| IQ Digital Health Limited | Information & communication | 2018 |
| IQ Media Limited | Information & communication | 2002 |
| Iqon Consulting Ltd | Information & communication | 2025 |
| Iqra Dermatology Ltd | Health & social care | 2026 |
| IRD Ltd | Manufacturing | 2019 |
| Irro Limited | Administrative & support | 2016 |
| Irving Whitehouse Partners Limited | Professional & scientific | 1986 |
| Isaac Gill Limited | Health & social care | 2025 |
| Isbis LLP | | 2011 |
| ISE Holdings Ltd | Financial services | 2016 |
| Isee Properties Limited | Construction | 2012 |
| ISH Jewellery Limited | Manufacturing | 2025 |
| Isla E Consulting Ltd | Information & communication | 2021 |
| ISS Engineering Group Ltd | Wholesale & retail | 2018 |
| Istock Steel Limited | Extraterritorial | 2012 |
| IT - Ease Limited | Information & communication | 2004 |
| IT Advisory Solutions Ltd | Information & communication | 2023 |
| Italian LAB 3.0 Limited | Hospitality | 2014 |
| Itrs Partnerships Ltd | Administrative & support | 2026 |
| It’S SEW YOU Ltd | Wholesale & retail | 2025 |
| IUA Consulting Limited | Professional & scientific | 2023 |
| Ivory Cottage Ltd | Health & social care | 2018 |
| IW Project Management Consultancy Services Limited | Professional & scientific | 2014 |
| IWL Project & Property Services Ltd | Professional & scientific | 2025 |
| Iwop Ltd | Administrative & support | 2017 |
| J & G Global Welding & Fabricating Ltd | Professional & scientific | 2023 |
| J & Them Property Ltd | Real estate | 2021 |
| J B Structural Design Limited | Professional & scientific | 2017 |
| J Baker Holdings Ltd | Financial services | 2025 |
| J by K Limited | Other services | 2020 |
| J Fischer Ltd | Health & social care | 2010 |
| J R Bikes Limited | Wholesale & retail | 2015 |
| J Ratnasingham Anaesthesia Ltd | Health & social care | 2015 |
| J S K Lewis Limited | Health & social care | 2016 |
| J S Oldfield Ltd | Real estate | 2022 |
| J Stewart Consulting Ltd | Information & communication | 2023 |
| J Tomlinson Properties Ltd | Agriculture & fishing | 2010 |
| J V International Limited | Wholesale & retail | 2006 |
| J.W. Brocklehurst Limited | Other services | 2014 |
| J3J Consultancy Limited | Education | 2025 |
| J:Me Ventures Limited | Professional & scientific | 2024 |
| Jacked Structures Limited | Administrative & support | 2013 |
| Jackson Data Consulting Limited | Administrative & support | 2016 |
| Jackson Hughes Consulting Limited | Professional & scientific | 2014 |
| Jackson Hughes Management Limited | Households | 2014 |
| JAD Surgery Limited | Health & social care | 2021 |
| JAE Site Services Ltd | Professional & scientific | 2018 |
| JAG Electrical Services Ltd | Construction | 2020 |
| Jake Oregan Limited | Professional & scientific | 2026 |
| JAL Advisory Ltd | Financial services | 2020 |
| Jalal Asadis Ltd | Health & social care | 2023 |
| JAM Agent Limited | Wholesale & retail | 2010 |
| JAM Brands Ltd | Financial services | 2021 |
| James Hall Developments Limited | Construction | 2022 |
| James Hutchinson Arthroplasty Ltd | Health & social care | 2018 |
| James Rose Anaesthesia Limited | Health & social care | 2019 |
| Jamie Barnes Plastic Surgery Ltd | Health & social care | 2021 |
| Jamie Murray-Smith Limited | Information & communication | 2023 |
| Jams Planning Ltd | Professional & scientific | 2026 |
| Jamstd Limited | Real estate | 2014 |
| Jandeva Properties Limited | Real estate | 2017 |
| Jane Gorse Recruitment Limited | Other services | 2020 |
| Jane Hall Pilates Limited | Other services | 2006 |
| Jane Leitch Medical LLP | | 2025 |
| Jantzen Health Group Ltd | Health & social care | 2021 |
| Jantzen Investment Group Limited | Real estate | 2018 |
| JAR Limited | Real estate | 2024 |
| Jarvik Limited | Health & social care | 2022 |
| JAS Incorporated Limited | Financial services | 2021 |
| Jasmin Masih Ltd | Education | 2025 |
| Jason Coulston Interiors Limited | Professional & scientific | 2016 |
| Jaya Life LLP | | 2025 |
| Jays Drinks Limited | Wholesale & retail | 2025 |
| JB Anaesthesia Limited | Health & social care | 2019 |
| JB Brand Ltd | Professional & scientific | 2025 |
| JB DJ Ltd | Information & communication | 2021 |
| JB Dozen Records Ltd | Information & communication | 2025 |
| JB Marine Consulting Ltd | Professional & scientific | 2025 |
| Jbaa Medicine Limited | Health & social care | 2026 |
| Jbhp Limited | Administrative & support | 2025 |
| Jbsafe Ltd | Professional & scientific | 2023 |
| Jbsmith Consulting Ltd | Professional & scientific | 2025 |
| Jcds Leisure Limited | Hospitality | 2022 |
| JCM Resources Limited | Administrative & support | 2025 |
| JCO Strategies Limited | Information & communication | 2025 |
| JD Resin Flooring Ltd | Construction | 2026 |
| JDC Automobiles Limited | Wholesale & retail | 2019 |
| JDG Healthcare Limited | Health & social care | 2019 |
| JDS DIY Ltd | Wholesale & retail | 2016 |
| Jeannette Jackson Limited | Health & social care | 2011 |
| Jeevan Plastic Surgery Limited | Health & social care | 2019 |
| JEI Property Limited | Real estate | 2018 |
| JEM IT Solutions Ltd | Information & communication | 2025 |
| JEN Harrison Limited | Construction | 2019 |
| Jenkins Vascular Limited | Health & social care | 2020 |
| Jenny Brown Limited | Wholesale & retail | 2001 |
| Jenson Consulting Limited | Professional & scientific | 2025 |
| Jerico Group Ltd | Construction | 2023 |
| Jerico Properties Limited | Real estate | 2026 |
| JET Performance and Leadership Limited | Professional & scientific | 2023 |