| J a Hassell Plant Hire Limited | Wholesale & retail | 2003 |
| J B Brickwork Limited | Construction | 2007 |
| J Barnes Limited | | 1982 |
| J C Guildford Limited | Arts & recreation | 2007 |
| J Chan Ltd | Real estate | 2007 |
| J D K Contracting Ltd | Construction | 2007 |
| J J Paulman Contracts Limited | Administrative & support | 2006 |
| J J R Developments Ltd | Information & communication | 2003 |
| J K Property Portfolio Limited | Real estate | 2004 |
| J Miles & Co (Surveyor) | Professional & scientific | 1973 |
| J O Electrics Limited | Construction | 2003 |
| J P M Building Services Limited | Construction | 2007 |
| J T M (UK) Limited | Construction | 2003 |
| J&P Consultant Services Ltd | Construction | 2017 |
| J-M Capital Limited | Financial services | 2000 |
| J. a. Care Ltd | Health & social care | 2005 |
| J. Cadman Interiors Limited | Construction | 1986 |
| J. F. White Limited | Professional & scientific | 2007 |
| J. Kennedy Limited | Hospitality | 1936 |
| J. W. Educational Limited | Wholesale & retail | 1997 |
| J.Browne Properties (UK) Limited | Real estate | 2005 |
| J.D.Bell Ltd | Professional & scientific | 1996 |
| J.E.M. Services Limited | Administrative & support | 1981 |
| J.F.E. Associates Limited | Construction | 1988 |
| J.F.J.Langridge Limited | Construction | 1971 |
| J.H.Cooke & Sons Limited | Administrative & support | 1959 |
| J.J.P. Associates (Consultancy UK) Limited | Professional & scientific | 2003 |
| J.L. Jameson Limited | | 1937 |
| J.P. Automotive Limited | | 1976 |
| J.Par & Company Limited | Wholesale & retail | 1970 |
| J.R. Group & Associates Limited | | 1983 |
| J.R. Hodder (Plastics) Limited | | 1976 |
| J.W. Bros Construction Ltd | Construction | 2014 |
| J.W. Cannon & Co. (1948) Limited | Construction | 1996 |
| J.W. Mckenzie Limited | Construction | 2002 |
| J.W.Cannon & Co. Limited | Construction | 1962 |
| Jaan's Express Ltd | Wholesale & retail | 2022 |
| Jaaz Inc. Ltd | Construction | 2012 |
| JAC Systems Ltd | Professional & scientific | 2000 |
| Jackson Mark Consultancy Ltd | Professional & scientific | 2013 |
| Jackson Property Management London Limited | Real estate | 2021 |
| Jackson-Scott Associates Ltd | Professional & scientific | 2002 |
| Jadeneed Limited | Manufacturing | 1983 |
| Jado Properties Limited | Real estate | 1951 |
| JAI Deva Ltd | Hospitality | 2020 |
| JAK Sound Limited | Information & communication | 2006 |
| James French Trust Technique Limited | Education | 2005 |
| James Leighs Benz Services Ltd | Wholesale & retail | 2019 |
| James Murray Associates Limited | Financial services | 2005 |
| James W.Vincent(Flooring)Limited | Wholesale & retail | 1962 |
| James Walker Engineering Services Limited | Professional & scientific | 1979 |
| James Walker Moorflex Limited | Manufacturing | 1956 |
| James Walker Rotabolt Limited | Manufacturing | 1981 |
| James Walker Seals Limited | Professional & scientific | 1914 |
| James Walker Townson Limited | Manufacturing | 1989 |
| Jamesdean Limited | Real estate | 2004 |
| Jamie Mannan Ltd | Other services | 2019 |
| JAN H&C Property Management Limited | Real estate | 2022 |
| Janson Limited | Wholesale & retail | 2002 |
| Janush Property Ltd | Real estate | 2025 |
| Jarral Properties Ltd | Real estate | 2020 |
| Jason D'Souza Works Ltd | Other services | 2011 |
| Jason Keeley Limited | Other services | 2005 |
| Javelin Mosaic Limited | Professional & scientific | 2005 |
| Javision Ltd. | Information & communication | 1993 |
| JAY Maharaj Enterprise Ltd | Hospitality | 2025 |
| Jayes Investments Limited | Real estate | 2016 |
| Jaysport Ltd | Information & communication | 2007 |
| Jazmins Recruitment Ltd | Administrative & support | 2026 |
| JB Wealth Management Limited | Financial services | 1978 |
| JCL Frames Ltd | Construction | 2020 |
| JCM Futures Ltd | Real estate | 2025 |
| Jeakins Limited | Transport & logistics | 1994 |
| Jebco Exploration Inc. | | 1977 |
| Jehfa Ltd | Administrative & support | 2019 |
| Jenner House Limited | Households | 1996 |
| Jensen Accounting & Book-Keeping Services Limited | Professional & scientific | 2005 |
| Jeremy Johnson Consulting Limited | Professional & scientific | 2000 |
| Jesp Services Limited | Professional & scientific | 2000 |
| Jeyarani Ltd | Real estate | 2024 |
| Jeylux Construction Ltd | Construction | 2006 |
| JFK Computer Systems Limited | Information & communication | 2001 |
| Jidem Security (UK) Ltd. | Administrative & support | 2006 |
| Jiffle Limited | Information & communication | 2005 |
| Jigsaw (Croydon) Ltd | Education | 1999 |
| Jigsaw Developments Limited | Professional & scientific | 1987 |
| Jigsaw Education Holdings Limited | Financial services | 2023 |
| Jika Enterprises Ltd | Health & social care | 2007 |
| JIM Swanson Filming Limited | Information & communication | 2009 |
| Jimmer Motion Pictures Limited | Information & communication | 2023 |
| JJ Mobiles London Ltd | Wholesale & retail | 2022 |
| JJG Accounting Ltd | Professional & scientific | 2004 |
| JK Gold House & Fashion House Ltd | Wholesale & retail | 2004 |
| JK Nails Bar Limited | Other services | 2017 |
| JLP Innovation Ltd | Professional & scientific | 2015 |
| Jlrr Holdings Limited | Financial services | 2025 |
| Jlst Property Ltd | Real estate | 2020 |
| JMA Developments Limited | Construction | 2015 |
| JMA Management Consultancy Limited | Professional & scientific | 2017 |
| JMC Learning Ltd | Information & communication | 2007 |