| Humlet Medical Communications Ltd | Professional & scientific | 2022 |
| Hung TAI (Burgess Hill) Limited | Hospitality | 2020 |
| Hunter Homes Lettings Limited | Households | 2025 |
| Hunters Commercial Ltd | Real estate | 2025 |
| Hunters Estate Agents (Haywards Heath) LLP | | 2012 |
| Hurstwood Close (Haywards Heath) Management Company Limited | Households | 2017 |
| Hydras IT Limited | Information & communication | 2010 |
| Hydro Pneumatic Services Limited | Wholesale & retail | 1983 |
| I 2 I Online Limited | Professional & scientific | 2000 |
| I Clarke and SON Limited | Construction | 2015 |
| I Dream of Mangoes Ltd | Arts & recreation | 2026 |
| I-Tech Lewes Ltd | Other services | 2025 |
| Iceni Fire Limited | Professional & scientific | 2025 |
| ID Software Support Ltd | Information & communication | 2022 |
| Identity Property Investment Limited | Real estate | 2016 |
| Iesf Consulting Ltd | Professional & scientific | 2026 |
| Imagine Blinds & Shutters Ltd | Wholesale & retail | 2016 |
| Imperial Diagnostix Ltd | Wholesale & retail | 2022 |
| Incito Solutions Limited | Administrative & support | 2015 |
| Incrementum Mindset Ltd | Professional & scientific | 2019 |
| Indecs Contracts Ltd | Construction | 2012 |
| Independent Financial Limited | Financial services | 2020 |
| Independent Motor Factors Limited | Wholesale & retail | 2018 |
| Ineox LAB Ltd | Professional & scientific | 2023 |
| Ingham Groundwork Ltd | Construction | 2021 |
| Inheritance Data Limited | Information & communication | 2024 |
| Inholmes Orchard Residents Company Limited | Households | 1982 |
| Innovate Consult Ltd | Information & communication | 1995 |
| Inovee Limited | Information & communication | 2024 |
| Insight Accounting Services Ltd | Professional & scientific | 2019 |
| Insight Services (Sussex) Limited | Professional & scientific | 2014 |
| Insitu Consulting Ltd | Administrative & support | 2017 |
| Integrated Development Ltd | Professional & scientific | 2003 |
| Intelligent Inclusion Ltd | Professional & scientific | 2024 |
| Intent Support Ltd | Construction | 2012 |
| Interfaith Action | Information & communication | 2005 |
| International Bible Training College | Other services | 2017 |
| International Technology Consultants Limited | Administrative & support | 1990 |
| IPM - Interim Project Manager Ltd | Information & communication | 2025 |
| Isaac Place Management Company (Haywards Heath) Limited | Households | 2004 |
| Ishop Worldwide Limited | Wholesale & retail | 2015 |
| Isla Espiral Limited | Hospitality | 2013 |
| IST Carpentry Ltd | Manufacturing | 2023 |
| J C Capital Investments Limited | Financial services | 2023 |
| J EKE Limited | Professional & scientific | 2016 |
| J Ferguson Camera Services Limited | Professional & scientific | 2012 |
| J Glover Renovations Ltd | Construction | 2026 |
| J King Properties Limited | Real estate | 2017 |
| J S K Computing Limited | | 1989 |
| J Stratton Properties Ltd | Real estate | 2026 |
| J&J Accountants Ltd | Professional & scientific | 2005 |
| J. Enright Groundworks Limited | Construction | 2016 |
| J.D. Field & Sons Limited | Extraterritorial | 2013 |
| J.L.Collett Plumbing and Heating Limited | Construction | 2017 |
| J.R. Estates Limited | Real estate | 1986 |
| J23ARL Ltd | Construction | 2024 |
| Jacques Property Management Ltd | Real estate | 2026 |
| Jact Property Ltd | Construction | 2026 |
| JAD Financial Services Ltd | Financial services | 2024 |
| Jaiface Ltd | Arts & recreation | 2013 |
| JAKO10 Limited | Health & social care | 2021 |
| JAL 28 Limited | Professional & scientific | 2025 |
| James Hudson Interiors Limited | Construction | 2015 |
| James Macqueen Safety Consultancy Ltd | Administrative & support | 2014 |
| James Makin Wealth Management Limited | Professional & scientific | 2018 |
| Jamie P Benson Ltd Ltd. | Real estate | 2009 |
| Jamie Stratton Limited | Information & communication | 2026 |
| Jamjama Marketing Ltd | Professional & scientific | 2023 |
| Jarvis Education Ltd | Education | 2023 |
| Jasmine Jewel Ltd Ltd | Manufacturing | 2025 |
| JB Haulage&Clearance Ltd | Water & waste | 2024 |
| JBH Refurbishments Limited | Construction | 2008 |
| Jchatterjee Ltd | Health & social care | 2022 |
| JD Surveying Ltd | Construction | 2020 |
| Jefferies Funerals Limited | Other services | 2012 |
| Jersey Collections Limited | Wholesale & retail | 2024 |
| Jessica SC Moran Production Services Ltd | Information & communication | 2015 |
| Jessica Willis Treatment Room Ltd | Other services | 2026 |
| Jetminder Limited | Other services | 2023 |
| JG Brickwork Services Limited | Construction | 2015 |
| JGM Gardens Limited | Administrative & support | 2022 |
| JH & Co Brickwork Services Ltd | Construction | 2021 |
| Jigsaw Workplace Training Limited | Extraterritorial | 2024 |
| Jiminy Consulting Ltd | Professional & scientific | 2015 |
| Jimtin Ltd | Real estate | 2025 |
| JJK 15 Ltd | Real estate | 2025 |
| Jkrsp Ltd | Information & communication | 2016 |
| Jkswaves Ltd | Health & social care | 2022 |
| JLB Homes Limited | Real estate | 2021 |
| JLJ Care Company Ltd | Health & social care | 2024 |
| JM Moments Limited | Professional & scientific | 2025 |
| JM Transport & Logistics Ltd | Transport & logistics | 2024 |
| JMAC2 Limited | Professional & scientific | 2022 |
| JMC Solutions Surrey Ltd | Construction | 2022 |
| JMH Window Consultants Limited | Other services | 2022 |
| JMO Venture Capital Limited | Professional & scientific | 2022 |
| John Farrall (Building Contractor) Limited | Construction | 2001 |
| John Isaac Domestic Appliances Limited | Other services | 2010 |
| John Sterling Films Limited | Information & communication | 2002 |
| John Willis (Chemists) Limited | Real estate | 1968 |