| J a Scoffham Ltd. | Construction | 2018 |
| J and J Commercials Limited | Transport & logistics | 1994 |
| J and R Leisure Limited | Hospitality | 2017 |
| J and T Agricultural Services Ltd | Administrative & support | 2012 |
| J and T Property Enterprises Limited | Administrative & support | 2012 |
| J B Construction & Carpentry Wales Limited | Construction | 2020 |
| J B H Property Investments Limited | Professional & scientific | 2014 |
| J B Souto Limited | Construction | 2023 |
| J B Transport Engineering Ltd | Administrative & support | 2016 |
| J Barton (Cardiff) Holdings Limited | Professional & scientific | 2010 |
| J Belcher Consultancy Limited | Professional & scientific | 2021 |
| J Boyes Ltd | Administrative & support | 2025 |
| J Brock & Sons Ltd | Wholesale & retail | 2018 |
| J C (Barrow) Limited | Financial services | 2014 |
| J C Direct Trading Limited | Wholesale & retail | 2018 |
| J C Technologies Limited | Information & communication | 2004 |
| J Carter Consultant Services Limited | Information & communication | 2015 |
| J Chadwick Illustration Ltd | Professional & scientific | 2015 |
| J Chauffeurs Ltd | Transport & logistics | 2021 |
| J Companys Ltd | Construction | 2022 |
| J D Filtration Limited | Administrative & support | 2018 |
| J D Property Management Services Ltd | Hospitality | 2024 |
| J D Renovations & Building Services Limited | Construction | 2021 |
| J E Fencing and Landscaping Limited | Administrative & support | 2023 |
| J E Ouston Consultants Limited | Professional & scientific | 2014 |
| J Ellery Properties Limited | Real estate | 2012 |
| J England Limited | Real estate | 2013 |
| J Eros Solutions Ltd | Information & communication | 2019 |
| J F Creations Ltd | Manufacturing | 2020 |
| J Ferrer Euro Ltd | Information & communication | 2025 |
| J G Francis Civil Engineering Ltd | Construction | 2006 |
| J G Mechanical Ltd | Professional & scientific | 2016 |
| J G Pristine Clean Ltd | Administrative & support | 2024 |
| J H M Assessments Ltd | Professional & scientific | 2016 |
| J H Services and Repairs Ltd | Wholesale & retail | 2024 |
| J Hallett Civils Limited | Construction | 2015 |
| J Hext Engineering Limited | Manufacturing | 2014 |
| J J Caravans Ltd | Wholesale & retail | 2018 |
| J J Morris Maintenance Limited | Other services | 2004 |
| J J Theobald Limited | Real estate | 2019 |
| J K Davies Limited | Other services | 2022 |
| J L PUB Company Ltd | Hospitality | 2016 |
| J L R Project Management Ltd | Construction | 2014 |
| J Lewis Performance Limited | Professional & scientific | 2026 |
| J Libra Two Ltd | Wholesale & retail | 2021 |
| J M Dental Limited | Health & social care | 2006 |
| J M G S P Consultancy Ltd | Professional & scientific | 2014 |
| J M Gill Financial Services Ltd | Financial services | 2019 |
| J M Walden Properties Limited | Real estate | 2012 |
| J MA Abba Ltd | Hospitality | 2020 |
| J Marko Property Limited | Hospitality | 2022 |
| J Nash Limited | Hospitality | 2024 |
| J Nixon Security Limited | Administrative & support | 2019 |
| J O Brown Ltd | Health & social care | 2021 |
| J O'Connell Construction Limited | Construction | 2019 |
| J O'Connor Services Ltd | Construction | 2018 |
| J Obrien Cladding Limited | Construction | 2017 |
| J Oliver Contractors Ltd | Construction | 2012 |
| J Oxley Design and Build Limited | Construction | 2014 |
| J P Hillier Limited | Professional & scientific | 2015 |
| J P J Games Limited | Information & communication | 2021 |
| J P Kenny Resources Ltd | Mining & quarrying | 2013 |
| J Pesticcio Developments Ltd | Construction | 2025 |
| J Petroleum Ltd | Wholesale & retail | 2025 |
| J Prime Ltd | Transport & logistics | 2019 |
| J Property Investment Ltd | Real estate | 2020 |
| J R Allen Limited | Health & social care | 2000 |
| J R Films Limited | Information & communication | 2012 |
| J R Lane Limited | Health & social care | 2007 |
| J R M Flat Roofing Specialists Ltd | Construction | 2019 |
| J R Stringer Limited | Construction | 2023 |
| J R Velasco Dental Prosthetics Limited | Health & social care | 2022 |
| J S (Cardiff) Properties Ltd | Real estate | 2025 |
| J S Weber & Company Limited | Professional & scientific | 2003 |
| J Shahid Ltd | Financial services | 2017 |
| J Shaw Consulting Ltd | Professional & scientific | 2017 |
| J Smith Auto Sales Ltd | Wholesale & retail | 2019 |
| J Smith Maintenance Services Ltd | Construction | 2023 |
| J Speakman Pharm Ltd | Wholesale & retail | 2023 |
| J Stoddart Limited | Health & social care | 2016 |
| J Syndicate Holdings Limited | Financial services | 2025 |
| J T Coles Limited | Construction | 2025 |
| J T Molloy Limited | Construction | 2017 |
| J T Tree Services Ltd | Administrative & support | 2019 |
| J Taylor Homes Ltd | Real estate | 2025 |
| J Thomas Property Ltd | Real estate | 2021 |
| J UK Designs Ltd | Professional & scientific | 2019 |
| J V Developments Limited | Real estate | 2016 |
| J W Bassett Pubs and Bars Limited | Hospitality | 2003 |
| J W Homes Financial Services Limited | Financial services | 2012 |
| J W Peace Limited | Other services | 2016 |
| J Welsh Carpentry Limited | Construction | 2002 |
| J West Plastering Ltd | Construction | 2022 |
| J White Holdings Ltd | Financial services | 2020 |
| J White Plastering Ltd | Construction | 2025 |
| J&B Estate Group Ltd | Hospitality | 2025 |
| J&C Business (UK) Co., Limited | Professional & scientific | 2012 |
| J&C Dragon Limited | Hospitality | 2026 |
| J&C Logistics Group Ltd | Transport & logistics | 2025 |
| J&J Compliance Ltd | Administrative & support | 2017 |