Fulfilment Solutions Limited | Administrative & support | 2022 |
| Jred 605 Limited | Transport & logistics | 2016 |
| JS Sound Limited | Administrative & support | 2022 |
| JS Waste Ltd | Other services | 2019 |
| JSB Craftsman Ltd | Manufacturing | 2025 |
| JSD Construction Services Ltd | Real estate | 2016 |
| JSD Property (Essex) Ltd | Real estate | 2021 |
| Jsel Mortgages Ltd | Financial services | 2025 |
| Jspm Global UK Ltd | Construction | 2024 |
| JSR Flooring Limited | Construction | 2016 |
| JTN Diesel Ltd | Professional & scientific | 2024 |
| Julia Smith Ltd | Education | 2018 |
| JUN Flat Roofing Limited | Construction | 2014 |
| K M C Design Limited | Professional & scientific | 2006 |
| K Nail Ltd | Other services | 2015 |
| K Touzni Roofing Limited | Construction | 2021 |
| K1 Tech Care Ltd | Wholesale & retail | 2023 |
| Kadl Property Partners Ltd | Real estate | 2025 |
| Kalar a Ltd | Other services | 2022 |
| Kandi House Limited | Real estate | 2018 |
| Kaplan SAL Limited | Real estate | 2017 |
| Karuppu Stores Limited | Wholesale & retail | 2022 |
| Katie Dowse Finance Limited | Financial services | 2013 |
| Kaveh Group Ltd | Wholesale & retail | 2023 |
| KBM Pipe Solutions Ltd | Construction | 2018 |
| Kcbt Limited | Financial services | 2025 |
| KDD Properties Limited | Real estate | 2025 |
| KDS Contracts Ltd | Construction | 2020 |
| KEA Convenience Store Ltd | Wholesale & retail | 2024 |
| Keepsafe Enterprises Limited | Real estate | 1988 |
| Keig Ltd | Hospitality | 2024 |
| Kem's Construction Limited | Construction | 2025 |
| KEN Muir Retail Ltd | Wholesale & retail | 2010 |
| Kent Business Consultancy Ltd | Administrative & support | 2005 |
| Key Terrain Group Ltd | Administrative & support | 2016 |
| KF Laser Ltd | Manufacturing | 2022 |
| Kickback HQ Limited | Hospitality | 2024 |
| Kildens Ltd | Professional & scientific | 2018 |