| Joanne Vertannes Ltd | Professional & scientific | 2023 |
| Jobfusion Limited | Extraterritorial | 2009 |
| JOBG8 Limited | Information & communication | 2003 |
| Jobgate Limited | Professional & scientific | 2003 |
| Jobnet South Africa Limited | Extraterritorial | 2011 |
| Jobserve Events Ltd | Extraterritorial | 1986 |
| Jobserve Limited | Administrative & support | 1993 |
| Jobserve Sports and Social Club | Arts & recreation | 2007 |
| Jocks Ltd | Construction | 2015 |
| Jodice Care Limited | Health & social care | 2015 |
| JOE Partridge Marketing Research Limited | Professional & scientific | 2006 |
| Joeflex Global Services Ltd | Wholesale & retail | 2023 |
| Joel Business Services Ltd | Administrative & support | 2021 |
| Joesiben Limited | Health & social care | 2019 |
| Joetechav Ltd | Information & communication | 2016 |
| Joha International Ltd | Construction | 2024 |
| John Alexander Colchester Ltd | Real estate | 2013 |
| John Alexander Harwich Ltd | Real estate | 2024 |
| John Alexander Lettings Ltd | Real estate | 2023 |
| John Alexander Tiptree Ltd | Real estate | 2020 |
| John Bull Motors Limited | Wholesale & retail | 2003 |
| John Butcher Property Management Ltd | Real estate | 2026 |
| John C Building Services Limited | Construction | 2015 |
| John Carter Electrical Contractor Ltd | Construction | 2013 |
| John Daniel Properties Limited | Real estate | 2018 |
| John Dedross Surveying Limited | Professional & scientific | 2024 |
| John Entertainments Ltd | Information & communication | 2017 |
| John Fowlers LLP | | 2008 |
| John Fowlers Property (West Mersea) Ltd | Households | 2018 |
| John Fowlers Property Limited | Real estate | 2011 |
| John Martin EOT Limited | Administrative & support | 2018 |
| John Martin of London Limited | Wholesale & retail | 1946 |
| John S. Campbell & Company Limited | Real estate | 1928 |
| John Stanley's Care Agency Limited | Health & social care | 1997 |
| John Tours Ltd | Administrative & support | 2019 |
| John Waite Holdings Limited | Real estate | 2021 |
| John Warner Consulting Limited | Administrative & support | 2011 |
| John Whiting Limited | Wholesale & retail | 1968 |
| John's Fish Bar Anglian Ltd | Hospitality | 2025 |
| Johnny Roxburgh Designs Limited | Other services | 2010 |
| Johnson and Sons Colchester Ltd | Wholesale & retail | 2024 |
| Johnsons Flat Roofing Services Ltd | Construction | 2024 |
| Johnston & SON Property Ltd | Real estate | 2025 |
| Join Social Care Ltd | Administrative & support | 2023 |
| Joint Enterprises Limited | Wholesale & retail | 1999 |
| Jola Strategic Limited | Professional & scientific | 2019 |
| Jolakes Ltd | Administrative & support | 2024 |
| Jolly House RTM Company Limited | Households | 2025 |
| Jolyon Berry Limited | Financial services | 2018 |
| Jomalo Ltd | Real estate | 2026 |
| Jonathan Burton & Co. Limited | Administrative & support | 1998 |
| Jonathan Isted Coaching Ltd | Other services | 2025 |
| Jonathan Lamptey Ltd | Administrative & support | 2017 |
| Jonathan Osborne Limited | Wholesale & retail | 2009 |
| Jonathan Wise Ltd | Professional & scientific | 2014 |
| Jonathan's Bramford Ltd | Wholesale & retail | 2023 |
| Jones & Whymark Engineering Limited | Manufacturing | 1980 |
| Jones & Whymark Holdings Limited | Financial services | 2020 |
| Jones Air Conditioning Solutions Limited | Construction | 2014 |
| Jones Dooly Holdings Limited | Transport & logistics | 1997 |
| Jones Dooly Limited | Transport & logistics | 1923 |
| Jonny Stillwell Ltd | Information & communication | 2015 |
| Jopeda Ltd | Wholesale & retail | 2025 |
| Jophiel Flowers Limited | Wholesale & retail | 2025 |
| Jordan Store Ltd | Wholesale & retail | 2026 |
| Jordan's Farm Environmental Ltd | Agriculture & fishing | 2022 |
| Jordec Business Services Limited | Real estate | 2021 |
| Jordec Communications Limited | Information & communication | 2021 |
| Jordec Community Housing Ltd | Real estate | 2021 |
| Jordec International Limited | Professional & scientific | 2022 |
| Jordec Investment Group Ltd | Financial services | 2021 |
| Josa Services Limited | Real estate | 2015 |
| Joseph James Project Services Limited | Professional & scientific | 2023 |
| Josephinejamessalon Ltd | Other services | 2023 |
| Joshbel Services Ltd | Administrative & support | 2018 |
| Joshua Building Ltd | Construction | 2024 |
| Joslin Close Management Company Limited | Households | 2020 |
| José Powell Gardens Management Company Ltd | Real estate | 2024 |
| JOT London Ltd | Wholesale & retail | 2021 |
| Jouets Limited | Extraterritorial | 2017 |
| Journal of Industrial Economics (Editorial Board) Limited | Information & communication | 1986 |
| Jova Holdings Ltd | Real estate | 2022 |
| Joviprieke Ltd | Other services | 2020 |
| Jovis Limited | Construction | 2004 |
| Joy Socials Ltd | Professional & scientific | 2024 |
| Joy Trading Ltd | Wholesale & retail | 2023 |
| Joyfulspring Ltd | Health & social care | 2019 |
| Joypad Limited | Wholesale & retail | 2013 |
| JP Metals and Futures UK Limited | Other services | 2021 |
| JP Security Solutions Limited | Information & communication | 2014 |
| JP Stock Homes Ltd | Construction | 2020 |
| JP Stock Ltd | Construction | 2015 |
| JP Trades Ltd | Wholesale & retail | 2025 |
| JPB Brickwork Ltd | Construction | 2025 |
| JPB Landscapes Ltd | Administrative & support | 2020 |
| JPM Colchester Ltd | Wholesale & retail | 2021 |
| JPT Education Consultancy Limited | Professional & scientific | 2023 |
| JR 374 Electrical Ltd | Construction | 2023 |
| JR Automotive Consultancy and Training Services Ltd | Wholesale & retail | 2019 |
| JR Eley Limited | Financial services | 2024 |