| Iqtile Limited | Construction | 2018 |
| IR Fitness and Health Solutions Limited | Arts & recreation | 2016 |
| IR Scaffolding Berkshire Ltd | Construction | 2024 |
| Irum Atlas Ltd | Wholesale & retail | 2021 |
| Irvine-Whitlock Limited | Professional & scientific | 1966 |
| Isabelle J D Keenan Limited | Professional & scientific | 2023 |
| Isapinmotion Ltd | Arts & recreation | 2024 |
| Isbill Services Limited | Extraterritorial | 2023 |
| Iscribo Limited | Professional & scientific | 2020 |
| Isemo Vision Limited | Wholesale & retail | 2023 |
| Isfraser Limited | Professional & scientific | 2006 |
| Ishopping Ltd | Wholesale & retail | 2025 |
| Islamic Wills Ltd | Other services | 2025 |
| Isle of Wight ZOO Limited | Arts & recreation | 2021 |
| Isra Bakes Ltd | Hospitality | 2022 |
| Istanbul Pizza House Ltd | Hospitality | 2015 |
| Istim UK Ltd | Transport & logistics | 2000 |
| ISW Assessment & Expertise Ltd | Professional & scientific | 2021 |
| ISW Assessment and Consultancy Limited | Administrative & support | 2017 |
| ISW Assessment and Contact Centre Ltd | Administrative & support | 2023 |
| Isylife Limited | Professional & scientific | 2014 |
| IT Expert Consultancy Services Limited | Administrative & support | 2012 |
| IT First Solutions Ltd | Information & communication | 2020 |
| IT World Strategy Ltd | Professional & scientific | 2021 |
| It-Cfo Limited | Wholesale & retail | 2008 |
| Italian Continental Stores Limited | Wholesale & retail | 1991 |
| Italian Food Network Ltd | Hospitality | 2019 |
| Itech Pro Services Ltd | Wholesale & retail | 2012 |
| Itinerys UK Limited | Professional & scientific | 2014 |
| Itlt Photography Ltd | Professional & scientific | 2022 |
| ITS Just Genetics Ltd | Education | 2026 |
| Itsm Transformations Limited | Professional & scientific | 2012 |
| Ivory Haze Ltd | Information & communication | 2011 |
| IVR247 Limited | Information & communication | 2025 |
| IW ( Franchising ) Consulting Ltd | Professional & scientific | 2023 |
| Iwiew Communication Ltd | Manufacturing | 2025 |
| Iyers Holdings Limited | Hospitality | 2024 |
| Izax Limited | Health & social care | 2015 |
| Izuga Ltd | Information & communication | 2014 |
| J & C Autos Bodywork Ltd | Wholesale & retail | 2018 |
| J & K Plant Hire Limited | Administrative & support | 2009 |
| J a D Transport & Forwarding Limited | Transport & logistics | 2020 |
| J a Heath Roofing and Construction Limited | Construction | 2020 |
| J D N (Holdings) Limited | Financial services | 2013 |
| J Draycott Consulting Ltd | Information & communication | 2025 |
| J H Craufurd Builders Limited | Construction | 2006 |
| J Harmes Demolition & Recycling Limited | Extraterritorial | 2007 |
| J Harmes Demolition Limited | Construction | 2006 |
| J Hutchins Investments Limited | Financial services | 2021 |
| J Jeczalik Limited | Information & communication | 2006 |
| J K London Investments Limited | Wholesale & retail | 2019 |
| J P Design Limited | Construction | 2005 |
| J P Design Projects Ltd | Construction | 2024 |
| J P Higgins Limited | Construction | 2006 |
| J Powell Property Holdings Ltd | Construction | 2025 |
| J R L Construction & Maintenance Limited | Construction | 2007 |
| J S Haulage Ltd | Transport & logistics | 2023 |
| J S Leisure Vehicles Limited | Wholesale & retail | 2015 |
| J S Property Maintenance Contractors Limited | Real estate | 2007 |
| J Scott & Co Solicitors Limited | Professional & scientific | 2014 |
| J Squared Services Ltd | Wholesale & retail | 2021 |
| J Wilson Interior Design Ltd | Construction | 2017 |
| J&Rg Trading Ltd | Wholesale & retail | 2026 |
| J&S Cornford Limited | Financial services | 2024 |
| J-Tec Composite Solutions Ltd | Professional & scientific | 2018 |
| J. & B. Emmett Limited | Administrative & support | 1937 |
| J. D. Woodwork Limited | Construction | 2013 |
| J.J. Waterman & Co Limited | Real estate | 1989 |
| J.O.G.A. Consulting Limited | Information & communication | 2005 |
| J.O.G.A. Property Investments Limited | Real estate | 2016 |
| J.P. Whelan & Sons (Construction) Limited | Construction | 1968 |
| J.P. Whelan (Investments) Limited | Professional & scientific | 1973 |
| J.P. Whelan Homes Limited | Construction | 1967 |
| J4T Properties Ltd | Real estate | 2023 |
| Jaanaco Trading & Consulting Ltd | Wholesale & retail | 2025 |
| Jaay Consulting Ltd | Professional & scientific | 2022 |
| Jack and Master Associates Limited | Construction | 2020 |
| Jack Door Windows Limited | Construction | 2007 |
| Jack Driving Ltd | Administrative & support | 2017 |
| Jack Laurie Limited | Professional & scientific | 2022 |
| Jackal Productions Limited | Information & communication | 2006 |
| Jackfruit Palace Ltd | Hospitality | 2025 |
| JACKO14 Ltd | Real estate | 2023 |
| Jackontrack Ltd | Health & social care | 2023 |
| Jackson Care Limited | Health & social care | 2014 |
| Jackson Development Services Limited | Professional & scientific | 2017 |
| Jackson Enterprise FIC Ltd | Real estate | 2021 |
| Jacquard Developments Limited | Information & communication | 2008 |
| Jacques Ltd | Administrative & support | 2020 |
| Jade Brick Investments Ltd | Real estate | 2021 |
| Jade Jones Ltd | Other services | 2026 |
| Jafm Properties Ltd | Real estate | 2024 |
| Jagho Cloud Services Ltd | Information & communication | 2018 |
| Jagprops Limited | Arts & recreation | 2002 |
| Jaimaa Consultant Ltd | Professional & scientific | 2016 |
| Jaipur Bloodstock Management Limited | Real estate | 2016 |
| JAM JAR Properties Limited | Real estate | 2017 |
| JAM Property Enterprises Ltd | Real estate | 2021 |
| James Adam & Company Limited | Professional & scientific | 2003 |
| James Electrical Installation Services Limited | Construction | 2023 |