| IRC Nets & Ropes Ltd | Manufacturing | 2024 |
| Iron Hoop Properties Ltd | Real estate | 2016 |
| Ironmongery Warehouse Limited | Wholesale & retail | 2017 |
| Irvine Ventures Ltd | Information & communication | 2026 |
| Isaac Noah Limited | Information & communication | 2014 |
| ISC Homes Limited | Construction | 2017 |
| Isla Noir Ltd | Wholesale & retail | 2025 |
| Ispcare Ltd | Health & social care | 2024 |
| Istaqlal Ltd | Hospitality | 2026 |
| IT 123 Limited | Information & communication | 2021 |
| Itech Electrical Group Ltd | Construction | 2021 |
| ITM Alesha Ltd | Wholesale & retail | 2025 |
| ITS4 Ltd | Extraterritorial | 2007 |
| Ivona Ltd | Households | 2019 |
| J & J Inc. Ltd. | Wholesale & retail | 2010 |
| J Ball Facilities Ltd | Professional & scientific | 2025 |
| J Hartland Properties Ltd | Real estate | 2025 |
| J Hurst Consultancy Ltd | Administrative & support | 2023 |
| J T Mechanical Services Limited | Construction | 2003 |
| J W Hardwick & Sons Limited | Administrative & support | 2008 |
| J&J Healthcare Epsom Ltd | Health & social care | 2021 |
| J&J Thai Massage and Beauty Limited | Other services | 2024 |
| J. Stoneman and Sons Limited | Other services | 1937 |
| J.B.J. (Techniques) Limited | Manufacturing | 1974 |
| J.D.King Carpentry Ltd | Manufacturing | 2019 |
| J.Dodson Ltd | Manufacturing | 2022 |
| J.R.Peterson Ltd | Information & communication | 2020 |
| Jabaquara 2 Ltd | Professional & scientific | 2024 |
| Jabaquara Consulting Ltd | Professional & scientific | 2024 |
| JAM Capital Investments Limited | Financial services | 2024 |
| Jamel Solutions Limited | Information & communication | 2023 |
| James Barr Design Ltd | Professional & scientific | 2014 |
| James Building Company Ltd | Construction | 2022 |
| James Fitzwalter Ltd | Real estate | 2020 |
| James Paul Electrical Ltd | Construction | 2020 |
| Jammie Properties Ltd | Real estate | 2021 |
| Jamok Limited | Hospitality | 2018 |
| Jamtech Limited | Information & communication | 2007 |
| Janes Construction Ltd | Construction | 2026 |
| Jarvi Transport Ltd | Transport & logistics | 2024 |
| Jawa Curry House Limited | Hospitality | 2023 |
| Jay-Bal -Health Care Services Ltd | Health & social care | 2025 |
| Jayghaer Pierre Ltd | Wholesale & retail | 2021 |
| Jayserv Mechanical & Electrical Limited | Construction | 2017 |
| JBO (Kent) Ltd | Professional & scientific | 2023 |
| JCM Limited | Professional & scientific | 2003 |
| JDW Landscaping Limited | Construction | 2025 |
| JED Contractors Ltd | Construction | 2020 |
| Jedris Limited | Construction | 2004 |
| Jedris Mill Limited | Construction | 2009 |
| Jedrison Limited | Construction | 2008 |
| Jeff INT Ltd | Transport & logistics | 2012 |
| JEI Future Technologies Limited | Professional & scientific | 2024 |
| Jenb Limited | Construction | 2024 |
| Jenga (Building Consultants) Limited | Real estate | 1960 |
| Jenga Holdings Limited | Financial services | 1965 |
| Jenga(Golf Club Holding)Limited | Real estate | 1964 |
| Jennifer Mortimer Limited | Wholesale & retail | 2017 |
| Jesbel Planners Ltd | Hospitality | 2025 |
| Jessaar Ltd | Wholesale & retail | 2017 |
| JET Colours Ltd | Manufacturing | 2024 |
| JET Showroom Limited | Wholesale & retail | 2018 |
| Jewel Cars Gatwick Ltd | Transport & logistics | 2011 |
| JF Squad Stitch and Beauty Limited | Other services | 2026 |
| JFJ Property Investments Ltd | Households | 2024 |
| JFK Services Limited | Other services | 2017 |
| Jgps Consulting LLP | | 2016 |
| Jiant Productions Ltd | Information & communication | 2022 |
| Jiant Social Media Ltd | Extraterritorial | 2022 |
| Jiants Hierarchy Ltd | Financial services | 2026 |
| Jijo Group Ltd | Hospitality | 2018 |
| JIM Trans Limited | Other services | 2015 |
| JJB BMS Limited | Construction | 2013 |
| Jjhr Holdings Limited | Financial services | 2023 |
| JK Nail & Beauty Ltd | Other services | 2009 |
| JKS Surveyors Ltd | Professional & scientific | 2020 |
| JMB Socials Ltd | Information & communication | 2025 |
| Jmeare Fitness Ltd | Health & social care | 2020 |
| JNN Services Limited | Professional & scientific | 2026 |
| Jnri (Southern) Ltd | Information & communication | 2024 |
| Jnri Limited | Information & communication | 2007 |
| Jnus Associates Ltd | Information & communication | 2018 |
| JO Hills Consulting Ltd | Professional & scientific | 2025 |
| JO Squared Management Ltd | Construction | 2017 |
| JOE to Go Limited | Manufacturing | 2023 |
| Jogc Ltd | Wholesale & retail | 2023 |
| Jogilvie Limited | Administrative & support | 2023 |
| John Brumwell Administration Limited | Financial services | 1966 |
| John Chiverton Associates Limited | Administrative & support | 1978 |
| Johnsons (Park Royal) Limited | Construction | 1979 |
| Johnston Court Residents Limited | Households | 2009 |
| Joiners Meadow Management Limited | Households | 1974 |
| Joint Venture Property Ltd | Real estate | 2021 |
| Jokpitan Health Care Limited | Health & social care | 2018 |
| Jolly Brickmakers Limited | Hospitality | 2014 |
| Jonesfilm Motion Pictures Limited | Information & communication | 2013 |
| Joseph & Stacey Homes Ltd | Real estate | 2017 |
| Joseph Edward Electrical Ltd | Construction | 2026 |
| Josh and Susie Bailey Limited | Extraterritorial | 2016 |
| Joshua Franklin Engineering Systems Ltd | Information & communication | 2022 |