| J Hilton Traffic Management Ltd | Construction | 2025 |
| J L Thompson Limited | Other services | 2011 |
| J Palanisamy Limited | Information & communication | 2019 |
| J Rose Design Limited | Arts & recreation | 2009 |
| J Staley (Stonework) Limited | Construction | 2002 |
| J Turner Property Limited | Real estate | 2025 |
| J W Ayre Joinery Limited | Construction | 2026 |
| J W Blanchard (Properties) Limited | Wholesale & retail | 1986 |
| J W Structural Components Ltd | Other services | 2021 |
| J Wright Wind Ltd | Manufacturing | 2022 |
| J&A Professional Services Ltd | Other services | 2015 |
| J&G Italian Limited | Hospitality | 2018 |
| J. R. Wilkinson & Sons Limited | Construction | 2002 |
| J. Rouch Consulting Limited | Professional & scientific | 2020 |
| J.A. Earle (Farms) Limited | Agriculture & fishing | 1996 |
| J.D. Propitup Limited | Information & communication | 2015 |
| J.E.G. Transport Ltd | Transport & logistics | 2023 |
| J.L. Greenwood (Property) Ltd | Real estate | 2026 |
| J.L. Greenwood Ltd | Construction | 2019 |
| J.P. Coyne Limited | Construction | 2017 |
| J.P. Murphy & Sons Ltd | Real estate | 2020 |
| J3 Estates Ltd | Real estate | 2020 |
| J4 Enterprise Ltd | Professional & scientific | 2025 |
| Jacaranda Ventures Limited | Financial services | 2014 |
| Jack Brough Ltd | Professional & scientific | 2025 |
| Jacksons Beauty Ltd | Other services | 2024 |
| Jacoubs Takeaway Limited | Hospitality | 2025 |
| Jacren Consulting Limited | Professional & scientific | 2017 |
| JAD Strategy & Coaching Ltd | Professional & scientific | 2019 |
| JAI Shutters Ltd | Manufacturing | 2018 |
| Jaibelle Limited | Health & social care | 2021 |
| Jake Ardley Limited | Professional & scientific | 2025 |
| Jake Phipps Limited | Other services | 2012 |
| Jakidom Ltd | Information & communication | 2018 |
| Jamax Holdings Ltd | Professional & scientific | 2007 |
| James Bond First Editions Ltd | Wholesale & retail | 2020 |
| James Burke Joinery Limited | Construction | 2016 |
| James D Ltd | Information & communication | 2024 |
| James Dean Associates Limited | Professional & scientific | 2020 |
| James Herbert & Sons Building Contractors & Developers Limited | Construction | 1991 |
| James Holdings (YS) Limited | Financial services | 2025 |
| James Lloyd Associates Limited | Administrative & support | 2009 |
| James Oscar Ltd | Information & communication | 2014 |
| James Property Group (YS) Limited | Real estate | 2024 |
| James Waste Commercial LLP | | 2020 |
| James Waste Management LLP | | 2009 |
| Jamie Buchan Wealth Management Limited | Financial services | 2012 |
| Jane Banister Limited | Professional & scientific | 2010 |
| Jane Wicks Consultancy Limited | Other services | 2009 |
| Jango Communications Limited | Professional & scientific | 2001 |
| Jangocomms Limited | Professional & scientific | 2020 |
| Janitorial Supplies Direct UK Ltd | Administrative & support | 2018 |
| Januscd Limited | Real estate | 2007 |
| JAS Solutions Limited | Information & communication | 2024 |
| Jasmine Construction Limited | Construction | 2025 |
| Jay's Bakery GG Limited | Wholesale & retail | 2025 |
| Jay's Bakery KEW Limited | Wholesale & retail | 2025 |
| Jaytech Blue Ltd | Information & communication | 2011 |
| JB Beauty (Richmond) Limited | Other services | 2026 |
| JB Fintech Solutions Ltd | Information & communication | 2025 |
| JB Grill Foods Limited | Hospitality | 2021 |
| JB Holdings (Halnaby) Limited | Financial services | 2025 |
| JC Creative Ltd | Professional & scientific | 2020 |
| JCF Properties Ltd | Real estate | 2015 |
| JDI Distributions Ltd. | Wholesale & retail | 2021 |
| Jeffrie Property Co Ltd | Real estate | 2019 |
| Jelly Butterfingers Limited | Manufacturing | 2025 |
| Jeplee Ltd | Construction | 2021 |
| Jerone Henry TM Ltd | Construction | 2024 |
| Jessica ET Michel Limited | Hospitality | 2004 |
| Jestanoff Ltd | Information & communication | 2017 |
| JET Cars Limited | Transport & logistics | 2018 |
| JET Coaches Ltd | Transport & logistics | 2020 |
| Jewel Aviation and Technology Ltd | Transport & logistics | 2003 |
| JF Technology (UK) Ltd | Information & communication | 1998 |
| Jhana Ltd | Wholesale & retail | 2020 |
| Jhanavi Diagnostics Ltd | Health & social care | 2025 |
| Jhet Advisory Limited | Professional & scientific | 2018 |
| Jianglakawa Limited | Manufacturing | 2026 |
| Jigsaw Childcare Richmond Limited | Professional & scientific | 2015 |
| JIN Jewellery Limited | Wholesale & retail | 2017 |
| Jinri Real Estate Ltd | Construction | 2018 |
| Jinwei Ltd | Hospitality | 2021 |
| JJ Health Limited | Health & social care | 2023 |
| JJF Commercial Services Limited | Professional & scientific | 2014 |
| JJH & Co Holdings Ltd | Financial services | 2021 |
| JK Paid Search Limited | Professional & scientific | 2016 |
| JKA GB Limited | Arts & recreation | 2005 |
| JKD Plumbing Ltd | Construction | 2025 |
| JKL Property Management Services Limited | Administrative & support | 2017 |
| JL Architects Limited | Professional & scientific | 2008 |
| JLB Consulting Limited | Professional & scientific | 2006 |
| JLB TM Ltd | Construction | 2020 |
| Jlnfilm Limited | Manufacturing | 2025 |
| JMB Risk Management Ltd | Financial services | 2019 |
| JMC Voutiras Investments Limited | Real estate | 2005 |
| JMD Business Supplies Limited | Administrative & support | 2013 |
| Jmoi Consultants Limited | Administrative & support | 2005 |
| Joar Ltd | Professional & scientific | 2022 |
| JOE & Co London Ltd | Information & communication | 2018 |