| J&L Stays Ltd | Real estate | 2025 |
| J&M Beauty Group Ltd | Wholesale & retail | 2024 |
| J-Wharf Residential Limited | Professional & scientific | 2004 |
| J. C. Securities Limited | Construction | 2003 |
| J. Lacey Ltd | Construction | 2014 |
| J.A.D. Properties South Wales Ltd | Real estate | 2018 |
| J.A.H (Construction) Limited | Construction | 1994 |
| J.B.Boobyer Construction Ltd | Construction | 2020 |
| J.C.W. (Loft Conversions) Limited | Construction | 1981 |
| J.R. Fabrication and Welding Ltd | Manufacturing | 2022 |
| JAC Rocks Ltd | Health & social care | 2019 |
| Jack & Rose Limited | Manufacturing | 2021 |
| Jackson Cabs Ltd. | Transport & logistics | 2018 |
| Jaco Limited | Real estate | 2025 |
| Jade Kitchen Limited | Hospitality | 2021 |
| Jadefell Limited | Extraterritorial | 2026 |
| Jadeover Limited | Extraterritorial | 2025 |
| Jaegel Ltd | Construction | 2018 |
| JAH Traffic Limited | Administrative & support | 2017 |
| JAI SD Properties Ltd | Real estate | 2025 |
| JAI Store Ltd | Wholesale & retail | 2019 |
| James Canton Property Development Limited | Construction | 2015 |
| James H Kinsey (2010) Limited | Wholesale & retail | 2010 |
| James Installation & Maintenance Ltd | Construction | 2009 |
| James Perry Developments Ltd | Construction | 2021 |
| Jamjay Ltd | Information & communication | 2022 |
| JAN B Engineering Limited | Professional & scientific | 2017 |
| Janex Developments Ltd | Construction | 2026 |
| Jareco Ltd | Professional & scientific | 2020 |
| Jarley Limited | Health & social care | 2023 |
| JAS Developments Limited | Construction | 2002 |
| Jasgal Limited | Public administration | 2023 |
| Jason Lucas Operations Ltd | Arts & recreation | 2022 |
| Jasongreenproperty Ltd | Real estate | 2021 |
| Jawda Arabia Ltd | Construction | 2025 |
| JAY J Davies Limited | Construction | 2005 |
| JAY Retail Hub Ltd | Wholesale & retail | 2025 |
| Jaycubed Creative Ltd. | Professional & scientific | 2015 |
| Jaydean Development & Construction Limited | Real estate | 2006 |
| Jaydean Properties Limited | Real estate | 2008 |
| Jayhale Limited | Wholesale & retail | 2024 |
| Jaymaster Limited | Extraterritorial | 2025 |
| Jazzamoon Limited | Professional & scientific | 2019 |
| JB Safety and Engineering Limited | Professional & scientific | 2015 |
| JBS 95 Bidco Limited | Financial services | 2024 |
| JBS 95 Midco 1 Limited | Financial services | 2024 |
| JBS 95 Midco 2 Limited | Financial services | 2024 |
| JBS 95 Topco Limited | Financial services | 2024 |
| JC Recoveries Limited | Administrative & support | 2017 |
| JCD Engineering Services Limited | Professional & scientific | 2015 |
| JCD Facade Services Ltd | Other services | 2016 |
| JCS Group Holdings Ltd | Financial services | 2025 |
| JDM Roofing & Carpentry Ltd | Construction | 2021 |
| JDP (Holdings) Limited | Wholesale & retail | 2015 |
| Jdvm Property Maintenance Limited | Construction | 2015 |
| JE Autotech Ltd | Wholesale & retail | 2026 |
| Jedw Consulting Ltd | Professional & scientific | 2023 |
| Jeff Tombs Porthcawl Landscapes Limited | Administrative & support | 2005 |
| Jehu (Land Holdings) Limited | Construction | 2022 |
| Jehu (Langstone) Limited | Construction | 2011 |
| Jehu Energy Solutions Limited | Construction | 2011 |
| Jeit Support Ltd | Information & communication | 2019 |
| Jenesis Limited | Real estate | 2021 |
| Jenkins Builders Limited | Construction | 2019 |
| Jenkins Engineering Solutions Limited | Construction | 2018 |
| Jenkins Garages (Southerndown) Limited | Wholesale & retail | 1958 |
| Jenkinsco Mechanics Ltd | Wholesale & retail | 2026 |
| Jeremy Davies Limited | Manufacturing | 2005 |
| Jeris Music Ltd | Arts & recreation | 2024 |
| Jesscompany Ltd | Transport & logistics | 2022 |
| JET Catering Ltd | Wholesale & retail | 2024 |
| JET Electrical and Network Solutions Ltd | Construction | 2025 |
| Jewell Contractors Ltd | Construction | 2011 |
| JGA Homes Ltd | Real estate | 2016 |
| JH Education International Limited | Education | 2017 |
| JHB Business Services Ltd | Professional & scientific | 2016 |
| Jhei Services Limited | Professional & scientific | 2023 |
| Jinx Sport Ltd | Real estate | 2010 |
| Jinx Sports Media Ltd | Information & communication | 2007 |
| JJ Data Ltd | Information & communication | 2026 |
| JJ Electrical Group Ltd | Construction | 2025 |
| Jjog Holdings & Investments Limited | Wholesale & retail | 2020 |
| JJW Carpentry Limited | Construction | 2019 |
| JK Thermal Insulation Services Limited | Construction | 2016 |
| JL Precision Ltd | Manufacturing | 2022 |
| JL Trades Limited | Information & communication | 2026 |
| JLD Engineering and Construction Ltd | Construction | 2025 |
| Jltp Golf Limited | Arts & recreation | 2017 |
| JM Business Improvement Limited | Professional & scientific | 2018 |
| JM Holdings and Investments Ltd | Financial services | 2019 |
| JM Print Ltd | Manufacturing | 2023 |
| JMD Cleaning Services Ltd | Administrative & support | 2019 |
| JME Design Limited | Professional & scientific | 2017 |
| JMJ Electrical Limited | Construction | 2019 |
| JMO Civils & Groundworks Ltd | Construction | 2025 |
| Joanne Lewis Accountancy Limited | Professional & scientific | 2018 |
| Jobs-On Recruitment Ltd | Hospitality | 2025 |
| JOD Properties Ltd | Real estate | 2020 |
| Jod.T Business Limited | Administrative & support | 2023 |
| John Raymond Transport Limited | Transport & logistics | 1945 |