| J. T Barrett Building Ltd | Construction | 2014 |
| J.E Landscapes & Paving Ltd | Administrative & support | 2026 |
| J.F. Haag & Sons (Pork) Limited | Agriculture & fishing | 1963 |
| J.F. Haag + Partners | | 1997 |
| J.G.Beauchamp Limited | Administrative & support | 2025 |
| J.J. Millgate Limited | Real estate | 1977 |
| J.J.Wilson(Ipswich)Limited | Wholesale & retail | 1933 |
| J.M.P. Services Limited | Construction | 2002 |
| J.Mattison Limited | Manufacturing | 1997 |
| J.R.J.Small Limited | Construction | 2014 |
| J.S.Tree&Garden Services Ltd | Agriculture & fishing | 2025 |
| J.T. Elvin Limited | Wholesale & retail | 1963 |
| J.T. FEW Plant Hire Ltd | Water & waste | 2002 |
| J2 Carpentry Limited | Construction | 2022 |
| J4 Resourcing Ltd | Extraterritorial | 2020 |
| J9 Properties Ltd | Real estate | 2022 |
| JA Driving Ltd. | Transport & logistics | 2019 |
| JA Farming Ltd | Agriculture & fishing | 2024 |
| JA Foods EN Limited | Hospitality | 2024 |
| Ja&J Limited | Real estate | 2025 |
| JAA Limited | Real estate | 2022 |
| Jaaj Enterprises Limited | Professional & scientific | 2017 |
| Jabrio | Financial services | 2023 |
| JACH9 Ltd | Financial services | 2017 |
| Jack Breheny Limited | Construction | 1969 |
| Jack Way (Stonham Aspal) Management Company Ltd | Real estate | 2022 |
| Jackdaw Living Limited | Wholesale & retail | 2018 |
| Jackhs Limited | Professional & scientific | 2024 |
| Jackson Civil Engineering Group Limited | Construction | 2008 |
| Jackson Place (Barham) Management Company Limited | Households | 2007 |
| Jackson Plumbing & Heating (East Anglia) Limited | Construction | 2008 |
| Jacksonhyder Limited | Financial services | 2013 |
| Jacksonville Property Ltd | Real estate | 2023 |
| Jacob Bailey Group Limited | Financial services | 2015 |
| Jacob Bailey Limited | Professional & scientific | 1998 |
| Jacobs & SON Lettings Limited | Real estate | 2018 |
| Jacobs Allen Group Limited | Professional & scientific | 2012 |
| Jacobs Allen Limited | Professional & scientific | 2012 |
| Jacobs GAS and Heating Limited | Construction | 2021 |
| Jacobs Way (Management) Limited | Households | 1997 |
| Jacques Catering Ltd | Hospitality | 2024 |
| Jaddot Family LLP | | 2024 |
| Jade and Ajay Ltd | Professional & scientific | 2024 |
| Jade Rose Limited | Other services | 2015 |
| Jade Village Ltd | Hospitality | 2016 |
| Jaemny Global Scientific Ltd | Wholesale & retail | 2026 |
| Jaferg Trading Ltd | Wholesale & retail | 2024 |
| Jaffa Tech Solutions Ltd | Information & communication | 2022 |
| Jafis Place Limited | Hospitality | 2024 |
| Jafro Limited | Information & communication | 2024 |
| JAH Medical Limited | Health & social care | 2025 |
| Jaht Management Property Solution Ltd | Real estate | 2026 |
| Jaira Restaurants Ltd | Hospitality | 2025 |
| JAK Imaging and Medical Solutions Limited | Administrative & support | 2014 |
| Jakcat Limited | Real estate | 2002 |
| Jakecon Limited | Financial services | 2008 |
| Jakeman Solar Limited | Construction | 2013 |
| Jako's Group Limited | Agriculture & fishing | 2017 |
| Jakstat Property Limited | Real estate | 2022 |
| Jam-Tek Solutions Limited | Information & communication | 2022 |
| James Alexander Consulting Services Ltd | Professional & scientific | 2021 |
| James Barr & Sons (Farmers) Limited | Agriculture & fishing | 1952 |
| James C Ward Ltd | Information & communication | 2023 |
| James Caley Ltd | Transport & logistics | 2010 |
| James Dyson Ltd | Professional & scientific | 2024 |
| James Foskett Contracts Limited | Agriculture & fishing | 2016 |
| James Foskett Farms Limited | Agriculture & fishing | 2004 |
| James Francis (Construction) Limited | Construction | 2014 |
| James Francis (Developments) Limited | Construction | 2014 |
| James Francis (Homes) Ltd | Construction | 2013 |
| James Long Ltd | Administrative & support | 2008 |
| James Mens Group Ltd | Wholesale & retail | 2024 |
| James Oates Limited | Arts & recreation | 2022 |
| James Prentice Limited | Information & communication | 2009 |
| Jamie Clarke Counselling Ltd | Health & social care | 2018 |
| Jamie Cook Ltd | Construction | 2013 |
| Jamie LEE Smith Catering @ Greshams Ltd | Hospitality | 2019 |
| Jamie LEE Smith Catering Limited | Hospitality | 2018 |
| Jamie Mouser Transport Limited | Administrative & support | 2014 |
| Jamie Rhind Ltd | Professional & scientific | 2019 |
| Jamie Rich Builders Limited | Construction | 2003 |
| Jamieson B&M Limited | Real estate | 2023 |
| Jamieson Group Ltd | Extraterritorial | 2012 |
| Jammy Beatz Ltd | Wholesale & retail | 2023 |
| Jammy Doughnuts Ltd | Hospitality | 2021 |
| JAN Merkaba Limited | Construction | 2023 |
| Jandnet Limited | Information & communication | 2001 |
| Jane Hamerton Limited | Manufacturing | 2009 |
| Jane Riley Limited | Professional & scientific | 2024 |
| Jane's Holdings Limited | Financial services | 2022 |
| Janice Rowles Ltd | Professional & scientific | 2015 |
| Janice Tildsley Associates Ltd | Arts & recreation | 2003 |
| JAO Empire Operations Limited | Wholesale & retail | 2025 |
| Japagidan Ltd | Information & communication | 2025 |
| Japs Security (Suffolk) Limited | Administrative & support | 2006 |
| Jardin Sirocco Foundation | Financial services | 2025 |
| Jaris Health Limited | Health & social care | 2024 |
| Jaro Transport Ltd | Transport & logistics | 2022 |
| Jaruma Ltd | Real estate | 2026 |
| JAS Paul Ltd | Transport & logistics | 2024 |