| Isaac Timmins Limited | Professional & scientific | 1929 |
| Isabella Services Limited | Administrative & support | 2025 |
| Isco Ltd | Wholesale & retail | 2024 |
| ISD Civil Engineering Limited | Construction | 2015 |
| Iselectcarsales Ltd | Wholesale & retail | 2025 |
| Isem Properties Ltd | Real estate | 2025 |
| Ises Trading Ltd | Wholesale & retail | 2026 |
| ISH Retailer Ltd | Wholesale & retail | 2025 |
| Islands Chalets Limited | Administrative & support | 2024 |
| ISM Driving School Ltd | Education | 2024 |
| ISM Healthcare Limited | Health & social care | 2015 |
| Ismaeels Frozen Foods Ltd | Wholesale & retail | 2026 |
| Ismart Bay Hall Ltd | Professional & scientific | 2014 |
| ISPACE5 Community Interest Company | Information & communication | 2015 |
| Israybah Ltd | Wholesale & retail | 2023 |
| Isrpharm Ltd | Health & social care | 2022 |
| Issue Mend Ltd | Information & communication | 2024 |
| Istanbul Barbers HD Limited | Other services | 2019 |
| Istanbul Huddersfield Limited | Other services | 2023 |
| Isum Trading Ltd | Wholesale & retail | 2025 |
| Isupport Childrens Services Ltd | Health & social care | 2023 |
| Isupport Recruitment Ltd | Professional & scientific | 2023 |
| Isupport Services Ltd | Health & social care | 2020 |
| Isyd Ltd | Real estate | 2025 |
| Isysuk Ltd | Information & communication | 2018 |
| IT by Design Limited | Manufacturing | 2000 |
| IT Figures Financial Consultants Limited | Professional & scientific | 1998 |
| IT Global Communication Ltd | Wholesale & retail | 2025 |
| IT Resolved Ltd | Information & communication | 2025 |
| Italian Fastfood T/A Pizza Cucina Ltd | Hospitality | 2021 |
| Italtec and Trading Ltd | Manufacturing | 2021 |
| Itch Newco Limited | Professional & scientific | 2014 |
| Itch Propco Limited | Real estate | 2014 |
| Iteach Tuition Limited | Education | 2018 |
| ITS Brix Properties Ltd | Real estate | 2025 |
| Ittia Real Estate Limited | Real estate | 2023 |
| ITX Developments Limited | Information & communication | 2025 |
| IU Active Limited | Arts & recreation | 2025 |
| IU Group Limited | Wholesale & retail | 2025 |
| Iukh NLT Limited | Financial services | 2021 |
| Iventure Outdoor Group Ltd | Information & communication | 2021 |
| IVS Independent Volkswagen Specialist Limited | Wholesale & retail | 2021 |
| Ivtmi UK Ltd | Construction | 2025 |
| IVY Green Ltd | Hospitality | 2015 |
| Ivymay Animal and Livestock Services Ltd | Agriculture & fishing | 2025 |
| IZ and AZ Ltd | Wholesale & retail | 2024 |
| Izisam PVT Ltd | Other services | 2022 |
| Izloo Ltd | Real estate | 2021 |
| Izumi UK Limited | Financial services | 2016 |
| IZZ Trading Limited | Wholesale & retail | 2023 |
| J & a Farming and Contracting Work Ltd | Agriculture & fishing | 2022 |
| J & C Pritchard Property Investments Limited | Real estate | 2024 |
| J & E Rosenberg Limited | Financial services | 2017 |
| J & SW Holdings Ltd | Transport & logistics | 2025 |
| J & W Gibb & Sons Limited | Wholesale & retail | 1983 |
| J a M Sisters Property Limited | Real estate | 2021 |
| J a Properties (Huddersfield) Ltd | Extraterritorial | 2010 |
| J B Lingard Limited | Real estate | 2026 |
| J B Mortgages Ltd | Financial services | 2017 |
| J C Burkinshaw Agricultural Contractor Ltd | Agriculture & fishing | 2025 |
| J C Nixon Home Improvements Ltd | Construction | 2026 |
| J D Flack Limited | Wholesale & retail | 1961 |
| J D L Convenience Co Ltd | Wholesale & retail | 2014 |
| J Dyson Electrical Services Limited | Construction | 2017 |
| J Ellis Ltd | Transport & logistics | 2019 |
| J F R Property Management Limited | Real estate | 2023 |
| J G Chappell Limited | Professional & scientific | 2011 |
| J G L Holdings Limited | Professional & scientific | 2024 |
| J H Joinery & Construction Ltd | Construction | 2016 |
| J Hodge (Bookkeeping) Limited | Administrative & support | 2013 |
| J Holmes Property Ltd | Real estate | 2025 |
| J I C Engineering Ltd | Professional & scientific | 2026 |
| J J Embroidery Limited | Wholesale & retail | 2017 |
| J Joinery and Construction Ltd | Manufacturing | 2025 |
| J K Ceilings & Partitions (Hudd) Ltd | Real estate | 2016 |
| J K Medicare Limited | Health & social care | 2017 |
| J K Senior Building Contractor Limited | Construction | 2014 |
| J Khalid Ltd | Health & social care | 2024 |
| J M & V J Howard Limited | Agriculture & fishing | 2004 |
| J M Motorsport Ltd | Wholesale & retail | 2025 |
| J Movers Ltd | Transport & logistics | 2025 |
| J Murphy Properties Ltd | Real estate | 2016 |
| J P Mcdonagh Developments Ltd | Construction | 2023 |
| J P Online Ltd | Wholesale & retail | 2025 |
| J P R Plant Hire Ltd | Construction | 2020 |
| J P Transport Ltd | Transport & logistics | 2021 |
| J Paxman Landscapes Limited | Administrative & support | 2016 |
| J R H Fabrications Ltd | Construction | 2005 |
| J S Mensah Limited | Other services | 2024 |
| J S Waite Partnership LLP | | 2021 |
| J Speed Electrical Limited | Construction | 2025 |
| J T Grosvenor Limited | Manufacturing | 2019 |
| J T Properties (Yorks) Limited | Real estate | 2020 |
| J Taylor Signs Limited | Manufacturing | 2016 |
| J Transport Global Ltd | Transport & logistics | 2020 |
| J W Electrical (Huddersfield) Ltd | Construction | 2021 |
| J W Kaye (Holmfirth) Ltd | Wholesale & retail | 2025 |
| J W News HFD Ltd | Wholesale & retail | 2024 |
| J W Residential Limited | Real estate | 2016 |
| J&G Tree Contractors Ltd | Agriculture & fishing | 2026 |