| JK Construct Limited | Construction | 2013 |
| JK Gaming Limited | Information & communication | 2024 |
| JK Jones Developments Limited | Construction | 2021 |
| JK Property Ventures Ltd | Financial services | 2025 |
| JKA | | 2008 |
| JKX Executive Travel Ltd | Transport & logistics | 2018 |
| JL 18 Limited | Construction | 2018 |
| JLD Formwork Limited | Construction | 2020 |
| JLDP7 Promotions Limited | Arts & recreation | 2019 |
| JLG Powerpress Services Ltd | Professional & scientific | 2012 |
| JLP Lighting Limited | Construction | 2024 |
| JLR Legacy Properties Limited | Real estate | 2021 |
| JLS Installations (IOW) Ltd | Construction | 2025 |
| JM Blade Repairs Ltd | Manufacturing | 2023 |
| JM IT Consultancy Ltd | Information & communication | 2018 |
| JM07 Promotions Ltd | Arts & recreation | 2023 |
| JMB LAB Services Ltd | Professional & scientific | 2013 |
| JMB Property Limited | Real estate | 2025 |
| JMB Telecoms Ltd | Information & communication | 2026 |
| JMC Minerals LLP | | 2019 |
| JME Farrell Limited | Information & communication | 2013 |
| JMG (Pembs) Ltd | Construction | 2018 |
| JMG Convenience Store Ltd | Wholesale & retail | 2014 |
| JMG Flat Roofing South Wales Ltd | Construction | 2019 |
| JMG Roofing South Wales Ltd | Construction | 2017 |
| JMG Scaffolding South Wales Ltd | Construction | 2019 |
| JMH Construction and Civils Limited | Construction | 2019 |
| JMH Lighting Ltd | Construction | 2018 |
| JMI Construction and Civil Engineering Limited | Construction | 2014 |
| JMK Ace Limited | Health & social care | 2022 |
| JML Homes and Property Ltd | Real estate | 2026 |
| JML Renovations Limited | Construction | 2020 |
| Jmlittlejohns Ltd | Wholesale & retail | 2024 |
| JMP Drylining Ltd | Construction | 2024 |
| JMP Telecoms Limited | Information & communication | 2020 |
| JMV Properties Ltd | Real estate | 2019 |
| JMW Healthcare Services Ltd | Health & social care | 2025 |
| JO Wilson Fitness Limited | Arts & recreation | 2019 |
| Jo's Total TAN Ltd | Other services | 2011 |
| Joana Sena Ltd | Arts & recreation | 2025 |
| Joanna Court Management Company Limited | Households | 1987 |
| Joanne Beale Designs Ltd | Professional & scientific | 2026 |
| Joanne Peacock Aesthetics Ltd | Other services | 2024 |
| Joanne Peacock Medical Weight Loss Ltd | Health & social care | 2025 |
| JOD Property Company Ltd | Hospitality | 2014 |
| JOE Calzaghe Ltd | Arts & recreation | 2015 |
| Joel Dawe Limited | Construction | 2026 |
| John & Jane Ltd | Administrative & support | 2017 |
| John Benjamin Hair Co Ltd | Other services | 2018 |
| John Boxall & Sons Ltd | Construction | 2004 |
| John Calvert Consultancy Limited | Professional & scientific | 2013 |
| John E Snow Ltd | Administrative & support | 2014 |
| John Evans (Transport Services) Limited | Real estate | 1972 |
| John Francis Kusak Limited | Financial services | 2024 |
| John Gibson Management Limited | Real estate | 2019 |
| John Jeffery Care Limited | Real estate | 2025 |
| John Lloyd Orthopaedics Limited | Health & social care | 2014 |
| John Metcalf Ltd | Education | 2025 |
| John Nicholson Limited | Construction | 1988 |
| Johnboysgear Ltd | Wholesale & retail | 2025 |
| Johnson & Phillips (Capacitors) Limited | Manufacturing | 2013 |
| Johnson & Phillips (Holdings) Limited | Administrative & support | 2023 |
| Johnson & Phillips Limited | Energy | 2023 |
| Johnson Properties Ltd | Real estate | 2026 |
| Johnson's Lettings IW Ltd | Real estate | 2025 |
| Johnston R Limited | Wholesale & retail | 2022 |
| Joker 4 Transport Ltd | Transport & logistics | 2022 |
| JOMA5 Ltd | Real estate | 2020 |
| JON Brown Limited | Construction | 2004 |
| Jonathan Adams and Partners Architects Limited | Professional & scientific | 2013 |
| Jonathan Bethel Design Limited | Professional & scientific | 2021 |
| Jonathan Ryall Limited | Other services | 2020 |
| Jonathan Talks Photography Ltd | Professional & scientific | 2018 |
| Jonathan Terry Bathrooms Ltd | Construction | 2015 |
| Jones & Featherstone Carpentry Ltd | Manufacturing | 2017 |
| Jones Commercial Ltd | Real estate | 2010 |
| Jones Construction Management Limited | Construction | 2014 |
| Jones Family Eatery Limited | Hospitality | 2023 |
| Jones's Scaffolding Limited | Administrative & support | 2017 |
| Jonhire Limited | | 1983 |
| Joos Consultants Ltd | Professional & scientific | 2025 |
| Joosten Financial Planning Ltd | Financial services | 2016 |
| Joov Sports Products Limited | Manufacturing | 2019 |
| Jordan Hire Limited | Transport & logistics | 2010 |
| JORDAN22 Ltd | Wholesale & retail | 2019 |
| Jorden Valley Estates Limited | Extraterritorial | 2015 |
| Josefs Limited | Other services | 2008 |
| Josh Andrews Media Ltd | Information & communication | 2021 |
| Josh HTS Ltd | Wholesale & retail | 2026 |
| Josh Macrae Limited | Professional & scientific | 2024 |
| Jotpad Ltd | Wholesale & retail | 2025 |
| Joyceemma Ltd | Health & social care | 2014 |
| Joylicious Foods Limited | Wholesale & retail | 2016 |
| Joyner P. a. (Cymru) Limited | Construction | 1988 |
| Joys Travel Ltd | Transport & logistics | 2025 |
| JP & C Services Ltd | Manufacturing | 2026 |
| JP Dunn Services Limited | Administrative & support | 2016 |
| JP Grand Foods Ltd | Wholesale & retail | 2025 |
| JP International Holdings UK Limited | Wholesale & retail | 2020 |
| JP Logistics Solutions Limited | Transport & logistics | 1971 |