| IT ALL Starts With a Breath Limited | Arts & recreation | 2023 |
| It's a Wrap Branding Ltd | Professional & scientific | 2017 |
| Itasushi Limited | Extraterritorial | 2014 |
| Itempire Holdings Ltd | Financial services | 2023 |
| Itempire Limited | Information & communication | 2020 |
| Itrak Wireless Limited | Administrative & support | 2010 |
| Ivorys Farm Limited | Real estate | 2025 |
| IVY Arch Studios Ltd | Information & communication | 2016 |
| Ivydore Investments Limited | Real estate | 2014 |
| Iworks Limited | Administrative & support | 2016 |
| J & D Dental Laboratory Ltd | Manufacturing | 2023 |
| J & D Whyte Ltd | Financial services | 2017 |
| J & H Massie Limited | Wholesale & retail | 2008 |
| J & JK Construction Limited | Construction | 2019 |
| J & M Green Ltd | Wholesale & retail | 2021 |
| J & R Flooring Solutions Ltd | Construction | 2022 |
| J and J Auto Repair Ltd | Wholesale & retail | 2023 |
| J Belton Plumbing and Bathrooms Ltd | Construction | 2006 |
| J C Diving Services Limited | Professional & scientific | 2017 |
| J C Management & Advisory Ltd | Professional & scientific | 2024 |
| J C Mcquillan Consultant Ltd | Professional & scientific | 2026 |
| J D Civils Group Ltd | Construction | 2024 |
| J DE B Films Ltd | Information & communication | 2008 |
| J E Green Contractors Ltd | Construction | 2019 |
| J G Prestige Cars Ltd | Wholesale & retail | 2020 |
| J James Roofing Ltd | Construction | 2022 |
| J K Rolling Ltd | Administrative & support | 2017 |
| J P Gale Limited | Information & communication | 2018 |
| J Valdinger Consulting Limited | Professional & scientific | 2025 |
| J W S Building Services Limited | Manufacturing | 1994 |
| J&D Groundworks Limited | Construction | 2008 |
| J&H GAS Heating Plumbing Bathrooms Limited | Construction | 2025 |
| J&H Properties and Lettings Ltd | Households | 2022 |
| J&T Specialists Limited | Professional & scientific | 2022 |
| J. E. B. Thatcher Limited | Real estate | 1991 |
| J.A.D. Estates Worldwide Limited | Real estate | 2022 |
| J.A.Longhurst Limited | Agriculture & fishing | 1958 |
| J.D. Properties and Letting Ltd | Construction | 2025 |
| J.G.H. Carpentry & Joinery Limited | Construction | 2013 |
| J.K. Leech (Fuels) Limited | Professional & scientific | 1984 |
| J.M. Flooring (Sussex) Ltd | Construction | 2026 |
| J2 Sussex Ltd. | Real estate | 2018 |
| J27 Digital Limited | Information & communication | 2013 |
| J8 Aero Consulting Ltd | Professional & scientific | 2022 |
| JAB Structures Limited | Professional & scientific | 2012 |
| Jacey Stores Limited | Wholesale & retail | 2010 |
| Jack Allen Ltd | Information & communication | 2018 |
| Jack Callaghan Media Limited | Information & communication | 2022 |
| Jack Caulfield Limited | Information & communication | 2026 |
| Jack in the Box Playgroup Limited | Education | 2010 |
| Jack Joseph Limited | Information & communication | 2022 |
| Jack Rafter Ltd | Manufacturing | 2017 |
| Jack Russell Technologies Ltd | Information & communication | 2021 |
| Jack Sears Care Ltd | Health & social care | 2022 |
| Jack Wood Home Improvements Ltd | Manufacturing | 2024 |
| Jacknbox Limited | Other services | 2005 |
| Jackson Griffiths Limited | Real estate | 2026 |
| Jackson Sales Consulting Ltd | Professional & scientific | 2026 |
| Jacob Mitchell Payne Ltd | Professional & scientific | 2026 |
| Jacob Renju Ltd | Other services | 2021 |
| Jade Business Consulting Ltd | Professional & scientific | 2024 |
| Jagmak Limited | Hospitality | 2025 |
| Jago Consultants Ltd | Administrative & support | 2013 |
| Jago Recruitment Ltd | Administrative & support | 2020 |
| Jagster Limited | Information & communication | 2021 |
| JAK Blake Investments Ltd | Real estate | 2021 |
| JAK Food Services Limited | Manufacturing | 2011 |
| Jalan-Jalan Productions LLP | | 2024 |
| JAM Home Improvements and Maintenance Ltd | Households | 2014 |
| JAM Project Management Limited | Administrative & support | 2008 |
| Jambo Records Limited | Information & communication | 2005 |
| Jamboree Events Company Ltd | Hospitality | 2023 |
| James Barnett Ltd | Manufacturing | 2018 |
| James Brothers Ltd | Manufacturing | 2015 |
| James Brown Digital Consulting Ltd | Professional & scientific | 2025 |
| James Burial Limited | Manufacturing | 2025 |
| James Dewsnap Audio Ltd | Arts & recreation | 2022 |
| James Ennis Photography Ltd | Professional & scientific | 2021 |
| James Kingston Limited | Professional & scientific | 2013 |
| James Leavers Limited | Professional & scientific | 2020 |
| James Oakley Media Limited | Professional & scientific | 2018 |
| James Paul (Car Sales) Limited | Wholesale & retail | 1998 |
| James Shea Consulting C.I.C. | Arts & recreation | 2016 |
| James Togneri Stoneworks Ltd | Construction | 2022 |
| Jamie Pierre Hughes Producing Ltd | Information & communication | 2025 |
| Jamieson Mills Limited | Real estate | 2014 |
| Jamin Productions Limited | Information & communication | 2007 |
| Jandb Prop Co Ltd | Real estate | 2020 |
| Jane Bennetts Second Spring Ltd | Information & communication | 2025 |
| Jane C. Oliver Educational Consultancy Limited | Education | 2008 |
| Jane Harrington Ltd | Information & communication | 2026 |
| Jane Law Limited | Wholesale & retail | 2000 |
| Jane Roberts Limited | Professional & scientific | 2003 |
| Janman Electrical Ltd | Construction | 2007 |
| January Projects Ltd | Arts & recreation | 2021 |
| Janus Systems & Design Limited | Administrative & support | 1998 |
| JAO Investments Ltd | Financial services | 2023 |
| Japan Experience Ltd | Administrative & support | 2013 |
| Japan Toys Limited | Wholesale & retail | 2022 |
| JAR Butler Ltd | Construction | 2019 |