| JBM Mortgage Brokers Ltd | Financial services | 2015 |
| JBM Mortgages Limited | Financial services | 2005 |
| JC Resin Ltd | Construction | 2023 |
| JDH Bars Ltd | Hospitality | 2018 |
| Jean Ramble CYF | Real estate | 2024 |
| Jellzi Ltd | Construction | 2025 |
| Jenkins Plumbing Limited | Construction | 2026 |
| Jenko Holdings Limited | Financial services | 2026 |
| Jennifer Melly Holdings Limited | Financial services | 2025 |
| Jennifer Melly Law Limited | Professional & scientific | 2014 |
| Jennifer Melly Properties Ltd | Real estate | 2025 |
| JET Experts Ltd | Wholesale & retail | 2022 |
| Jewel & Grace Ltd | Manufacturing | 2023 |
| JGR Educate LLP | | 2016 |
| JGS Plumbing Services Ltd | Construction | 2026 |
| Jjebj Ltd | Real estate | 2021 |
| JJO Management Services Limited | Manufacturing | 2023 |
| JLM Roofing Solutions Ltd | Construction | 2024 |
| JLP Detailing Ltd | Administrative & support | 2022 |
| JMM04 Ltd | Transport & logistics | 2025 |
| JMS GAS Limited | Construction | 2025 |
| JN Care Solutions Limited | Health & social care | 2024 |
| JNJ Vintage Clothing Limited | Wholesale & retail | 2026 |
| Joes Doors Ltd | Manufacturing | 2020 |
| Joes Sliding Wardrobes Ltd | Construction | 2023 |
| John Pearce (Glynneath) Holdings Limited | Hospitality | 2013 |
| John Pembs Motors Ltd | Wholesale & retail | 2021 |
| John Smith Holdings Limited | Financial services | 2025 |
| Joio CYF | Information & communication | 2012 |
| Jolly Jackpot Ltd | Wholesale & retail | 2025 |
| Jones and Jones Renewables Ltd | Energy | 2013 |
| Jones Hamilton Associates Ltd | Wholesale & retail | 2014 |
| Jordan & Sons Farm Ltd | Agriculture & fishing | 2022 |
| JOSAN19 Ltd | Wholesale & retail | 2023 |
| Joseph Lewis Design Limited | Professional & scientific | 2023 |
| Jpig Hospitality Limited | Hospitality | 2025 |
| JR Bodyworx Limited | Wholesale & retail | 2018 |
| JR Mortgage House Limited | Financial services | 2022 |
| JS Trading (Universal) Ltd | Wholesale & retail | 2025 |
| JSP Properties ( Wales ) Ltd | Administrative & support | 2018 |
| JT Custom Metalworks Ltd | Professional & scientific | 2021 |
| JT SUB Limited | Hospitality | 2006 |
| Jtekt Automotive UK Limited | Manufacturing | 1997 |
| JUD Building & Maintenance Limited | Construction | 2013 |
| Just Meacs Consulting Ltd | Professional & scientific | 2026 |
| Justin Bailey Ltd | Construction | 2019 |
| JW Industrial Ltd | Administrative & support | 2025 |
| JW Parfitt & Sons Limited | Administrative & support | 2012 |
| K & J Property Solutions Ltd | Construction | 2025 |
| K & Q Hair Ltd | Other services | 2021 |
| K Thomas Waste/Recycling Limited | Water & waste | 2014 |
| K&D Europe Constructions Ltd | Construction | 2023 |
| K&K Timber Frame Ltd | Manufacturing | 2019 |
| K&M Building Solutions Ltd | Construction | 2020 |
| K8M PMU Ltd | Other services | 2025 |
| KAD Construct (UK) Ltd | Construction | 2013 |
| KAJ Electricals Ltd | Construction | 2025 |
| KAP Carpentry Ltd | Construction | 2024 |
| Karishna Ltd | Real estate | 2025 |
| Katalyst Group Ltd | Professional & scientific | 2024 |
| Kate's Unisex Salon Ltd | Other services | 2018 |
| Katta Homes Private Limited | Manufacturing | 2024 |
| Kaur Invest Ltd | Real estate | 2026 |
| KCJ Cleaning & Facilities Management Ltd | Administrative & support | 2024 |
| KCM Plumbing and Heating Ltd | Construction | 2020 |
| Keen Investments Limited | Extraterritorial | 2012 |
| Keep Getting Better Fitness Ltd | Arts & recreation | 2024 |
| Keinwyn Vickress Ltd | Transport & logistics | 2018 |
| Keizon's Care Ltd | Public administration | 2024 |
| Kemeh Limited | Wholesale & retail | 2019 |
| Kemeh Properties Limited | Real estate | 2024 |
| Kenzo Autos Ltd | Wholesale & retail | 2025 |
| Ketocrate Ltd | Manufacturing | 2025 |
| Keypro Auto Locksmith Ltd | Wholesale & retail | 2026 |
| KFM Motorhaus Limited | Wholesale & retail | 2025 |
| KH Unmanned Ltd | Manufacturing | 2019 |
| Khadijah & Co. Art Curation Ltd | Wholesale & retail | 2025 |
| Kimberley Hydro Limited | Energy | 2010 |
| Kirk Phillips Consulting Ltd | Information & communication | 2026 |
| KJB Cleaning Services Wales Ltd | Administrative & support | 2019 |
| KJE Solutions Limited | Manufacturing | 2023 |
| KJR Training Ltd | Education | 2011 |
| KM Security & K9 Specialist Ltd | Administrative & support | 2018 |
| KMH Land & Property Ltd | Real estate | 2023 |
| Knott's MOT Centre Ltd | Wholesale & retail | 2012 |
| Kobi Gecko Limited | Wholesale & retail | 2020 |
| Komar Trading Ltd | Wholesale & retail | 2022 |
| KP Wealth Ltd | Financial services | 2021 |
| KPS Global Services Limited | Information & communication | 2010 |
| Kraken Clean Ltd | Administrative & support | 2024 |
| Krish Rentals Limited | Real estate | 2025 |
| KRP Carpentry & Building Ltd | Construction | 2022 |
| KRP Renovations Ltd | Construction | 2023 |
| KS Retail Ltd | Wholesale & retail | 2018 |
| Kumar Abbey Fishbar Ltd | Hospitality | 2021 |
| L & H Leisure Limited | Hospitality | 2019 |
| L F Williams Limited | Financial services | 2012 |
| L Phillips Properties Ltd | Real estate | 2023 |
| L&Gk Properties Limited | Real estate | 2025 |
| L.B.F Laboratory Ltd | Health & social care | 2022 |