| Inforsight Limited | Information & communication | 1997 |
| Infrastructure Design Studio Limited | Construction | 2006 |
| Ingleside Heritage Limited | Hospitality | 2008 |
| Ingrid Rossi London Ltd | Wholesale & retail | 2018 |
| Innovation Automotive Ltd | Wholesale & retail | 2017 |
| Inshore Systems Ltd | Professional & scientific | 2011 |
| Inside OUT of U Limited | Manufacturing | 2020 |
| Inspirati Services Ltd | Information & communication | 2025 |
| Inspire Defence and Security Ltd | Professional & scientific | 2014 |
| Inspire First Training Ltd | Other services | 2024 |
| Inspire Network Holdings Global Ltd | Other services | 2025 |
| Intac Network Ltd | Information & communication | 2021 |
| Intaconnet Limited | Information & communication | 2001 |
| Interfeed UK Limited | Wholesale & retail | 2010 |
| Interim GC Services Limited | Professional & scientific | 2023 |
| Interior Walls Limited | Extraterritorial | 1996 |
| International Corporate Affairs Services Limited | Professional & scientific | 1988 |
| Intervelo UK Limited | Administrative & support | 2001 |
| Invero AI Limited | Information & communication | 2025 |
| Invicta Performance Solutions Ltd | Professional & scientific | 2021 |
| IO Shield Limited | Information & communication | 2018 |
| Iosys Limited | Information & communication | 1988 |
| Ipsum Quest Limited | Information & communication | 2020 |
| Irongate Limited | Professional & scientific | 1999 |
| Isabella Power Ltd | Manufacturing | 2013 |
| Isas Online Limited | Administrative & support | 2014 |
| Iservice Solutions Limited | Information & communication | 2001 |
| Isgus UK Limited | Administrative & support | 2005 |
| IT and Cloud Solutions Limited | Professional & scientific | 2015 |
| Ithacal Ltd | Professional & scientific | 2026 |
| ITS My Money Limited | Professional & scientific | 2006 |
| IVY Nail Lounge Ltd | Other services | 2021 |
| IZC Ltd | Other services | 2025 |
| J a Properties (UK) Limited | Real estate | 2005 |
| J Barnes Property Ltd | Real estate | 2021 |
| J C Scott Ltd | Construction | 2022 |
| J Haddrell Consultants Ltd | Professional & scientific | 2020 |
| J J Power Limited | Energy | 2009 |
| J P Noble Limited | Professional & scientific | 2017 |
| J P Williams Limited | Professional & scientific | 2006 |
| J R Court Ltd | Professional & scientific | 2012 |
| J R Leach Limited | Wholesale & retail | 2016 |
| J R Smith Builders Ltd | Construction | 2016 |
| J West Developments Ltd | Construction | 2019 |
| J. J. Hall Ltd | Construction | 2006 |
| J.C. Swann Limited | Construction | 2003 |
| J.F.W Limousines Ltd | Administrative & support | 2021 |
| J.R. Holden & Sons Ltd. | Construction | 2006 |
| JAC Fit OUT Ltd | Construction | 2017 |
| Jaced SPV Limited | Construction | 2025 |
| Jackets (Caterers) Limited | Hospitality | 1979 |
| Jacks Brasserie Limited | Hospitality | 2018 |
| Jagarne Ltd | Construction | 2023 |
| JAH Furniture Ltd | Wholesale & retail | 2013 |
| Jake Construction Consulting Ltd | Professional & scientific | 2015 |
| Jalech Limited | Administrative & support | 2017 |
| JAM JAR Enterprises Ltd | Hospitality | 2022 |
| James Allison Kitchens and Bathrooms Ltd | Administrative & support | 2014 |
| James Slater (Surveyors) Limited | Professional & scientific | 2008 |
| Jaytee Creative Ltd | Administrative & support | 2014 |
| Jaytien Limited | Wholesale & retail | 2023 |
| Jazzfunky Ltd | Extraterritorial | 2022 |
| Jazzy Homes Limited | Construction | 2014 |
| Jazzy Maxwell Limited | Construction | 2018 |
| Jazzy Rentals Limited | Real estate | 2024 |
| JB Window Cleaning Services Limited | Administrative & support | 2025 |
| JBP Investments Limited | Administrative & support | 2017 |
| JC Brown Services Ltd | Construction | 2025 |
| Jcrisp Ltd | Information & communication | 2021 |
| JD Finance Limited | Financial services | 1999 |
| JDC Fire Ltd | Construction | 2021 |
| Jeff Stevens Ltd | Professional & scientific | 2017 |
| Jeffries Paget Construction Ltd | Construction | 2022 |
| JEN Winnett Art Ltd | Wholesale & retail | 2021 |
| Jeneng Ltd | Manufacturing | 2022 |
| Jeremy Harrold Consulting Ltd | Other services | 2016 |
| Jervis Caves & Canning Ltd | Hospitality | 2008 |
| JET Heritage Ltd | Other services | 2006 |
| JHR Interior Architecture and Design Ltd | Real estate | 2011 |
| Jigsaw Consulting Services Limited | Professional & scientific | 2018 |
| Jigsaw Housing Ltd | Real estate | 2008 |
| JLA Cirencester Ltd | Real estate | 2019 |
| JM Ward & Sons Ltd | Financial services | 2025 |
| JMR Consultants Ltd | Professional & scientific | 2019 |
| Jmrpm Ltd | Construction | 2023 |
| JN RPP Holdings Ltd | Other services | 2015 |
| JNT Limited | Manufacturing | 2024 |
| Jody Stevens Limited | Wholesale & retail | 2020 |
| JOE Miles Ltd | Manufacturing | 2026 |
| Joelle Consulting Ltd | Professional & scientific | 2013 |
| John Alison Land & Research Ltd | Real estate | 2011 |
| Joli Beau Limited | Wholesale & retail | 2012 |
| Jolie Maison Limited | Manufacturing | 2021 |
| Joseph Adams Ltd | Administrative & support | 2022 |
| JPM Publishing Limited | Information & communication | 2025 |
| JPS Online Limited | Administrative & support | 2003 |
| JR Property Development Ltd | Construction | 2017 |
| JRD Boilers Limited | Construction | 2021 |
| JS Autowrx Ltd | Manufacturing | 2025 |
| JSC Cotswold Design and Build Ltd | Construction | 2022 |