| Island Landscapes Limited | Administrative & support | 1994 |
| Island Pigs Ltd | Agriculture & fishing | 2012 |
| Island Plastering Ltd | Construction | 2019 |
| Island Synergy Ltd | Financial services | 2023 |
| ISO Construct Limited | Construction | 2025 |
| ISO Property Investments Limited | Real estate | 2021 |
| Isolutions (UK) Limited | Information & communication | 2010 |
| IT 4 Offices Limited | Information & communication | 2009 |
| IT Fleet Automotive Limited | Wholesale & retail | 2001 |
| IT Key Ltd | Information & communication | 2025 |
| IT Slaps Ltd | Construction | 2025 |
| IT Traders UK Ltd | Wholesale & retail | 2003 |
| It's ALL Personal Ltd | Wholesale & retail | 2008 |
| Italian Cranes Engineering Ltd | Construction | 2026 |
| Italiano Bulk Ltd | Wholesale & retail | 2025 |
| ITC Consultancy Services Ltd | Professional & scientific | 2023 |
| Itcareervalley UK Limited | Information & communication | 2010 |
| Itech Services & Repairs Limited | Construction | 2015 |
| Iteng Translations Ltd | Professional & scientific | 2021 |
| ITG Instructor Training Ltd | Health & social care | 2009 |
| Iththitree Property Limited | Real estate | 2025 |
| Itigai Limited | Information & communication | 2025 |
| ITS Legacy Ltd | Wholesale & retail | 2025 |
| It’S a Barklife Ltd | Other services | 2024 |
| It’S ALL at Number Eleven Limited | Wholesale & retail | 2024 |
| Ivan Henderson Consultancy Limited | Professional & scientific | 2008 |
| Ivan Lazarov Ltd | Transport & logistics | 2023 |
| Ivanhoe Associates Limited | Households | 1986 |
| Ivckservices Ltd | Manufacturing | 2024 |
| Ivell Marketing & Logistics Limited | Administrative & support | 1998 |
| Ivor Rose Limited | Financial services | 2015 |
| Ivory Recruitment Services Ltd | Administrative & support | 2024 |
| Ivory Taylor Beauty Ltd | Other services | 2023 |
| Ivory Taylor Hair Dressing Ltd | Other services | 2023 |
| Ivory Tree Ltd | Real estate | 2021 |
| IVY Lodge Farm Limited | Agriculture & fishing | 1997 |
| IVY Lodge Road 1 Limited | Construction | 2024 |
| IVY Practitioner Limited | Health & social care | 2016 |
| Ivygate Property Management Ltd | Extraterritorial | 2020 |
| Ivygate Solutions Ltd | Education | 2025 |
| IWANT2NETWORK Ltd | Administrative & support | 2024 |
| IWS Developments Ltd | Manufacturing | 2015 |
| Iwsb Services Limited | Professional & scientific | 2023 |
| Iznimuneer Limited | Health & social care | 2017 |
| J & D Hinton Limited | Wholesale & retail | 2013 |
| J & H Housing Ltd | Real estate | 2021 |
| J & J Nails & Spa Ltd | Other services | 2023 |
| J & K Rattledge Holdings Limited | Financial services | 2024 |
| J & K'S Catering Limited | Hospitality | 2024 |
| J & L General Holdings Ltd | Professional & scientific | 2003 |
| J & M Holdings (Colchester) Limited | Real estate | 2005 |
| J & M Storage (Colchester) Limited | Transport & logistics | 2026 |
| J a Overton Limited | Real estate | 1944 |
| J and J Property Holdings Limited | Real estate | 2003 |
| J and M Resources Limited | Wholesale & retail | 2010 |
| J B Spares Limited | Wholesale & retail | 2008 |
| J Bowyer Property Improvements Limited | Construction | 2026 |
| J Burgess & Sons Limited | Wholesale & retail | 2005 |
| J C M Building Limited | Construction | 2016 |
| J C N Design Limited | Administrative & support | 2008 |
| J Clarke Builders Ltd | Construction | 2005 |
| J Cowens Associates Ltd | Professional & scientific | 2014 |
| J D C Consulting Ltd | Construction | 2020 |
| J D Hearn Ltd | Transport & logistics | 2018 |
| J D P Property Maintenance Ltd | Construction | 2026 |
| J D Roofing & Building Contractors Ltd | Construction | 2026 |
| J Doubleday Building Services Limited | Construction | 2009 |
| J Drainage Ltd | Water & waste | 2023 |
| J F Tree Specialist Limited | Agriculture & fishing | 2012 |
| J Foweraker Services Limited | Construction | 2014 |
| J G Wright Thermal Services Ltd | Construction | 2021 |
| J H E Ltd | Administrative & support | 2024 |
| J H Educational Services Limited | Education | 2013 |
| J J Health Consult Limited | Health & social care | 2023 |
| J Lawrence Rail Ltd | Construction | 2019 |
| J M Cutter Limited | Administrative & support | 2007 |
| J M Flooring (Essex) Limited | Construction | 2022 |
| J M Lambert Ltd | Professional & scientific | 2020 |
| J M Price Ltd | Health & social care | 2007 |
| J M S Vehicle Services Ltd | Wholesale & retail | 2000 |
| J M Wakeling Independent Financial Advisers Limited | Financial services | 2009 |
| J N V Print Limited | Administrative & support | 2000 |
| J North Limited | Construction | 2014 |
| J P F Fire Protection Ltd | Construction | 2009 |
| J P Financial Solutions Ltd | Financial services | 2016 |
| J Pollard Group Ltd | Wholesale & retail | 2026 |
| J Purser Heating Ltd | Construction | 2024 |
| J S Duke Consulting Ltd | Financial services | 2013 |
| J Sail Consultants Ltd | Financial services | 2022 |
| J T Hancock and Associates Limited | Professional & scientific | 2009 |
| J T R Rail Ltd | Construction | 2018 |
| J T Services Colchester Limited | Construction | 2013 |
| J Taylor Site Surveying Limited | Professional & scientific | 2011 |
| J Tipple Holdings Ltd | Construction | 2019 |
| J W Painting Limited | Construction | 2003 |
| J Waddell Transport Limited | Transport & logistics | 2002 |
| J Whitnell Plumbing and Heating Ltd | Construction | 2019 |
| J&D Global Ltd | Wholesale & retail | 2020 |
| J&J Carpet Fitting Services Limited | Wholesale & retail | 2013 |
| J&J Contract Cleaning Limited | Administrative & support | 2013 |