| Integrated Rail Fencing Ltd | Construction | 2021 |
| International Car Wash Ltd | Wholesale & retail | 2026 |
| Ireoluwatomiwa Ltd | Health & social care | 2016 |
| Iscs Services Limited | Mining & quarrying | 2015 |
| J & EM Management Ltd | Arts & recreation | 2025 |
| J C Lewis Property Limited | Real estate | 2020 |
| J C Sims Limited | Information & communication | 2012 |
| J D Burford Limited | Manufacturing | 2005 |
| J Davies Travel Ltd | Transport & logistics | 2025 |
| J Evans Roofing Ltd | Construction | 2016 |
| J G Furlong Ltd | Construction | 2012 |
| J J Pritchard & Sons Ltd | Construction | 2024 |
| J K Forest Ltd | Hospitality | 2025 |
| J T Worlock Vehicle Repairs and Transport Services Ltd | Wholesale & retail | 2023 |
| J&J Welding & Fabrication Limited | Manufacturing | 2011 |
| J.E Commercial Maintenance and Tyres Ltd | Wholesale & retail | 2026 |
| J3MS Consulting Ltd | Professional & scientific | 2019 |
| Jabeen Distribution Ltd | Wholesale & retail | 2025 |
| Jacs (Aberdare) Limited | Hospitality | 2017 |
| JAE Performance Limited | Wholesale & retail | 2019 |
| James Woodington Ltd | Professional & scientific | 2014 |
| Jameswell Ltd | Education | 2004 |
| Jamie Pugh Dental Healthcare Limited | Health & social care | 2009 |
| Jarv's Plant Limited | Administrative & support | 2016 |
| Jason Heath Consulting Ltd | Education | 2022 |
| Jaspa Developments Limited | Financial services | 2019 |
| Jaspago Ltd | Financial services | 2025 |
| Jaybee Bars Ltd | Hospitality | 2025 |
| Jaytwinb Empire Limited | Wholesale & retail | 2025 |
| JCE Maintenance Ltd | Construction | 2022 |
| JCT Property Development Limited | Construction | 2005 |
| JDM Contractors Ltd | Construction | 2014 |
| JDR Steel Forge Limited | Arts & recreation | 2025 |
| JE Building & Sons Ltd | Administrative & support | 2024 |
| Jenney Creative Ltd | Professional & scientific | 2013 |
| JET ROD (SW) Ltd | Water & waste | 2021 |
| Jing Property Rental Ltd | Real estate | 2019 |
| JLW Commercials Ltd | Wholesale & retail | 2019 |
| JM Computers Europe Ltd | Information & communication | 2026 |
| JO YUM Limited | Hospitality | 2022 |
| John Adams Music Ltd | Wholesale & retail | 2018 |
| John Adams Recordings Ltd | Information & communication | 2023 |
| John Henry Gardiner Management Services Limited | Professional & scientific | 2014 |
| Joio Resources Ltd | Education | 2021 |
| JON Andrews Carpentry Ltd | Construction | 2017 |
| Jonrose Ltd | Construction | 2007 |
| Jordan Davies Rail Limited | Construction | 2018 |
| Jordan Pryor Carpentry Ltd | Construction | 2024 |
| Jordan Pryor Property Ltd | Real estate | 2025 |
| Josephine Anne Craig Ltd | Extraterritorial | 2023 |
| Josephine Anne Prangley Ltd | Extraterritorial | 2023 |
| Jpce Limited | Professional & scientific | 2013 |
| JPE Homes Limited | Construction | 2009 |
| JRD Engineering Services Ltd | Professional & scientific | 2020 |
| JT Labour Ltd | Administrative & support | 2025 |
| K & H Groundworks Limited | Construction | 1998 |
| K & S Chappell Properties Limited | Real estate | 2026 |
| K C Thomas Services Ltd | Other services | 2012 |
| K Munro ISW Ltd | Health & social care | 2024 |
| K.A.M Gough Limited | Health & social care | 2020 |
| K.E Facial Aesthetics Ltd | Health & social care | 2016 |
| KAD Design Projects Limited | Construction | 2007 |
| KAD Investment Group Ltd | Real estate | 2022 |
| Kaler Electrical Ltd | Construction | 2024 |
| Kamczat Transport UK Ltd | Transport & logistics | 2019 |
| Karahan Ltd | Hospitality | 2025 |
| Karaway Windows & Doors Ltd | Construction | 2022 |
| Kathryn Davies Physiotherapy Ltd | Health & social care | 2022 |
| Kdown Ltd | Wholesale & retail | 2025 |
| Keanelight Ltd | Other services | 2019 |
| Keepings Property Holdings Ltd | Real estate | 2024 |
| Kelray Properties Limited | Construction | 2019 |
| Kensington Harper Management System Ltd | Professional & scientific | 2015 |
| Kieron Gough Limited | Health & social care | 2012 |
| Kingdom of Chaos Ltd | Arts & recreation | 2019 |
| Kiroo Consulting Ltd | Information & communication | 2012 |
| Kixstop Ltd | Wholesale & retail | 2023 |
| KK Meredith Group Ltd | Wholesale & retail | 2026 |
| Krismac Groundworks Ltd | Construction | 2018 |
| KTA a Ltd | Real estate | 2025 |
| L and D J Williams Limited | Real estate | 2018 |
| L J Evans Carpentry & Building Ltd | Construction | 2022 |
| L Lewis Engineering Services Ltd | Real estate | 2014 |
| L&I Property Holdings Ltd | Real estate | 2025 |
| Langland Bay Estates Ltd | Real estate | 2021 |
| Langland Residential Ltd | Real estate | 2026 |
| Langley Fabrication & Welding Solutions Limited | Manufacturing | 2020 |
| LAU Construction Solutions Ltd | Construction | 2026 |
| LAU Property Solutions Ltd | Real estate | 2026 |
| LC Collins Properties Limited | Real estate | 2026 |
| LCC Properties & Development Ltd | Real estate | 2024 |
| Lccwales Limited | Water & waste | 2006 |
| LD Infratech Ltd | Professional & scientific | 2026 |
| Leanne & Lindsay Holdings Limited | Households | 2025 |
| Leegee Properties Ltd | Real estate | 2019 |
| Leonard Electrical Ltd | Manufacturing | 2016 |
| LET There BE Light Electrical Services Ltd | Construction | 2025 |
| Let’S Talk Mens Mental Health CIC | Wholesale & retail | 2020 |
| Levrg Automations Ltd | Information & communication | 2026 |
| Lewis Bros. Limited | Wholesale & retail | 1998 |