| Ismailfaqirzai Ltd | Wholesale & retail | 2024 |
| IT & Marketing Co-Op Ltd | Information & communication | 2026 |
| IT & T Consulting Limited | Information & communication | 2005 |
| IT Corporate Ltd | Information & communication | 2016 |
| IT Courier Drivers Ltd | Administrative & support | 2017 |
| Italian Light Store Limited | Wholesale & retail | 2026 |
| Itonion Ltd | Wholesale & retail | 2024 |
| Itsolutionist Limited | Information & communication | 2024 |
| IVA Kiddie Ventures Ltd | Health & social care | 2015 |
| Ivanhurst Property Development Company Limited | Real estate | 2006 |
| Ives Property Holdings Limited | Construction | 1972 |
| Ivory & Castle Property Services Ltd | Real estate | 2022 |
| Iwan FON Estate Agents Limited | Real estate | 2026 |
| Ixoraa Ltd | Information & communication | 2021 |
| Ixxi Limited | Health & social care | 2024 |
| IYG Carpentry Ltd | Construction | 2015 |
| J & G Solar Maintenance Ltd | Administrative & support | 2021 |
| J & K Computer Services Limited | Professional & scientific | 2000 |
| J & S Wilkinson Services Ltd | Transport & logistics | 2007 |
| J a Contracts Limited | Water & waste | 2007 |
| J C Alexanders Limited | Information & communication | 2004 |
| J D Kendall Limited | Administrative & support | 1999 |
| J H T Electrical Contractors Limited | Construction | 2002 |
| J J Properties (London) Ltd. | Real estate | 2004 |
| J L Haulage and SON Ltd | Transport & logistics | 2004 |
| J R Accountancy Services Ltd | Professional & scientific | 2002 |
| J R C Business Consultants Limited | Professional & scientific | 1998 |
| J R D Enterprises Limited | Real estate | 1994 |
| J R Islam Property Ltd | Real estate | 2021 |
| J Torres Limited | Wholesale & retail | 2005 |
| J Turner Associates Ltd | Construction | 2003 |
| J W Stones Ltd | Wholesale & retail | 2020 |
| J&S Facilities Limited | Administrative & support | 2013 |
| J&Ssolutions Ltd | Wholesale & retail | 2022 |
| J'S Caribbean EAT OUT Limited | Hospitality | 2017 |
| J. & M. Distribution Limited | | 1985 |
| J. Barr Electrical Ltd | Construction | 2002 |
| J. Brand & Sons Property Development Ltd | Real estate | 2002 |
| J. Curtis (Comfort Shoes) Limited | Transport & logistics | 1947 |
| J. F. Jones Ltd | Administrative & support | 2001 |
| J. FOX Futures Limited | Financial services | 2007 |
| J. J. Sullivan & SON Limited | | 1975 |
| J. Moore & SON Limited | | 1980 |
| J. Rawal Ltd | Health & social care | 1995 |
| J. Reed Accountants Limited | Professional & scientific | 2005 |
| J. Reeder Lock & Safe Co. Limited | Administrative & support | 1975 |
| J. Shanahan Limited | Construction | 2003 |
| J. V. Carpets Limited | Wholesale & retail | 1982 |
| J. Whitham and Company Limited | | 1968 |
| J.A. Dawes Engineering Limited | Manufacturing | 1978 |
| J.B. Jones Decorators Limited | Construction | 2004 |
| J.B. Russell Engineers Limited | Manufacturing | 1966 |
| J.Bennett & Son(Printers)Limited | | 1962 |
| J.D. Robertson & Co. Limited | Wholesale & retail | 1987 |
| J.D.Investments Limited | Real estate | 1950 |
| J.E. Tann Merioneth & District Properties Limited | | 1978 |
| J.E.L Property Group Limited | Real estate | 2026 |
| J.H. Vince Plumbing & Heating Limited | Construction | 2002 |
| J.H.& T.P.Duncan Limited | Other services | 1947 |
| J.J. Construction Limited | | 1986 |
| J.J.Property Management 1987 (Walton &Frinton) Limited | | 1987 |
| J.Livermore & Sons Limited | Other services | 1960 |
| J.M. Builders Merchants Limited | Wholesale & retail | 1983 |
| J.N.B. Electrical Engineers Ltd | Construction | 2003 |
| J.P. Poulter Limited | | 1982 |
| J.R.S. Properties Limited | Construction | 2001 |
| J.W.D. Group Limited | | 1988 |
| J.W.R. Developments Limited | | 1985 |
| J.W.R. Shopfitters Limited | | 1981 |
| JA Digital Commerce Limited | Wholesale & retail | 2025 |
| Jab&Co PVT Ltd | Wholesale & retail | 2021 |
| Jacemar Ltd | Wholesale & retail | 2026 |
| Jacken Design Limited | | 1974 |
| Jacks Centre Latchingdon Bowls Club | Arts & recreation | 1993 |
| Jacks Stores Ltd | Wholesale & retail | 2023 |
| Jackson Square Partners Limited | Financial services | 2019 |
| Jacksonian Wellbeing Service Ltd | Health & social care | 2024 |
| Jacmac Property Services Ltd | Real estate | 2025 |
| Jacmeg Electrical Limited | Wholesale & retail | 1998 |
| JAD Properties Limited | Real estate | 2017 |
| Jadeg Ltd | Wholesale & retail | 2026 |
| Jademech Ltd | Real estate | 2007 |
| Jaff Holding Ltd | Administrative & support | 2022 |
| Jaffna Java Limited | Hospitality | 2025 |
| Jaimex Ltd | Administrative & support | 2004 |
| Jalebee Limited | Extraterritorial | 2000 |
| James Carter Properties Limited | Real estate | 2004 |
| James Christopher Gibb Enterprises Limited | | 1984 |
| James Development Company Limited | Construction | 1959 |
| James Hair & Beauty Ltd | Wholesale & retail | 2025 |
| James Hawes(Manor Park and Romford)Limited | Other services | 1939 |
| James James Developments Limited | Wholesale & retail | 1986 |
| James Kavanagh & Co Ltd | Construction | 2020 |
| Jamie MOY Commissioning Services Limited | Other services | 2017 |
| Jamila KH Limited | Wholesale & retail | 2024 |
| Jane Burton Traditional Flooring | | 2006 |
| Jangles Limited | Information & communication | 1997 |
| Janus Contract Services Ltd. | Manufacturing | 1997 |
| Jardine Press Ltd | Information & communication | 2002 |
| Jarvis Electrical Contractors Ltd | Administrative & support | 2007 |