| JD Property Partners Limited | Real estate | 2025 |
| Jdks Tyre Solutions Ltd | Wholesale & retail | 2024 |
| Jdps Smiles Ltd | Health & social care | 2024 |
| Jefferies Essex LLP | | 2006 |
| Jeffs Group Services Ltd | Construction | 2026 |
| Jemac Limited | Professional & scientific | 2013 |
| Jems Finance Limited | Professional & scientific | 2013 |
| Jesco Metals Ltd | Administrative & support | 2022 |
| Jesko Consulting Ltd | Construction | 2025 |
| Jess Fit Plus Coaching Limited | Arts & recreation | 2026 |
| Jessica &Emily Limited | Hospitality | 2024 |
| Jeweltask Ltd | Information & communication | 2025 |
| JF TEZ Limited | Wholesale & retail | 2014 |
| JFH Construction Limited | Construction | 2005 |
| JHM UK Management Ltd | Professional & scientific | 2022 |
| Jics Group Limited | Professional & scientific | 2023 |
| Jigger Cocktails Limited | Manufacturing | 2021 |
| Jireh Care & Support Ltd | Health & social care | 2020 |
| JJ Building Services Consultants Ltd | Professional & scientific | 2015 |
| JJ Domestics Essex Ltd | Other services | 2026 |
| JJR Event Planning Ltd | Other services | 2023 |
| JK (Caring Carers) Limited | Health & social care | 2012 |
| JK Property Services Essex Ltd | Administrative & support | 2024 |
| JL Labs Ltd | Information & communication | 2026 |
| JL Silk Limited | Financial services | 2017 |
| JLA Construction Recruitment Limited | Administrative & support | 2025 |
| JLD Recruitment Limited | Administrative & support | 2012 |
| Jlhouse Limited | Real estate | 2026 |
| JLT Commerce Ltd | Wholesale & retail | 2023 |
| JM FOX Contracting Ltd | Professional & scientific | 2024 |
| JMI Property Investments Ltd | Real estate | 2017 |
| JMM Mortgages Ltd | Financial services | 2022 |
| Jmore Ltd | Wholesale & retail | 2022 |
| JO Barden Design Limited | Professional & scientific | 2021 |
| JO JO Developments Limited | Construction | 2015 |
| Joanne B Events Ltd | Hospitality | 2020 |
| Jodasab Limited | Health & social care | 2023 |
| Jogana Ltd | Administrative & support | 2017 |
| Johar Care Homes Limited | Health & social care | 2007 |
| John 2017 Ltd | Water & waste | 2018 |
| John COX Plastering Ltd | Construction | 2025 |
| John's Blinds Limited | Manufacturing | 2008 |
| Johnson IT Limited | Information & communication | 2007 |
| JON Horton Financial Limited | Administrative & support | 2013 |
| Jonell Steel Erectors Limited | Wholesale & retail | 1988 |
| Jordan Taylor Developments Limited | Construction | 2014 |
| Jostone Limited | Health & social care | 2023 |
| Joy Creative (Sales & Marketing) Limited | Professional & scientific | 2014 |
| JPT Education Limited | Education | 2015 |
| JR Performance Ltd | Arts & recreation | 2015 |
| JRB Aviation Limited | Manufacturing | 1976 |
| Jron Ltd | Professional & scientific | 2014 |
| JRS Construction Security Services Limited | Construction | 2013 |
| JS Homes (Wimborne) Ltd | Real estate | 2025 |
| JSB Project Consultants Limited | Professional & scientific | 2016 |
| JSD Essex Limited | Administrative & support | 2009 |
| JSG Metering Solutions Ltd | Manufacturing | 2013 |
| JT Nails Limited | Other services | 2005 |
| JT1 Property Limited | Real estate | 2024 |
| JTG Surveying Services Ltd | Professional & scientific | 2022 |
| JTP Mechanical Engineering Limited | Professional & scientific | 2016 |
| JTS Properties (London) Ltd | Real estate | 2021 |
| Jubilee Medical Services Ltd | Health & social care | 2022 |
| Judith ANN Court Management Limited | Households | 1995 |
| Juji Ltd | Professional & scientific | 2016 |
| Jules Stenson Media Limited | Professional & scientific | 2017 |
| Julia Oaksford Ltd | Professional & scientific | 2013 |
| Julia Tiffin's Practice Ltd | Other services | 2021 |
| Julian Transport Ltd | Transport & logistics | 2013 |
| Juma Consultancy Limited | Administrative & support | 2025 |
| Jupiter Trading Limited | Real estate | 2002 |
| Jury Financial Solutions Limited | Financial services | 2023 |
| Just ADD Salt Ltd | Administrative & support | 2025 |
| Just Comic Books Ltd | Wholesale & retail | 2026 |
| Just Control Limited | Professional & scientific | 2018 |
| Just Relocate Ltd | Real estate | 2020 |
| Jvmn Ltd | Extraterritorial | 2022 |
| JVT Lettings Limited | Real estate | 2026 |
| K & S Pipe Contractors LLP | | 2003 |
| K Newson KN Therapy Ltd | Health & social care | 2025 |
| K R H Contracts Limited | Construction | 2013 |
| K R Heating and Plumbing Limited | Construction | 2019 |
| K&A Executives Limited | Administrative & support | 2024 |
| K&E Drylining Ltd | Construction | 2015 |
| K&J Grunt Ltd | Real estate | 2025 |
| K. & K. Scaffolding Limited | Construction | 1996 |
| K.A.B. Installations Limited | Construction | 1998 |
| K.R. Berry Limited | Construction | 1999 |
| K.W. Hadleigh Limited | Construction | 1965 |
| K16 Construction Ltd | Construction | 2012 |
| Kadilsa Services Ltd | Wholesale & retail | 2026 |
| Kafmed Ltd | Health & social care | 2011 |
| Kaili Limited | Hospitality | 2021 |
| Kaje & Jess Ltd | Real estate | 2023 |
| Kaleidoscope (Tylers) Management Company Limited | Households | 2015 |
| KALI2 Limited | Real estate | 2024 |
| Kallathumangalath Ltd | Health & social care | 2024 |
| Kallos Collective Ltd | Other services | 2026 |
| Kalm Beauty Ltd | Other services | 2023 |
| Kalm Design Ltd | Professional & scientific | 2019 |