| J&R Karaoke Ltd | Arts & recreation | 2023 |
| J'S Garden Valet Services Limited | Other services | 2003 |
| J-Quilts Innova Ltd | Wholesale & retail | 2021 |
| J. & J. D. Surveying Ltd | Professional & scientific | 2024 |
| J. Coleman Wholesale Butchers Limited | Manufacturing | 1979 |
| J. Gosling (Insurance Brokers) Limited | Real estate | 1972 |
| J. H. Hellen Plumbing & Heating Limited | Construction | 2009 |
| J. J. Lyrics Ltd | Construction | 2003 |
| J. Owen Limited | Professional & scientific | 1981 |
| J. Tate Construction Limited | Construction | 2007 |
| J.&S. Golden Homes Ltd | Real estate | 2025 |
| J.B.Fennell Limited | Real estate | 1964 |
| J.C. Bradshaw Building Services Limited | Construction | 2004 |
| J.D.T. (U.K.) Limited | Wholesale & retail | 1994 |
| J.G. Carpentry & Kitchens Ltd | Construction | 2013 |
| J.J. Rogers Limited | Construction | 2002 |
| J.Jackson Heating Ltd | Construction | 2024 |
| J.Parmenter Plant Services Ltd | Manufacturing | 2019 |
| J.Pearce | | 1989 |
| J.R Beauty Training Ltd | Education | 2025 |
| J.R Nail Design Ltd | Other services | 2016 |
| J.R.P. (Colchester) Ltd | Construction | 2017 |
| J.S. Blyth & Sons Limited | Administrative & support | 2003 |
| J.U.C Limited | Health & social care | 2019 |
| J.W.S Fitting & Installation Ltd | Administrative & support | 2012 |
| J1 Brickwork Limited | Construction | 2017 |
| J1 Construction Limited | Construction | 2006 |
| J1H Racing Limited | Arts & recreation | 2024 |
| J56 Pigeon JV Limited | Other services | 2023 |
| J9 Consulting Ltd | Professional & scientific | 2019 |
| JA & BG Land Limited | Construction | 2003 |
| Jaat Property Limited | Real estate | 2024 |
| JAB Commercial Services Ltd | Professional & scientific | 2018 |
| Jabbari Capital Ltd | Real estate | 2024 |
| Jabond MAN Consulting Limited | Wholesale & retail | 2025 |
| Jacaw Estates Limited | Construction | 2011 |
| Jacens Utility Consulting Ltd | Construction | 2023 |
| Jack & Lubi Properties Limited | Real estate | 2024 |
| Jack Arnold (UK) Ltd | Construction | 2011 |
| Jack Arnold Group Ltd | Professional & scientific | 2020 |
| Jack Gladyng ODP Limited | Health & social care | 2016 |
| Jack Griffin Sales Solutions Ltd | Wholesale & retail | 2022 |
| Jack Linden Gray Ltd | Professional & scientific | 2025 |
| Jack of ALL Traders Ltd | Administrative & support | 2021 |
| Jack Sealey Limited | Wholesale & retail | 1977 |
| Jack's Food Shack Ltd. | Hospitality | 2018 |
| Jackandsonstransport Limited | Transport & logistics | 2025 |
| Jackie Spurr Consulting Ltd | Professional & scientific | 2011 |
| Jackjane Limited | Health & social care | 2019 |
| Jackrabbit Brewing Co. Ltd | Manufacturing | 2019 |
| Jackson Administration Ltd | Public administration | 2018 |
| Jackson Electrical Ltd | Construction | 2022 |
| Jackson Mortgage Brokers Limited | Financial services | 2024 |
| Jackson Warner Technical Ltd | Administrative & support | 2021 |
| Jacore Ltd | Real estate | 2022 |
| Jacqueline Court (Colchester) RTM Company Limited | Real estate | 2010 |
| Jacqueline Court (Freehold) Company Limited | Households | 2024 |
| Jacqui Robinson Education Centre Ltd | Education | 2013 |
| Jacqui Robinson Properties Ltd | Financial services | 2018 |
| Jadee's Nursing Agency Limited | Health & social care | 2019 |
| Jagne Holdings Limited | Financial services | 2024 |
| Jaguar Engineering Consultancy Ltd | Professional & scientific | 2021 |
| JAH Social Work Ltd | Health & social care | 2023 |
| JAI Llama Limited | Information & communication | 2019 |
| JAK Finch Hair Ltd | Other services | 2020 |
| Jakabim Consulting Ltd | Professional & scientific | 2018 |
| Jakoob&Co Ltd | Construction | 2020 |
| Jalfie Limited | Professional & scientific | 2012 |
| JAM Xperience Ltd | Wholesale & retail | 2025 |
| James & Lindsay Ltd | Financial services | 2003 |
| James Appleton Photography Limited | Arts & recreation | 2010 |
| James Arthur Limited | Financial services | 2023 |
| James C Santoro Sales Limited | Wholesale & retail | 2025 |
| James Carroll Limited | Financial services | 2008 |
| James Dean Developers Limited | Construction | 2025 |
| James Ferdi 2 Limited | Real estate | 2017 |
| James Ferdi Consulting Ltd | Professional & scientific | 2017 |
| James Ferdi Investments Limited | Real estate | 2017 |
| James Ferdi Ltd | Real estate | 2016 |
| James FOX Developments - Waterstock Limited | Real estate | 2018 |
| James Harrison Surveying Ltd | Professional & scientific | 2010 |
| James Johnson Productions Ltd | Professional & scientific | 2022 |
| James Lawrence Sailmakers Ltd. | Manufacturing | 1993 |
| James Lawson Planning Limited | Administrative & support | 2020 |
| James LEE Interiors Limited | Construction | 2016 |
| James Leigh Consulting Limited | Professional & scientific | 2008 |
| James Leigh Property Management Limited | Real estate | 2018 |
| James Martin Beds Ltd | Wholesale & retail | 2025 |
| James Martin Soft Furnishings Group Ltd | Extraterritorial | 2021 |
| James Varley Limited | Wholesale & retail | 2016 |
| James W Composites Ltd | Manufacturing | 2024 |
| Jamgar Limited | Information & communication | 2017 |
| Jamie C Services Ltd | Water & waste | 2017 |
| Jamie Loughead Limited | Professional & scientific | 2022 |
| Jamm Renewables Ltd | Construction | 2022 |
| Jammy Shows & Productions Limited | Arts & recreation | 2012 |
| Jamoh Ltd | Wholesale & retail | 2022 |
| Janchai EP Limited | Real estate | 2017 |
| Jane Little Business Consultancy Limited | Professional & scientific | 2025 |
| Jane Swann Psychology Ltd | Professional & scientific | 2020 |