| J. D. B. Courts Limited | Construction | 2006 |
| J. F. Nott Limited | Manufacturing | 2010 |
| J. Reeves Engineering Limited | Manufacturing | 1977 |
| J.A.N. Trading Limited | Wholesale & retail | 2014 |
| J.D. Cables Limited | Wholesale & retail | 1995 |
| J.D. Flooring and Ceramics Limited | Construction | 1997 |
| J.E. Tabor (Farms) Holdings Limited | Financial services | 2012 |
| J.E.Tabor(Farms)Limited | Agriculture & fishing | 1955 |
| J.L.A. Computer Services Limited | Information & communication | 2001 |
| J.Levine Ltd | Wholesale & retail | 2023 |
| J.Mitson Building Contractors Ltd | Construction | 2017 |
| J.S & G.Hazell Ltd | Wholesale & retail | 2007 |
| J.S.R Cladding Ltd | Construction | 2026 |
| J2 Autos Ltd | Wholesale & retail | 2025 |
| JA Developments (Essex) Limited | Real estate | 1997 |
| JA Venture Limited | Health & social care | 2024 |
| Jabidorz UK Limited | Wholesale & retail | 2020 |
| Jabtl Portfolio Limited | Real estate | 2020 |
| JAC Electrical Solutions Ltd | Construction | 2026 |
| Jacana Capital Advisory Limited | Administrative & support | 2024 |
| Jackson Media Production Limited | Information & communication | 2012 |
| Jacob Smith Limited | Transport & logistics | 2024 |
| Jacommlets Limited | Construction | 2022 |
| Jade Garden Cuisine Limited | Hospitality | 2021 |
| Jade Retail Ltd | Wholesale & retail | 2020 |
| Jade Retail Services Ltd | Wholesale & retail | 2020 |
| JAG Plant Limited | Wholesale & retail | 2020 |
| Jaimin Impex Ltd | Wholesale & retail | 2025 |
| JAJ Financial Consulting Limited | Financial services | 2011 |
| Jallco Limited | Information & communication | 2014 |
| JAM 7 Creative Ltd | Professional & scientific | 2013 |
| James Godfrey Ltd | Professional & scientific | 2020 |
| James Kelly Building & Co Ltd | Construction | 2018 |
| James O'Grady Interiors Limited | Professional & scientific | 2016 |
| Jammy Apps Limited | Information & communication | 2015 |
| Janabil Property Ltd | Real estate | 2020 |
| Janice April Dewberry Limited | Extraterritorial | 2022 |
| Jank Consulting Limited | Professional & scientific | 2023 |
| Jarrow Building Developments Limited | Construction | 2005 |
| Jarvis-Williams Electrical & Data Services Limited | Energy | 2017 |
| Jashsk Ltd | Construction | 2024 |
| Jasmin Smith Limited | Administrative & support | 2024 |
| Jason Crosier Limited | Construction | 2010 |
| Jay's Refinish Limited | Wholesale & retail | 2020 |
| Jazzashley Ltd | Health & social care | 2020 |
| JB Joinery Braintree Ltd | Manufacturing | 2025 |
| JBH Sales Agencies Limited | Professional & scientific | 2010 |
| JBP Asset Management Ltd | Real estate | 2023 |
| JBR Catering Ltd | Hospitality | 2022 |
| JC Developments (Essex) Ltd | Construction | 2020 |
| JC Investments (Essex) Ltd | Construction | 2020 |
| JCK Group Ltd | Financial services | 2025 |
| JCS External Solutions Ltd | Construction | 2021 |
| Jdas Property Ltd | Real estate | 2026 |
| JDC Tech Limited | Information & communication | 2014 |
| JDJ Bryan Holdings Limited | Financial services | 2015 |
| JDS Turf Solutions Ltd | Other services | 2021 |
| JEJ Projects Limited | Information & communication | 2023 |
| Jenka Investments Ltd | Real estate | 2024 |
| Jenkins Farm Barns Common Parts Limited | Households | 2022 |
| Jenny Leonard Art Ltd | Arts & recreation | 2021 |
| Jenomax Limited | Wholesale & retail | 2010 |
| Jessica Alice Ltd | Arts & recreation | 2013 |
| JET Fuel Drip Bar Limited | Hospitality | 2024 |
| JFT Solutions Ltd | Professional & scientific | 2013 |
| Jgbaker Ltd | Administrative & support | 2019 |
| Jgjt Limited | Professional & scientific | 2026 |
| Jguk Limited | Information & communication | 2007 |
| JHB Artwork Ltd | Professional & scientific | 2021 |
| Jiggens Property Enterprises Limited | Real estate | 2020 |
| Jihenola Ltd | Real estate | 2022 |
| JIM AIM Motorcycles Limited | Wholesale & retail | 2004 |
| JJC Painting & Decorating Ltd | Construction | 2022 |
| JJM Scaffolding Ltd | Construction | 2024 |
| JK Commercial, Mechanical & GAS Engineering Solutions Limited | Energy | 2023 |
| JKB Invoice Finance Brokers Limited | Administrative & support | 2008 |
| JL777 Ltd | Real estate | 2025 |
| JLA Core Capital Ltd | Real estate | 2026 |
| JLD Business Ltd | Real estate | 2025 |
| JLR Communications Ltd | Construction | 2013 |
| JM Lawrence Fire Protection Ltd | Other services | 2013 |
| JMG Education Consultants Limited | Information & communication | 2014 |
| JMW Commercial Mentoring Ltd | Professional & scientific | 2025 |
| JNW & Co (Essex) Ltd | Professional & scientific | 2019 |
| Jofon Security Services Ltd | Administrative & support | 2025 |
| John Benson Limited | Real estate | 2004 |
| John Benson Property Limited | Real estate | 2018 |
| John E Transpor Ltd | Transport & logistics | 2025 |
| John Loader (Wessex) Limited | Manufacturing | 1998 |
| John Worsfold Limited | Agriculture & fishing | 1965 |
| Jolly Rider Limited | Transport & logistics | 2026 |
| Jonathan Bond Educational Consultancy Limited | Education | 2014 |
| Jones Electrical Installations Ltd | Construction | 2023 |
| Jones Howard Limited | Professional & scientific | 2009 |
| Jonning Limited | Other services | 2013 |
| Jono Consulting Limited | Financial services | 2020 |
| Jordbex Co. Limited | Construction | 2020 |
| JPB Global Trading Limited | Wholesale & retail | 2026 |
| JPC Accounting Services Limited | Professional & scientific | 2001 |
| JPJ Events Limited | Hospitality | 2016 |