| Internal Audit Consulting Limited | Professional & scientific | 2012 |
| Internexus Ltd | Wholesale & retail | 2025 |
| Interspace Industries Limited | Professional & scientific | 1998 |
| Inventures 100 Ltd | Professional & scientific | 2016 |
| ION Dreams Ltd | Information & communication | 2025 |
| Iplate Solutions Limited | Information & communication | 2014 |
| Irems Ltd | Wholesale & retail | 2025 |
| Isabel Dominguez Limited | Professional & scientific | 2010 |
| Isabel Hospice Limited | Health & social care | 1995 |
| Isabel Hospice Trading Limited | Wholesale & retail | 1989 |
| ISB Commercial Services Limited | Professional & scientific | 2018 |
| Istanbul Grooming Room Ltd | Other services | 2016 |
| Istoc Limited | Wholesale & retail | 2024 |
| ITD 2000 Limited | Education | 2023 |
| ITS OK Property Limited | Real estate | 2024 |
| Ivor Partridge & Son(Begbroke)Limited | Professional & scientific | 1944 |
| IVY Apps Ltd | Information & communication | 2024 |
| IVY Smile Clinic Ltd | Health & social care | 2020 |
| Izan WGC Ltd | Hospitality | 2026 |
| J & D Resources Ltd | Real estate | 2018 |
| J & L Property Maintenance Services Ltd | Administrative & support | 2010 |
| J & S Funeral Service Limited | Other services | 2009 |
| J K Minerva LLP | | 2016 |
| J L H Financial Consultancy Limited | Professional & scientific | 2005 |
| J Marsh Plumbing Services Limited | Administrative & support | 2018 |
| J N T Autocare Ltd | Wholesale & retail | 2024 |
| J R Scaffolding (Hitchin) Ltd | Construction | 2016 |
| J&J(Uk)Consulting Limited | Other services | 2019 |
| J&R Property Developments Ltd | Construction | 2019 |
| J. Sherriff Farming Limited | Agriculture & fishing | 2009 |
| J.D.Whisker Limited | Wholesale & retail | 1958 |
| J4HERTS Ltd. | Other services | 2018 |
| Jack Gajjar Electrical Ltd | Construction | 2023 |
| JAL Practitioner Limited | Health & social care | 2019 |
| James Knopp VFX Limited | Information & communication | 2016 |
| Jarrards Limited | Construction | 1974 |
| Jasperjane Limited | Education | 2015 |
| Jaycee Partnership Ltd | Financial services | 2015 |
| Jaydc Limited | Administrative & support | 2009 |
| Jaydeva Ltd | Professional & scientific | 2023 |
| Jaylambda Ltd | Professional & scientific | 2015 |
| Jaytooley Limited | Construction | 2013 |
| Jbrooks Group Ltd | Arts & recreation | 2025 |
| JC Digital Products Limited | Information & communication | 2024 |
| JC Garden Services Herts Limited | Administrative & support | 2025 |
| JC Softlinks Ltd | Information & communication | 2018 |
| Jcal Limited | Real estate | 1971 |
| JCE Engineering Works Limited | Construction | 2021 |
| JCN Cleaning Facility Management Ltd | Administrative & support | 2018 |
| JD Vehicle Repair Ltd | Wholesale & retail | 2022 |
| JDB Enterprise Group Ltd | Financial services | 2011 |
| JDP Consultancy Ltd | Professional & scientific | 2009 |
| JED Equity Deals Ltd | Real estate | 2025 |
| Jenisha Enterprise Private Ltd | Wholesale & retail | 2025 |
| Jenkins Industries Ltd | Hospitality | 2022 |
| Jenmor Hospitality Ltd | Hospitality | 2026 |
| Jenmor Property Limited | Real estate | 2024 |
| Jenny Lash Couture Limited | Other services | 2025 |
| Jeol(U.K.)Limited | Wholesale & retail | 1968 |
| JET Blast LLP | | 2017 |
| JGS IT Services Ltd | Information & communication | 2025 |
| JIN Zhong Properties Ltd | Real estate | 2023 |
| JJ Electrics JJ Ltd | Construction | 2021 |
| Jjpp Limited | Real estate | 2025 |
| Jkent Security (JKS) Ltd | Other services | 2024 |
| JMP Consulting Engineers Ltd | Construction | 2019 |
| JN Partnership Ltd | Wholesale & retail | 2026 |
| Jocam Ltd | Information & communication | 2023 |
| Jockney Media Limited | Information & communication | 2020 |
| John G. Lake Ministries UK & IE Ltd | Other services | 2015 |
| John Waters of Ware Limited | Manufacturing | 2003 |
| Joint PUB Ventures Ltd | Administrative & support | 2023 |
| Jointing Solutions Ltd | Construction | 2025 |
| Jolerikeem Ltd | Professional & scientific | 2019 |
| Jonogo Ventures Limited | Wholesale & retail | 2025 |
| Jordie Limited | Extraterritorial | 2023 |
| Joseph Hale Consultancy Limited | Professional & scientific | 2016 |
| Journey Internet Limited | Information & communication | 2023 |
| JP Cloud Services Ltd | Information & communication | 2025 |
| JP Express Delivery Limited | Transport & logistics | 2025 |
| JQ Exports Limited | Wholesale & retail | 2025 |
| JQ Fashion Trading Ltd | Wholesale & retail | 2025 |
| JQT Services Ltd | Health & social care | 2018 |
| JRM Mobile-Tech Ltd | Manufacturing | 2023 |
| JRS IT Consulting Ltd | Information & communication | 2022 |
| Jrstoregoods Ltd | Wholesale & retail | 2026 |
| JS Green Waste Limited | Other services | 2020 |
| JS Learning Solutions Ltd | Professional & scientific | 2022 |
| JSP Prime Investment Ltd | Real estate | 2025 |
| Jsper Software Limited | Information & communication | 2025 |
| JTP Trading Limited | Wholesale & retail | 2024 |
| Jueeri Ltd | Manufacturing | 2022 |
| Julia Roberts Advisory Ltd | Professional & scientific | 2025 |
| July Group Limited | Professional & scientific | 2009 |
| Jumanta Ltd | Transport & logistics | 2014 |
| Just Coaching Academy Limited | Arts & recreation | 2024 |
| Just Imagine Day Nursery Limited | Education | 2012 |
| Just Imagine Nurseries - ALL Saints Ltd | Health & social care | 2018 |
| Just Imagine Nurseries - Colchester Academy Ltd | Health & social care | 2017 |
| Just Imagine Nurseries - Vange Ltd | Health & social care | 2016 |