| Industrial Training UN Limited | Education | 2024 |
| Infinity & Beyond Properties Limited | Administrative & support | 2018 |
| Ingleside Engineering Limited | Professional & scientific | 2000 |
| Iniquity the Movie Ltd | Arts & recreation | 2025 |
| Inspire Facilities UK Ltd | Construction | 2024 |
| Inteldynamics Limited | Manufacturing | 2016 |
| Intuety Ltd | Information & communication | 2020 |
| Ioan Heycock Services Limited | Construction | 2022 |
| Ionut Builders Ltd | Construction | 2026 |
| Island Pride Property Management Limited | Hospitality | 2018 |
| Ivor Green Timber & Forestry Products Ltd | Manufacturing | 2017 |
| Ivor Protheroe Ltd | Transport & logistics | 2016 |
| Ixus Distribution Limited | Professional & scientific | 2014 |
| Ixus Electrical Solutions Limited | Construction | 2026 |
| Ixus Group Limited | Professional & scientific | 2020 |
| Ixus Hvac Solutions Limited | Professional & scientific | 2024 |
| J & a Consultants (Neath) Limited | Health & social care | 2023 |
| J & C Shearer Properties Limited | Real estate | 2015 |
| J D Marine & Sons Limited | Construction | 2012 |
| J Fernando Ltd | Real estate | 2019 |
| J I Asset Management Ltd | Financial services | 2018 |
| J&L Barron Properties Ltd | Real estate | 2023 |
| J&L Trading Limited | Wholesale & retail | 2020 |
| J.E.S. (Port Talbot) Limited | Other services | 1987 |
| J.E.S. Group Limited | Manufacturing | 2015 |
| J.E.S. Holdings Limited | Other services | 2016 |
| J.R.J Mechanical Ltd | Wholesale & retail | 2023 |
| J.V.R Real Estates Ltd | Real estate | 2021 |
| J.V.R Stores Ltd | Wholesale & retail | 2016 |
| J43 Storage Limited | Extraterritorial | 2014 |
| JA11 Consulting Limited | Administrative & support | 2016 |
| Jack Davies Contracting Limited | Agriculture & fishing | 2025 |
| Jade Garden Chinese Limited | Hospitality | 2014 |
| Jaipur Porthcawl Ltd | Hospitality | 2011 |
| Jakilau Ltd | Health & social care | 2023 |
| James & Jones Investments Ltd | Real estate | 2023 |
| James & Nicholas Architects Engineers Limited | Construction | 2024 |
| James & Nicholas Limited Liability Partnership | | 2002 |
| Jamie Jones Snooker Limited | Arts & recreation | 2013 |
| Janta Enterprises Ltd | Health & social care | 2025 |
| Jarvis Networks Ltd | Information & communication | 2014 |
| JB Events and Tickets Ltd | Wholesale & retail | 2024 |
| JB Fernando Ltd | Health & social care | 2021 |
| JBA Rentals & Holiday Lets Ltd | Real estate | 2025 |
| JCB Electrical Services Ltd | Construction | 2026 |
| JCM E-Commerce Ltd | Information & communication | 2019 |
| JD Group Services Limited | Manufacturing | 2017 |
| JD3 Ltd | Professional & scientific | 2026 |
| JDC Bar Ltd | Hospitality | 2022 |
| JDM Transfers Limited | Manufacturing | 2017 |
| Jennys DEN Limited | Wholesale & retail | 2021 |
| Jgme Holdings UK Limited | Professional & scientific | 2018 |
| JGS Insights Ltd | Professional & scientific | 2026 |
| JH Resin & Printed Concrete Ltd | Construction | 2024 |
| JH2 Ltd | Construction | 2026 |
| JHM Training & Consultancy Limited | Education | 2009 |
| JHS (Retail) Limited | Wholesale & retail | 2004 |
| Jimmys Bar [Port Talbot] Ltd | Arts & recreation | 2019 |
| JJ Heart Ltd | Health & social care | 2026 |
| Jjad Properties Ltd | Real estate | 2019 |
| JKM Properties Rentals Ltd | Real estate | 2025 |
| JL Engineering Ltd. | Manufacturing | 2025 |
| JLL Designs Ltd | Manufacturing | 2016 |
| JM Entertainment Limited | Arts & recreation | 2017 |
| JM Masa Limited | Financial services | 2024 |
| JM Prop Investments Ltd | Real estate | 2023 |
| JMB Asset Management Ltd | Real estate | 2013 |
| JNA Butchers Ltd | Wholesale & retail | 2025 |
| Joanne Padley Ltd | Administrative & support | 2020 |
| John Property Management Limited | Real estate | 2025 |
| Joint Venture Recruit Ltd | Administrative & support | 2014 |
| Jones & Sheehy Property Services Limited | Real estate | 2021 |
| Joyan Investments Limited | Real estate | 2020 |
| JPM Roofing & Building Ltd | Construction | 2025 |
| JS Distribution Ltd | Transport & logistics | 2023 |
| JSD Building Maintenance Limited | Construction | 2016 |
| JSD Timber Limited | Wholesale & retail | 2022 |
| Just Mot's Ltd | Wholesale & retail | 2018 |
| K & J Pipeline Supplies Limited | Wholesale & retail | 2011 |
| K & M Soper Limited | Wholesale & retail | 2006 |
| K & S Taxi Limited | Transport & logistics | 2024 |
| K and C Enterprises Ltd | Wholesale & retail | 2022 |
| K&V Elite Equine Products Ltd | Manufacturing | 2019 |
| K90 RAW & Hydro Ltd | Wholesale & retail | 2020 |
| KAI Barber Ltd | Other services | 2025 |
| KAL Loft Conversion Ltd | Construction | 2024 |
| Kani Barber Port Talbot Ltd | Other services | 2024 |
| Kani Barber Shop Limited | Other services | 2026 |
| Kapitrick Ltd | Real estate | 2022 |
| Kask Logistics Ltd | Transport & logistics | 2023 |
| Kasria UK Ltd | Wholesale & retail | 2026 |
| KAT Coin DU Monde Limited | Administrative & support | 2022 |
| Kaya Kara Ltd | Hospitality | 2025 |
| KCM Fitness Studio Ltd | Arts & recreation | 2022 |
| KD Steelwork Ltd | Construction | 2025 |
| Kenfig Self Storage Ltd | Transport & logistics | 2023 |
| Kennedy Burger Ltd | Hospitality | 2025 |
| Kerrigan Reinforcing Limited | Construction | 2015 |
| Kevin Alford Construction Ltd | Construction | 2024 |
| Key LETTINGS1 Limited | Real estate | 2012 |