| Ingles Digital Creations Limited | Professional & scientific | 2025 |
| Ingram Plant Services Ltd | Manufacturing | 2021 |
| Insulationize Ltd | Construction | 2025 |
| IP Site Fabrications Limited | Manufacturing | 2018 |
| IP Site Solutions UK Limited | Manufacturing | 2010 |
| Ivyh Ltd | Other services | 2024 |
| J & B Utilities Limited | Construction | 2023 |
| J.L Evans Properties Ltd | Households | 2022 |
| Jaer Property Development Ltd | Real estate | 2021 |
| Java 2 Limited | Real estate | 2024 |
| Jaxon Electrical Services Limited | Construction | 2019 |
| JB Building & Maintenance Limited | Construction | 2021 |
| JCP Construction & Maintenance Ltd | Construction | 2018 |
| Jeff's Garage & MOT Centre Ltd | Wholesale & retail | 2026 |
| JF Plumbing & Bathrooms Ltd | Construction | 2024 |
| JF Plumbing & Heating (South Wales) Ltd | Construction | 2024 |
| JFD Carpentry Limited | Manufacturing | 2025 |
| JGP Motors Ltd | Wholesale & retail | 2025 |
| JJM Aviation Consulting Ltd | Professional & scientific | 2026 |
| JJN Properties Ltd | Real estate | 2024 |
| JK Iconic Cars Ltd | Wholesale & retail | 2026 |
| JL Civils & Groundworks Ltd | Construction | 2022 |
| JLG Fitness Limited | Wholesale & retail | 2019 |
| JM Express Freight Limited | Transport & logistics | 2019 |
| JM Landscaping Limited | Administrative & support | 2025 |
| JM Rental Properties Ltd | Households | 2025 |
| Joan Collins Beauty Limited | Extraterritorial | 2012 |
| Jones Contractors Ltd | Construction | 2025 |
| Jordan S Welding Ltd | Manufacturing | 2024 |
| JR Properties Limited | Real estate | 2014 |
| JRS - Tiling Limited | Construction | 2024 |
| JS Plant Limited | Construction | 2023 |
| JTC Bookkeeping Limited | Professional & scientific | 2011 |
| JTS Flooring Ltd | Construction | 2025 |
| Julie Dale Limited | Health & social care | 2018 |
| Just Air Holdings Ltd | Financial services | 2020 |
| K & M Traditional Meats Limited | Hospitality | 2014 |
| K Dunkerton Utilities Limited | Construction | 2023 |
| K L Groundworks Limited | Construction | 2014 |
| K Tiling Contractors Ltd | Construction | 2026 |
| K.J. Services Holdings Limited | Financial services | 2021 |
| Kansas Bidco Limited | Professional & scientific | 2020 |
| Kansas Midco Limited | Professional & scientific | 2020 |
| Kansas Topco Limited | Professional & scientific | 2020 |
| Kebabcraft Ltd | Hospitality | 2025 |
| Keymech Designs Ltd | Professional & scientific | 2026 |
| KG Building & Roofing Ltd | Construction | 2026 |
| Kimberlane Limited | Extraterritorial | 1979 |
| KJ Forecourts Limited | Wholesale & retail | 2022 |
| Kjlake Ventures Ltd | Wholesale & retail | 2023 |
| KJS Vehicle Solutions Ltd | Wholesale & retail | 2021 |
| KP Steel Craft Ltd | Manufacturing | 2017 |
| Krefts&Co Limited | Wholesale & retail | 2025 |
| KTB Carpets and Beds Limited | Wholesale & retail | 2024 |
| L J Z Lettings Ltd | Real estate | 2024 |
| L Watkins Electrical Ltd | Construction | 2023 |
| L&A Garden Rooms Ltd | Construction | 2025 |
| L&C Home Renovations Limited | Construction | 2024 |
| Lach Edibles and African Stores Ltd | Wholesale & retail | 2026 |
| Laird HFD Ltd | Information & communication | 2025 |
| Lake Properties Ltd | Households | 2025 |
| Larchfield Grange Limited | Hospitality | 2021 |
| LBP Property Developments Ltd | Construction | 2022 |
| Leadstones Digital Limited | Information & communication | 2026 |
| Leaping Deer Forest School and Wilderness Skills Limited | Administrative & support | 2016 |
| Leisure Home Products Ltd | Wholesale & retail | 2020 |
| Leonhard Lang (UK) Ltd | Administrative & support | 2002 |
| Lerwill Ltd | Wholesale & retail | 2024 |
| Let’S Go to Play Ltd | Arts & recreation | 2023 |
| Lewis Performance Tuning Ltd | Wholesale & retail | 2025 |
| Liam Davies Snooker Limited | Arts & recreation | 2024 |
| Lift-Equip South Wales Ltd | Manufacturing | 2026 |
| Light Transport Solutions Ltd | Transport & logistics | 2024 |
| LKA Property Ltd | Real estate | 2025 |
| LLT Limited | Hospitality | 2014 |
| LMC Tiles Limited | Wholesale & retail | 2020 |
| Locum Clinical Services Limited | Health & social care | 2018 |
| Loom and Luster Ltd | Manufacturing | 2025 |
| Louvain Lettings Ltd | Real estate | 2021 |
| Louvain Properties Ltd | Construction | 2013 |
| Lozana Organics Limited | Manufacturing | 2024 |
| LQK Engineering Limited | Professional & scientific | 2024 |
| LTH Automotive Limited | Manufacturing | 2020 |
| Luma Investments Ltd | Real estate | 2025 |
| M & J (Europe) Limited | Manufacturing | 1990 |
| M & J Consultancy and Management Limited | Real estate | 2016 |
| M & J Slack Limited | Real estate | 2025 |
| M R Property Management Ltd | Households | 2021 |
| M&J Commercial Property Ltd | Real estate | 2023 |
| M.R Civils Ltd | Construction | 2025 |
| Made in Tredegar Ltd | Arts & recreation | 2012 |
| Madola Energy Ltd | Construction | 2013 |
| Madola Merch Ltd | Extraterritorial | 2020 |
| Marleys Munchies Ltd | Hospitality | 2022 |
| Martindale Technical Services Ltd | Information & communication | 2014 |
| MAX Logistics Limited | Transport & logistics | 2011 |
| Maxburn Limited | Construction | 2021 |
| MBD 213 Limited | Professional & scientific | 2024 |
| MCE Property Group Limited | Real estate | 2024 |
| Mcilhiney Ltd | Real estate | 2024 |