| JEL Property Holdings Limited | Real estate | 2024 |
| Jelful Limited | Wholesale & retail | 2025 |
| JEM Industrial Services Ltd | Administrative & support | 2026 |
| JEM Travels Ltd | Transport & logistics | 2024 |
| Jemc Projects Ltd | Real estate | 2024 |
| Jenaiah Limited | Administrative & support | 2025 |
| Jenesys Associates Limited | Professional & scientific | 2006 |
| Jenkins and Lock Property Services Ltd | Construction | 2023 |
| Jenkins and Thomas Properties Ltd | Real estate | 2026 |
| Jenkins Health Care Limited | Health & social care | 2009 |
| Jenkinsons Brickwork & Building Limited | Construction | 2023 |
| Jenner Estates Limited | Real estate | 2021 |
| Jensem Tech Ltd | Professional & scientific | 2022 |
| Jenvey Asset Management Ltd | Real estate | 2026 |
| Jerki Ltd | Hospitality | 2025 |
| Jermin Productions Ltd | Arts & recreation | 2013 |
| JET Aeronautics Repair & Test Solutions Ltd | Professional & scientific | 2024 |
| Jet.Loc. Limited | Real estate | 2013 |
| Jewell Lake Limited | Hospitality | 2025 |
| Jfak Investments Ltd | Real estate | 2024 |
| JFC Performance Ltd | Wholesale & retail | 2025 |
| JFR Building & Bespoke Refurbishment Ltd | Construction | 2024 |
| Jfrw Holding Ltd | Financial services | 2023 |
| Jfurreed Holdings Ltd | Professional & scientific | 2025 |
| JG Garage Doors Ltd | Manufacturing | 2019 |
| JG HR Solutions Limited | Administrative & support | 2016 |
| JG Resources Limited | Information & communication | 2016 |
| JGM & Associates Limited | Professional & scientific | 2006 |
| JH & LS Property Co. Ltd | Households | 2022 |
| JH Memorials Limited | Manufacturing | 2026 |
| Jhaw Ltd | Wholesale & retail | 2023 |
| JHG Developments Limited | Professional & scientific | 2009 |
| Jhona.Pesario Limited | Public administration | 2023 |
| JHW Business Solutions Limited | Professional & scientific | 2016 |
| JI Sheng Limited | Hospitality | 2026 |
| Jibu Solutions Ltd | Professional & scientific | 2019 |
| JIE Cheng Trading Limited | Hospitality | 2022 |
| Jigsaw Creative Solutions Limited | Wholesale & retail | 2012 |
| Jigsaw Health and Wellness Limited | Health & social care | 2016 |
| Jigsaw Project Solutions Limited | Professional & scientific | 2011 |
| Jijiki Limited | Information & communication | 2018 |
| Jimmyjack Services Limited | Construction | 2010 |
| Jinx GAS Ltd | Construction | 2025 |
| Jinx Heating Limited | Extraterritorial | 2025 |
| JJ Car Sales Ltd | Wholesale & retail | 2019 |
| JJ Portfolio Limited | Real estate | 2024 |
| JJ Transport Consultancy Limited | Professional & scientific | 2021 |
| Jj-Rjm Ltd | Arts & recreation | 2024 |
| JJE Commercial Property Enterprises Ltd | Real estate | 2024 |
| JJE Group Holdings Ltd | Financial services | 2024 |
| JJE Property Enterprises Ltd | Real estate | 2018 |
| JJF Park Holdings Ltd | Real estate | 2022 |
| JJG GAS Services Ltd | Construction | 2023 |
| JJL Energy Services Ltd | Construction | 2024 |
| JJP Mobile Tyres Ltd | Manufacturing | 2023 |
| JJS Carpet & Upholstery Cleaning Ltd | Administrative & support | 2020 |
| JK Gardening Services Limited | Administrative & support | 2024 |
| JK Renovations and Developments Ltd | Construction | 2024 |
| Jk's the Monkey Tree Limited | Hospitality | 2020 |
| JK3 Properties Ltd | Real estate | 2025 |
| JKC Sewing Limited | Manufacturing | 2020 |
| JKC Solutions Ltd | Manufacturing | 2008 |
| JKH Properties Ltd | Real estate | 2016 |
| JL & JA Properties Ltd | Real estate | 2020 |
| JL Consulting (Swansea) Ltd | Professional & scientific | 2025 |
| JL Owens Hospitality Ltd | Hospitality | 2025 |
| Jl&Ra Properties (Swansea) Limited | Real estate | 2021 |
| JLA Disposal Limited | Water & waste | 2002 |
| JLA Recycling Limited | Water & waste | 2000 |
| JLB Properties Ltd | Real estate | 2016 |
| JLC7 Ltd | Wholesale & retail | 2023 |
| JLD Design Ltd | Professional & scientific | 2025 |
| JLD Engineering and Survey Ltd | Construction | 2025 |
| JLD Property Management Ltd | Real estate | 2021 |
| JLE Companies Limited | Construction | 2019 |
| JLG Electrical Limited | Energy | 2017 |
| JLM Financial Services Limited | Financial services | 2010 |
| JLR Construction & Engineering Ltd | Construction | 2021 |
| JLR Residents Ltd | Real estate | 2026 |
| Jltc Solutions Ltd | Professional & scientific | 2020 |
| JLW Services Limited | Administrative & support | 2018 |
| JLW Tiling Ltd | Construction | 2024 |
| JM Building Contractors (Swansea) Limited | Construction | 2017 |
| JM Ents Group UK Ltd | Financial services | 2024 |
| JM Finance & Consulting Limited | Professional & scientific | 2025 |
| JM Property (Swansea) Ltd | Real estate | 2025 |
| JMC Group South Wales Limited | Construction | 2021 |
| JMC Substation Services Limited | Manufacturing | 2016 |
| JME Property Services Ltd | Real estate | 2019 |
| JMG Plumbing & Heating Limited | Construction | 2018 |
| JMJ Trading Limited | Wholesale & retail | 2025 |
| Jmmt Holdings Limited | Financial services | 2022 |
| Jmorales Limited | Construction | 2025 |
| JMP Group Holdings Limited | Financial services | 2024 |
| JMR Property Investments Ltd | Real estate | 2023 |
| Jmrw Ltd | Administrative & support | 2025 |
| JMT Stays Ltd | Real estate | 2023 |
| JMT Waste Ltd | Water & waste | 2023 |
| JMT World Ltd | Households | 2024 |
| JMW Heating and Plumbing Limited | Construction | 2016 |