| Intermedia FL Limited | Financial services | 2016 |
| Inventertainment Limited | Hospitality | 2017 |
| Inver Associates Ltd | Wholesale & retail | 2011 |
| Invicta Consultancy Limited | Professional & scientific | 2015 |
| Invocrown Limited | Information & communication | 1990 |
| Ironside (Sussex) Ltd | Construction | 2022 |
| Ironwood Carpentry Construction Ltd | Manufacturing | 2025 |
| IRRIG8ION Depot LLP | | 2011 |
| Isabella's Place Management Ltd | Households | 2022 |
| Isellphones Limited | Wholesale & retail | 2023 |
| Isla Cottages Freehold Management Company Limited | Real estate | 2012 |
| Island to Island Management Limited | Arts & recreation | 2009 |
| Istead-White Limited | Other services | 2019 |
| IT Junkys Ltd | Wholesale & retail | 2024 |
| Italian Sourdough Pizzeria Ltd | Manufacturing | 2025 |
| Itchenor Little Prep Academy Ltd | Education | 2026 |
| Itile Ltd | Construction | 2022 |
| Ivan Tihomir Properties Ltd | Real estate | 2020 |
| Izal Cleaning Ltd | Construction | 2019 |
| J & S Utility Projects Limited | Construction | 2023 |
| J a S Interiors Limited | Construction | 2015 |
| J Building Services & Installations Limited | Construction | 2020 |
| J Collins Electrical Ltd | Construction | 2025 |
| J Dickinson Holdings Ltd | Financial services | 2026 |
| J Electrical Services & Installations Limited | Construction | 2011 |
| J Fire Safety Services & Installations Limited | Construction | 2019 |
| J Gocher Communications Limited | Professional & scientific | 1999 |
| J K Berkhamsted Trading Limited | Real estate | 2014 |
| J O'Brien Security Limited | Administrative & support | 2012 |
| J Porter Accesses Limited | Construction | 2022 |
| J T Landscapes Ltd | Administrative & support | 2021 |
| J T Property Management (West Sussex) Ltd | Administrative & support | 2024 |
| J&B Builders & Roofing Specialists Limited | Construction | 2015 |
| J.J. & M. Ball Property Limited | Real estate | 2017 |
| J.R. Oxley Plumbing and Heating Limited | Construction | 2015 |
| J.S. Humidifiers Limited | Extraterritorial | 2011 |
| JA Consulting Holdings Limited | Professional & scientific | 2020 |
| Jacktradin Ltd | Wholesale & retail | 2026 |
| Jacobs Steel Commercial Ltd | Real estate | 2022 |
| Jacobs Steel Lettings Limited | Real estate | 2018 |
| Jaggs Motors Ltd | Wholesale & retail | 2023 |
| JAM Consultants Global Limited | Wholesale & retail | 2012 |
| James Buckman Limited | Professional & scientific | 2025 |
| James Lewis Medical Limited | Health & social care | 2012 |
| James Young Carpentry Limited | Administrative & support | 2016 |
| Jardean Ltd | Transport & logistics | 2024 |
| Jarka Aesthetika Limited | Professional & scientific | 2021 |
| Jasset Holdings Limited | Real estate | 2022 |
| Jayboy Ltd | Wholesale & retail | 2025 |
| JB Installations (Sussex) Limited | Construction | 2024 |
| JBA Sapres Ltd | Other services | 2011 |
| Jbcj Cleaning Ltd | Administrative & support | 2023 |
| Jbitalia Limited | Professional & scientific | 2015 |
| JC Roadways Ltd | Construction | 2026 |
| JCB Composites Ltd | Professional & scientific | 2025 |
| JCG Heating Solutions Ltd | Construction | 2023 |
| JCL Business Solutions Ltd | Information & communication | 2007 |
| Jcmedix Limited | Health & social care | 2016 |
| JCR Products Limited | Wholesale & retail | 2016 |
| JDM Asset Management Ltd | Households | 2021 |
| Jedi One Ltd | Water & waste | 2025 |
| Jermyn Construction Ltd | Construction | 2020 |
| Jesus Studio Ltd | Wholesale & retail | 2013 |
| JET Dreamers Ltd | Transport & logistics | 2026 |
| Jetair Limited | Transport & logistics | 2025 |
| JFM Homes Limited | Real estate | 2018 |
| JG Resourcing Ltd | Administrative & support | 2024 |
| JH & Chopsticks Limited | Hospitality | 2025 |
| JHY Holdings Ltd | Financial services | 2024 |
| JKW PR & Marketing Ltd | Professional & scientific | 2022 |
| Jnml Limited | Real estate | 2022 |
| JOB Done (Sussex) Limited | Construction | 2014 |
| Jodi and Sons CIC | Wholesale & retail | 2024 |
| Johnstone Moblie Tyre Fitter Ltd | Professional & scientific | 2026 |
| Joint Replacement Specialists Limited | Health & social care | 2020 |
| Jolly Roger Films Ltd | Information & communication | 2017 |
| Jones & Tomlin (Workshops) Limited | Wholesale & retail | 1956 |
| Joni Jacobs Pilates Ltd | Other services | 2022 |
| Joseph Heating Ltd | Construction | 2021 |
| Jpmg Print & Mail Services Limited | Manufacturing | 1999 |
| Juicenjoy Ltd | Hospitality | 2019 |
| June Rosina Community Interest Company | Health & social care | 2019 |
| Juniper Place (Eastwood Road) Management Limited | Households | 2019 |
| Just B Ltd | Information & communication | 2022 |
| Just Burgers Ltd | Hospitality | 2015 |
| Just Help One | Real estate | 2026 |
| Just Mortgages Southern Ltd | Financial services | 2024 |
| Justin H. Hill Limited | Professional & scientific | 2008 |
| JW and Sons Trading Ltd | Information & communication | 2021 |
| K B Computer Repairs Limited | Other services | 2020 |
| K Oldfield Limited | Other services | 2015 |
| K Oldfield Properties Ltd | Real estate | 2025 |
| K.Lacey(Engineers & Designers)Limited | Manufacturing | 1971 |
| Kafm Enterprises Ltd | Wholesale & retail | 2018 |
| KAI & Sunny Ltd | Arts & recreation | 2015 |
| Kanga Yoga Events Limited | Health & social care | 2016 |
| Kate Godwin Healing Limited | Other services | 2013 |
| Kayuka Designs Ltd | Information & communication | 2019 |
| KBO Limited | Transport & logistics | 2024 |
| KC Construction (Sussex) Ltd | Manufacturing | 2020 |