| Ilovegrowth Ltd | Transport & logistics | 2018 |
| Ilyas Projects Ltd | Construction | 2014 |
| Imperial Wedding Cars Ltd | Transport & logistics | 2023 |
| Improved Vision Limited | Extraterritorial | 1991 |
| Impulsus Limited | Information & communication | 2017 |
| Inclusive Tech Ltd | Information & communication | 2025 |
| India Gate Merston Limited | Hospitality | 2013 |
| Indian and Mediterranean Food Limited | Hospitality | 2024 |
| Indian Authentic Food Ltd | Hospitality | 2023 |
| Indianturkishsouthsea Ltd | Hospitality | 2025 |
| Indiego Build Ltd | Construction | 2020 |
| Infinite Beauty Ltd | Other services | 2018 |
| Infinity Food Supplies Ltd | Wholesale & retail | 2025 |
| Infuse 360 Ltd | Other services | 2016 |
| INK Doctors (Portsmouth) Limited | Arts & recreation | 2012 |
| Inquire Ltd | Administrative & support | 2017 |
| Inside OUT Developments (South) Ltd | Construction | 2015 |
| Insight and Motivation Ltd | Other services | 2011 |
| Inspector Homes Surveyors Ltd | Professional & scientific | 2022 |
| Integra Infosis Limited | Information & communication | 2024 |
| Intellectual Capital Group Ltd | Professional & scientific | 2019 |
| Interfrastic Software Limited | Information & communication | 2021 |
| Interior Design Academy Limited | Professional & scientific | 2016 |
| Interior Finishing Solutions Ltd | Construction | 2015 |
| Interiors Design Lorance Ltd | Construction | 2025 |
| Investase Limited | Professional & scientific | 2019 |
| IRC Consultancy Ltd | Professional & scientific | 2016 |
| Isabelle Busby Ltd | Professional & scientific | 2026 |
| Island Feather Limited | Manufacturing | 2016 |
| Isle of Wight Sales and Lettings Ltd | Real estate | 2025 |
| Isoni Luxe Limited | Wholesale & retail | 2025 |
| Isotech Sprayfoam Limited | Construction | 2003 |
| Issara Limited | Transport & logistics | 2024 |
| Iuliflor Ltd | Construction | 2017 |
| Ivanov Service UK Ltd | Construction | 2018 |
| Iyora Ltd | Information & communication | 2026 |
| J & L Fairhall Ltd | Real estate | 2016 |
| J & R Espiritu Limited | Health & social care | 2022 |
| J Cobbold Brickwork Ltd | Construction | 2018 |
| J H Lavery Ltd | Agriculture & fishing | 2025 |
| J P Akers Limited | Arts & recreation | 2013 |
| J P Mellish Ltd | Mining & quarrying | 2020 |
| J S Land Developers Limited | Real estate | 2017 |
| J Saunders Engineering Consultancy Limited | Professional & scientific | 2022 |
| J&A Newman Property Company Limited | Real estate | 2025 |
| J&A Residential Ltd | Real estate | 2026 |
| J.S. Consultancy Services Ltd | Professional & scientific | 1998 |
| J.V Deeping Limited | Administrative & support | 2020 |
| Jaags Property and Land Limited | Real estate | 2021 |
| Jaco Developments Limited | Real estate | 2024 |
| Jacob Carr Homes (Willow Park Management) Limited | Real estate | 2018 |
| Jade Oak (UK) Ltd | Wholesale & retail | 2013 |
| JAK Distribution Ltd | Wholesale & retail | 2025 |
| Jalika UK Ltd | Wholesale & retail | 2025 |
| Jamali Data Hive Ltd | Information & communication | 2024 |
| James Fencing Ltd | Construction | 2019 |
| James Potter Associates Ltd | Professional & scientific | 2015 |
| James Potter Developments Ltd | Construction | 2022 |
| James Sheehy Limited | Information & communication | 2016 |
| Jamesco Build Management Services Limited | Construction | 2019 |
| Japakoma Limited | Hospitality | 2019 |
| Jaquatica Limited | Agriculture & fishing | 2025 |
| Jarvie Property Developments Ltd | Real estate | 2023 |
| Jasmine Garden Services Ltd | Administrative & support | 2026 |
| Javora Limited | Real estate | 2021 |
| Jayasinghe Properties Ltd | Wholesale & retail | 2022 |
| Jaykaysquare Consultancy Ltd | Professional & scientific | 2026 |
| JAZ Terrace Limited | Real estate | 2017 |
| Jazup Ltd | Households | 2026 |
| JB Audio and Visual Limited | Construction | 2023 |
| JBC Residents Association Ltd | Households | 2025 |
| JBT Ltd | Construction | 2017 |
| JC8 Consulting Ltd | Information & communication | 2013 |
| JCC Construction Sites Limited | Construction | 2024 |
| JCG Associates Limited | Professional & scientific | 2013 |
| JCN Roofing Ltd | Construction | 2021 |
| Jdevans Group Limited | Construction | 2025 |
| JDF Assets Ltd | Real estate | 2019 |
| JDF Events Ltd | Arts & recreation | 2025 |
| Jeeves Cleaning Service Ltd | Administrative & support | 2025 |
| Jempark Properties Limited | Real estate | 2023 |
| Jenni & RUI Ltd | Real estate | 2025 |
| Jenny House Hair Ltd | Other services | 2022 |
| Jenny M London Limited | Wholesale & retail | 2013 |
| Jetsam Tech Ltd | Information & communication | 2020 |
| Jewellesque Enterprise Ltd | Hospitality | 2024 |
| JH2 Consultancy Ltd | Professional & scientific | 2022 |
| Jj's Jawns Ltd | Wholesale & retail | 2025 |
| JK Accounts Portsmouth Ltd | Professional & scientific | 2023 |
| JK Geological Services Limited | Mining & quarrying | 2012 |
| JKR Ventures Limited | Professional & scientific | 2024 |
| JLD Rental Solutions Ltd | Real estate | 2022 |
| JM Welding Services Ltd | Professional & scientific | 2018 |
| JMT GEO Services Limited | Professional & scientific | 2016 |
| Joam Construction Services Ltd | Construction | 2014 |
| John A.Thompson Memorial Trust | Health & social care | 1964 |
| John Barber Electrical Limited | Construction | 2007 |
| John Mcghee Brickwork Ltd | Construction | 2019 |
| John Northover Limited | Water & waste | 2024 |
| Johnathanbuild Ltd | Construction | 2025 |