| J W AIM Ltd. | Professional & scientific | 2023 |
| J Williams Plumbing and Heating Limited | Construction | 2019 |
| J&A Building & Landscaping Ltd | Construction | 2024 |
| J.A.Lewis Ltd | Professional & scientific | 2023 |
| J9 Transport Services Ltd | Transport & logistics | 2025 |
| Jakjam Limited | Manufacturing | 2012 |
| Jamie Roberts Builders Ltd | Construction | 2025 |
| Janemac Ltd | Wholesale & retail | 2018 |
| JB Locum Limited | Other services | 2015 |
| JB Platform Hire Ltd | Other services | 2014 |
| JB Smiles Ltd | Other services | 2020 |
| Jeca JC Ltd | Hospitality | 2025 |
| Jessie's Place Limited | Administrative & support | 2017 |
| JG Retailing Ltd | Other services | 2011 |
| JJ Offshore Construction Ltd | Construction | 2015 |
| JKS Groundworks Limited | Construction | 2014 |
| JM Legowska Services Ltd | Other services | 2011 |
| JMR Cleaning Limited | Administrative & support | 2015 |
| John Evans Carpentry + Joinery Ltd | Other services | 2018 |
| John Owens Building, Joinery & Property Maintenance Limited | Construction | 2023 |
| Jones & Carter Limited | Construction | 1972 |
| Jordan & SON Ltd | Hospitality | 2006 |
| Joseph & William Joinery Co Ltd | Construction | 2025 |
| Joshua Tree Property Investment Group Limited | Real estate | 2020 |
| JPC Lifting Services Ltd | Construction | 2012 |
| JR Wind Services Limited | Professional & scientific | 2013 |
| JRB (Dairy) Consulting Ltd | Professional & scientific | 2018 |
| JRW NW Services Ltd | Administrative & support | 2017 |
| JS Carpentry and Joinery Ltd | Construction | 2024 |
| JTM Quality Used Cars Ltd | Other services | 2020 |
| Jupiter Offshore Wind Safety Services Ltd | Professional & scientific | 2019 |
| Just Imagine Interiors Ltd | Professional & scientific | 2019 |
| JWC Mind Ltd | Professional & scientific | 2023 |
| K N Hair Ltd | Other services | 2013 |
| K R Ellis Asset Management Ltd | Extraterritorial | 2018 |
| K&C Construction Limited | Construction | 1999 |
| K&K Software Ltd | Information & communication | 2024 |
| K.M. Construction (North Wales) Limited | Construction | 1982 |
| K.M. Plant Hire Limited | Extraterritorial | 1983 |
| K9 Self-Wash Systems Limited | Construction | 2026 |
| KAI Aaron Deliveries Ltd | Other services | 2021 |
| Kairos Biotech Ltd | Professional & scientific | 2019 |
| Kapital Properties Ltd | Real estate | 2026 |
| Kavicks Limited | Wholesale & retail | 1976 |
| KAY Investment Holdings Ltd | Financial services | 2020 |
| Keegan Asset Management Ltd | Professional & scientific | 2023 |
| Kelly & Owen Plumbing & Heating Limited | Construction | 2010 |
| Ken's Fish & Chips Limited | Hospitality | 2023 |
| Kendley Services Limited | Real estate | 2012 |
| KH & DEL UK Ltd | Wholesale & retail | 2023 |
| KHS Climate Ltd | Professional & scientific | 2020 |
| KHS Electrical (NW) Ltd | Construction | 2020 |
| KHS Group Ltd | Construction | 2016 |
| KHS Renewables Ltd | Professional & scientific | 2020 |
| Kilo Software Ltd | Information & communication | 2022 |
| Kinsey Holdings Limited | Extraterritorial | 2022 |
| Kitchens of Abergele Ltd | Wholesale & retail | 2015 |
| KM Environmental Limited | Water & waste | 2003 |
| Korwyn Developments Limited | Construction | 2019 |
| KR Financial Consulting Ltd | Other services | 2015 |
| KRM Construction Ltd | Administrative & support | 2016 |
| Kyren Wilson Snooker Ltd | Arts & recreation | 2017 |
| L & E Healthcare Limited | Wholesale & retail | 2021 |
| L B Logs and Kindling Ltd | Wholesale & retail | 2025 |
| L J Brookes Ltd | Construction | 2023 |
| L'S Coffee and Book Shop Limited | Hospitality | 2014 |
| LAJ Property NW Limited | Real estate | 2025 |
| Lakeview Solutions Ltd | Other services | 2018 |
| Langbury Limited | Arts & recreation | 2010 |
| Larkin Auto Electrical Limited | Professional & scientific | 2008 |
| Laser Micromachining Limited | Professional & scientific | 2004 |
| Lavenders (NW) Ltd | Other services | 2014 |
| LBI Design Limited | Professional & scientific | 2022 |
| Lbnh Property Holdings Ltd | Real estate | 2026 |
| LD Tiling (NW) Ltd | Other services | 2018 |
| LEE Tattum Roofing Services Ltd | Other services | 2014 |
| Leewyn Properties Limited | Real estate | 2017 |
| Legal Cafe Ltd | Education | 2020 |
| Lenka LUL Ltd | Other services | 2020 |
| LET the Sunshine in BI Folds Ltd | Manufacturing | 2021 |
| Leung Food Supplies Ltd. | Wholesale & retail | 2004 |
| Leviathan Pits Limited | Manufacturing | 2023 |
| LGR Engineering Ltd | Professional & scientific | 2022 |
| Lhra Consultancy Limited | Professional & scientific | 2014 |
| Liba and Skye Ltd | Wholesale & retail | 2024 |
| Lightbown Environmental Limited | Water & waste | 2012 |
| Limit Point Vision Limited | Education | 2010 |
| Lion Safety Consultants Ltd | Professional & scientific | 2025 |
| Liprovit UK Ltd | Manufacturing | 2018 |
| Lite Linke Limited | Manufacturing | 2017 |
| Little Blessings Ltd | Health & social care | 2024 |
| Little Explorers Preshool Limited | Administrative & support | 2016 |
| Little Haven Retreat Limited | Hospitality | 2017 |
| Livingstone Electrical Ltd | Construction | 2024 |
| LJ Evans Window Cleaning Services Ltd | Administrative & support | 2015 |
| LJB Properties One Ltd | Real estate | 2025 |
| LJG Properties Limited | Real estate | 2018 |
| LKJ Aesthetics Ltd | Health & social care | 2023 |
| Llandudno Holidays Ltd | Other services | 2018 |
| Llandudno Junction Developments Limited | Construction | 2023 |