| Johnsey Estates UK Limited | Construction | 1990 |
| Johnson Builds Ltd | Construction | 2025 |
| Jolliffe Pontypool Ltd | Transport & logistics | 2020 |
| Jones Tree Care South Wales Ltd | Administrative & support | 2025 |
| Jordan Group Limited | Real estate | 2024 |
| Josh Ramsey Construction Ltd | Construction | 2021 |
| JP Consultancy Group Ltd | Extraterritorial | 2024 |
| JP Data Ltd | Information & communication | 2026 |
| JR Kitchens Limited | Construction | 2019 |
| JRJ Creative Ltd | Professional & scientific | 2026 |
| JRW Utility Services Ltd | Construction | 2016 |
| JSM Heating Services Ltd | Construction | 2023 |
| JSP Building Contractors Ltd | Construction | 2021 |
| JT Landscapes Fencing & Tree Services Ltd | Administrative & support | 2026 |
| JTW Detailing & Valeting Ltd | Wholesale & retail | 2022 |
| Juri Investments Limited | Real estate | 2015 |
| K & a Valeting Ltd | Administrative & support | 2026 |
| K & G Blinds Ltd | Households | 2024 |
| K Wallace & Co Holdings Ltd | Financial services | 2025 |
| Kabokane K9 Services Ltd | Agriculture & fishing | 2025 |
| Kaktus Adventure Vans Limited | Manufacturing | 2017 |
| Karol Karolczyk Ltd | Transport & logistics | 2021 |
| Kate O'Neill Coaching Ltd | Administrative & support | 2021 |
| KB Build & Rendering Solutions Ltd | Construction | 2022 |
| KD System Services Ltd | Manufacturing | 2019 |
| Keepsake Balloons Ltd | Wholesale & retail | 2022 |
| Kenmore Stanton Ltd | Wholesale & retail | 2025 |
| Kenwood FOX Ltd | Wholesale & retail | 2025 |
| Kenzy Care Ventures Ltd | Other services | 2024 |
| Kerian Lets Limited | Real estate | 2024 |
| Keswick Jubilee Ltd | Wholesale & retail | 2025 |
| Keymill Limited | Hospitality | 2007 |
| KG Conveyancing Limited | Professional & scientific | 2026 |
| Kh&C Ltd | Financial services | 2020 |
| Kh&P Ltd | Financial services | 2019 |
| Kilnala College Ltd | Wholesale & retail | 2024 |
| Kinshard Properties Limited | Real estate | 2025 |
| Kipling Ninth Ltd | Wholesale & retail | 2025 |
| Kireto Ltd | Transport & logistics | 2017 |
| KIT DID IT Limited | Hospitality | 2024 |
| Kleener Property Ltd | Real estate | 2025 |
| KLT Cleaning Company CYF | Administrative & support | 2025 |
| Knightsvale Group Limited | Real estate | 2022 |
| Kodaq Ltd | Information & communication | 2026 |
| KOR Ltd | Wholesale & retail | 2024 |
| Kuchhadiya Oak Limited | Hospitality | 2021 |
| Kurd 2 (Ponty) Ltd | Other services | 2025 |
| Kymin Construction Limited | Construction | 1995 |
| L & S Electrics Limited | Construction | 2021 |
| L Brown 14 Sports Limited | Arts & recreation | 2019 |
| L Emanuel Carpentry Solutions Ltd | Other services | 2025 |
| L Kent Ltd | Administrative & support | 2019 |
| L W Sprinklers Limited | Construction | 2024 |
| L&J Developments Limited | Construction | 2017 |
| L.B. Adelphi Limited | Wholesale & retail | 1977 |
| L.P.P. Rail Ltd | Construction | 2017 |
| LA Cueva Ltd | Hospitality | 2025 |
| Labuda SP Ltd | Professional & scientific | 2025 |
| Landeco Ltd | Professional & scientific | 2024 |
| Landseer Crome Ltd | Wholesale & retail | 2025 |
| Landybay.Com Ltd | Wholesale & retail | 2024 |
| Lansdowne Beech Ltd | Wholesale & retail | 2025 |
| Larc Enterprise Ltd | Hospitality | 2009 |
| Latelow Henley Ltd | Wholesale & retail | 2025 |
| Lawns ARE US Ltd | Administrative & support | 2025 |
| LCK Fibre & Data Ltd | Manufacturing | 2026 |
| LDM Consulting Limited | Professional & scientific | 2023 |
| LEE Upholstery & Frames Limited | Manufacturing | 2008 |
| Leetsteel Ltd | Professional & scientific | 2018 |
| Legacy Gym 24 Limited | Arts & recreation | 2018 |
| Let’S Go Walkies With Sarah Ltd | Wholesale & retail | 2025 |
| Lewis Jackson Safety Ltd | Public administration | 2025 |
| Lewys & Morgan Coaching Ltd | Education | 2022 |
| Libertyview Limited | Real estate | 2015 |
| Liffey Rivers Ltd | Wholesale & retail | 2024 |
| Lift Fitness Limited | Health & social care | 2017 |
| Ligger Bay Limited | Real estate | 2012 |
| Lighthouse Merchants Ltd | Wholesale & retail | 2023 |
| Lime Kiln Estate Management Company Limited | Households | 2015 |
| Limefield Properties Limited | Construction | 2016 |
| Limitless Construction (MB) Limited | Construction | 2020 |
| Lincolndoverr Ltd | Wholesale & retail | 2025 |
| Lisbon Pitts Ltd | Wholesale & retail | 2025 |
| Lisbon Varner Ltd | Wholesale & retail | 2025 |
| Little Chums Day Nurseries Limited | Education | 2007 |
| Little Crown Inn Limited | Hospitality | 2022 |
| Little Rick Limited | Wholesale & retail | 2022 |
| Little Roots (Torfaen) Limited | Health & social care | 2025 |
| Little Stars Mamhilad Limited | Health & social care | 2025 |
| Little Stars Nursery Ebbw Fawr Ltd | Health & social care | 2025 |
| Little Stars Nursery LLP | | 2002 |
| Livayah's Ltd | Hospitality | 2026 |
| LJ Literature Ltd | Arts & recreation | 2019 |
| LJA Industrial Solutions Ltd | Manufacturing | 2014 |
| LK Lifting Services Ltd | Construction | 2025 |
| Llety Homes Ltd | Real estate | 2018 |
| LLF Ltd | Manufacturing | 2010 |
| Lloyds Lots Ltd | Wholesale & retail | 2022 |
| LMB Construction (SW) Limited | Construction | 2022 |
| Local Glazing Ltd | Construction | 2023 |