| J.G Sparx Limited | Construction | 2016 |
| J.L. Dycha Ltd | Transport & logistics | 2022 |
| J.M. Kamau Limited | Construction | 2014 |
| J.O.Adams & SON Limited | Agriculture & fishing | 1955 |
| J.O.S.P Logistics Limited | Transport & logistics | 2007 |
| J.P.W. Limited | Manufacturing | 1999 |
| J.R Interiors (UK) Ltd | Construction | 2014 |
| J.R's Southern Twist Ltd | Wholesale & retail | 2025 |
| J.R. Watson & Co | | 1995 |
| J.S.W.Da'Rus Ltd | Transport & logistics | 2024 |
| J.T.Raca International Limited | Manufacturing | 1998 |
| J.W. Turner Limited | Construction | 1962 |
| J.W.Hughes Building Contractors Ltd | Construction | 2001 |
| J.W.R. Construction Limited | Construction | 1989 |
| J123ESH Ltd | Real estate | 2026 |
| J2 Property Group Limited | Real estate | 2022 |
| J22K Ltd | Construction | 2025 |
| J50K Recovery Services Limited | Transport & logistics | 2014 |
| J7 GAS, Heating & Plumbing Ltd | Construction | 2025 |
| J9 Electrical Services Limited | Construction | 2024 |
| JA Global Ltd | Wholesale & retail | 2015 |
| JA Global Traders Limited | Wholesale & retail | 2023 |
| JAB Spares Limited | Wholesale & retail | 2015 |
| Jabata Healthcare Limited | Health & social care | 2018 |
| Jabelectronics Ltd | Wholesale & retail | 2025 |
| JAC Creative Services Ltd | Arts & recreation | 2017 |
| Jaccoud Engineering Limited | Professional & scientific | 2025 |
| Jack & Co Developments Ltd | Construction | 2024 |
| Jack James Cleaning Services Ltd | Administrative & support | 2024 |
| Jack Joseph Properties Limited | Real estate | 2020 |
| Jack Kirby Estates Ltd | Real estate | 2025 |
| Jackie Muscat Ltd | Information & communication | 2019 |
| Jackson & Grimes Limited | Professional & scientific | 1999 |
| Jackson Blason Hunt Ltd | Professional & scientific | 2013 |
| Jackson Grundy Financial Services Limited | Financial services | 2002 |
| Jackson Management Services Ltd | Hospitality | 2025 |
| Jackson Stone Design Ltd | Manufacturing | 2019 |
| Jacksons Diesel Centre Ltd | Wholesale & retail | 2013 |
| Jackson’S Dog Grooming Ltd | Other services | 2023 |
| Jacob & Olivia Ltd | Professional & scientific | 2025 |
| Jacob Lilly Limited | Wholesale & retail | 2017 |
| Jacob Warren Constructions Limited | Construction | 2025 |
| Jacs Property Investment Ltd | Real estate | 2026 |
| Jacsac Properties Limited | Real estate | 2008 |
| JAD Denham Properties Ltd | Real estate | 2024 |
| JAD Networks Ltd | Information & communication | 2019 |
| Jade Pavilion Limited | Hospitality | 2016 |
| Jadealexanderconrad Limited | Administrative & support | 2013 |
| Jadeda Clothings Ltd | Wholesale & retail | 2024 |
| Jaedel Limited | Health & social care | 2014 |
| Jaez House Ltd | Real estate | 2024 |
| Jafri Legal Limited | Professional & scientific | 2026 |
| JAG Consulting Limited | Professional & scientific | 2025 |
| Jag-Tec Limited | Transport & logistics | 2001 |
| Jaguar Waste Services LLP | | 2025 |
| Jagy Properties Ltd | Administrative & support | 2023 |
| Jahirah Investment Company Limited | Real estate | 2020 |
| Jaibird Photography Ltd | Professional & scientific | 2023 |
| Jaims Advanced Inspection & Measurement Solutions Ltd | Professional & scientific | 2025 |
| Jain Consultancy Limited | Health & social care | 2019 |
| Jaineel Supply Chain & Solution Ltd | Wholesale & retail | 2023 |
| Jairaj Investments & Properties Limited | Professional & scientific | 1992 |
| Jaja Grocery Store Ltd | Wholesale & retail | 2019 |
| JAK Haulage Limited | Transport & logistics | 2024 |
| Jake Hughes Racing Limited | Arts & recreation | 2012 |
| Jakhu Services Ltd | Wholesale & retail | 2021 |
| Jaks (Kings Road) Limited | Hospitality | 2012 |
| Jaks Mayfair Limited | Hospitality | 2015 |
| Jaks Place Limited | Hospitality | 2011 |
| Jaku Construction Ltd | Construction | 2021 |
| Jalba Building Ltd | Construction | 2025 |
| Jalfrayzi Ltd | Hospitality | 2025 |
| Jalfry Ltd | Hospitality | 2020 |
| JAM House 1 Limited | Hospitality | 2014 |
| JAM House Entertainment Limited | Financial services | 2014 |
| JAM Sport (UK) Ltd | Wholesale & retail | 2007 |
| James Agnew Consultants Ltd | Financial services | 2019 |
| James and James Fulfilment Ltd | Transport & logistics | 2010 |
| James and James Holdings Limited | Transport & logistics | 2017 |
| James Anthony Estate Agents Limited | Real estate | 2012 |
| James Anthony Group Ltd | Financial services | 2017 |
| James Anthony Land and New Homes Ltd | Real estate | 2017 |
| James Anthony Lettings Ltd | Real estate | 2017 |
| James Askew Ltd | Information & communication | 2018 |
| James Butler Limited | Arts & recreation | 1977 |
| James Clark & Associates Ltd | Information & communication | 2017 |
| James Clayson Property Ltd | Real estate | 2013 |
| James D Carpentry and Joinery Ltd | Manufacturing | 2018 |
| James King (Plant) Limited | Administrative & support | 1989 |
| James Littlejohn Consultancy Ltd | Professional & scientific | 2016 |
| James Peel Consulting Limited | Professional & scientific | 2025 |
| James Platt Associates Ltd | Professional & scientific | 2019 |
| James Rose Estates and Homes Ltd | Real estate | 2025 |
| James Whittemore Golf Limited | Arts & recreation | 2022 |
| Jameshickman Ltd | Construction | 2019 |
| Jamie Mitchell Services Ltd | Wholesale & retail | 2026 |
| Jamsport Media Ltd | Information & communication | 2021 |
| Jamsport Racing (UK) Limited | Wholesale & retail | 2018 |
| Jamus Services Limited | Health & social care | 2015 |
| Janbarree Limited | Education | 2000 |