| Ivor-View Windows & Doors Limited | Construction | 2017 |
| Iwobotics Ltd | Professional & scientific | 2025 |
| Iyla Property Services Ltd | Real estate | 2021 |
| Izaaya Group Ltd | Wholesale & retail | 2025 |
| Izzie Solutions Limited | Other services | 2025 |
| J & G Home Improvements Ltd | Households | 2014 |
| J & T Drainage Solutions Limited | Water & waste | 2013 |
| J a Exotic Cars Ltd | Wholesale & retail | 2022 |
| J a Residential Limited | Real estate | 2022 |
| J and C Stephens Ltd | Administrative & support | 2008 |
| J F L Legal Recruitment.Co.Uk Ltd | Other services | 2010 |
| J Hayes Plumbing and Heating Ltd | Construction | 2025 |
| J J Walkies Limited | Professional & scientific | 2020 |
| J K Chimney Sweeps Limited | Construction | 2026 |
| J K Hazel Limited | Manufacturing | 2017 |
| J K Munch Box Ltd | Wholesale & retail | 2018 |
| J Kelly Consulting Ltd | Public administration | 2021 |
| J L Telemarketing Ltd | Administrative & support | 2010 |
| J N Carpentry & Construction Ltd | Construction | 2016 |
| J P S Immigration Limited | Administrative & support | 2008 |
| J Richardson Consulting Ltd | Professional & scientific | 2025 |
| J W Electrical Services (Crawley) Ltd | Construction | 2009 |
| J&A Events Ltd | Information & communication | 2022 |
| J&H Global Logistics Ltd | Transport & logistics | 2025 |
| J&N Fire Solution Ltd | Public administration | 2025 |
| J. & M. Brown (Coaches) Limited | Transport & logistics | 1976 |
| J. Accountax Limited | Professional & scientific | 2018 |
| J. Louis Property Group Ltd | Real estate | 2025 |
| J.A.G Building Services Limited | Administrative & support | 2024 |
| J.C. Mackinlay and Co. Limited | Wholesale & retail | 1949 |
| J.E.M. (UK) Limited | Administrative & support | 2011 |
| J.E.N Beauty Lounge Ltd | Wholesale & retail | 2026 |
| J.E.N Property Rental Ltd | Real estate | 2023 |
| J94 Care Services Ltd | Health & social care | 2020 |
| J9UPP Ltd | Wholesale & retail | 2025 |
| JA Autos Crawley Ltd | Wholesale & retail | 2015 |
| JA Delivery Services Ltd | Other services | 2014 |
| JA Parcels Ltd | Transport & logistics | 2024 |
| JA5 Cars Ltd | Wholesale & retail | 2025 |
| JA5 Media Ltd | Professional & scientific | 2025 |
| JAC Capital Ltd | Financial services | 2025 |
| JAC Ecom Ltd | Education | 2023 |
| Jack Frost Tackle Ltd. | Wholesale & retail | 1996 |
| Jacks Amazon Club Ltd | Transport & logistics | 2020 |
| Jacobs, Young & Westbury Limited | Administrative & support | 1900 |
| Jacs and Co Services Limited | Other services | 2018 |
| Jade Solutions Ltd | Construction | 2024 |
| Jagger Property Investments Limited | Real estate | 2026 |
| Jagsll Ltd | Wholesale & retail | 2024 |
| Jaish Limited | Health & social care | 2025 |
| Jalandari Ltd | Wholesale & retail | 2021 |
| Jalex Limited | Wholesale & retail | 2023 |
| JAM Coder Ltd | Information & communication | 2022 |
| James Chandler (Lewes) Limited | Wholesale & retail | 1929 |
| James the Freelancer Ltd | Information & communication | 2007 |
| James Worby Agencies Ltd | Wholesale & retail | 2023 |
| James Wright Properties Limited | Real estate | 2021 |
| Jamjar Pet Ltd | Professional & scientific | 2024 |
| Jarvis Fighthub Ltd | Arts & recreation | 2025 |
| Jasco Links UK Limited | Health & social care | 2023 |
| Jasmin's Beauty Limited | Other services | 2020 |
| Jasso Ltd | Information & communication | 2026 |
| Jatinsuriconsultancyservice Limited | Professional & scientific | 2025 |
| Javan Projects Limited | Information & communication | 2018 |
| Jaxcraft Limited | Professional & scientific | 2009 |
| Jaymaz Consulting Ltd | Wholesale & retail | 2017 |
| Jazz Management Company Limited | Real estate | 1991 |
| JB Management Services Limited | Administrative & support | 2014 |
| JB21 Ltd | Administrative & support | 2025 |
| JBK Solutions Ltd | Health & social care | 2021 |
| JC Kitchen Installations Limited | Construction | 2015 |
| JC Wooden Works Ltd | Manufacturing | 2025 |
| Jcak Ltd | Professional & scientific | 2017 |
| JCC Collective Ltd | Real estate | 2026 |
| JCM Global Ltd | Wholesale & retail | 2019 |
| JCS Quality Solutions Ltd | Professional & scientific | 2017 |
| JD Properties & Developments Ltd | Real estate | 2025 |
| Jdee Property Ltd | Real estate | 2021 |
| Jdht Holdings Ltd | Professional & scientific | 2022 |
| JDV Properties Limited | Real estate | 2025 |
| JDV Property Services Ltd | Construction | 2024 |
| JE Leather Seat Covers Ltd | Manufacturing | 2019 |
| JE Smart Repairs Ltd | Wholesale & retail | 2024 |
| Jedi Repairs Ltd | Wholesale & retail | 2024 |
| Jelenas Music School Ltd | Education | 2021 |
| JEN Wilkes Learning Ltd | Professional & scientific | 2026 |
| Jenner Building Contractors Limited | Construction | 2002 |
| JEP Property Ltd | Construction | 2006 |
| Jeppesen Intermediate I Limited | Financial services | 2025 |
| Jeppesen Intermediate II Limited | Financial services | 2025 |
| Jeppesen U.K. Limited | Other services | 1977 |
| Jeppesen UK Holdings Limited | Financial services | 2025 |
| Jericho London Limited | Wholesale & retail | 2024 |
| Jersey (Crawley) Management Company Limited | Households | 1983 |
| Jessica J Billups Limited | Wholesale & retail | 2021 |
| Jetseeker Ltd | Administrative & support | 2025 |
| Jettsons Haulage Ltd | Transport & logistics | 2024 |
| JF Accountax Ltd | Professional & scientific | 2023 |
| JF Lapuk Limited | Hospitality | 2022 |
| JGM Homes Ltd | Real estate | 2025 |