| Isla Roots Ltd | Administrative & support | 2026 |
| Isleham Business Park Ltd | Construction | 2021 |
| Itca Solutions Ltd | Information & communication | 2019 |
| Iverberry Investments Limited | Real estate | 2017 |
| IVY and Stone Ltd | Administrative & support | 2020 |
| Ivyleaf Limited | Households | 2003 |
| Ixya UK Limited | Wholesale & retail | 2024 |
| J & J Electrical Installations Ltd | Construction | 2015 |
| J B Electrical (Herts) Ltd | Construction | 2019 |
| J Crouch Electrical Ltd | Construction | 2025 |
| J Hart & SON Limited | Agriculture & fishing | 2013 |
| J R Taxi Rentals Ltd | Transport & logistics | 2013 |
| J W Estates Limited | Real estate | 2002 |
| J West Storage Ltd | Transport & logistics | 2024 |
| J Williams Developments Ltd | Construction | 2025 |
| JA Signalling Ltd | Information & communication | 2020 |
| Jackie Gough Garden Design Limited | Administrative & support | 2010 |
| Jacksons Group Ltd | Construction | 2023 |
| JAL Shoes UK Limited | Wholesale & retail | 2014 |
| James Alexander Electrical Ltd | Construction | 2023 |
| Janesi Limited | Real estate | 2006 |
| Jardinia Group Limited | Administrative & support | 2022 |
| Jasman Consulting International Ltd | Information & communication | 2019 |
| Jaybani Ltd | Real estate | 2026 |
| JB Building Bengeo Ltd | Real estate | 2019 |
| JB Building Enfield Ltd | Real estate | 2019 |
| JB Simmonds Property Limited | Real estate | 2021 |
| Jbaf Limited | Other services | 2022 |
| JBS Cleaners Ltd | Administrative & support | 2025 |
| JC Installations Limited | Information & communication | 2025 |
| JC Roofing Solutions Ltd | Construction | 2022 |
| JCG Air Conditioning Limited | Energy | 2014 |
| JCW Security Ltd | Administrative & support | 2019 |
| JD NDT Ltd | Manufacturing | 2012 |
| JDP Valeting Services Limited | Administrative & support | 2019 |
| JDQ Property Ltd | Real estate | 2026 |
| Jedi Capital Limited | Professional & scientific | 2020 |
| Jeleija Ltd | Information & communication | 2022 |
| Jenyns School Management Company Limited | Professional & scientific | 2006 |
| JES Plastering Ltd | Construction | 2015 |
| Jeya Fastfood Ltd | Hospitality | 2024 |
| JFX Limited | Arts & recreation | 2012 |
| JG Drinks Ltd | Manufacturing | 2016 |
| JG Sport and Injury Rehab Ltd | Arts & recreation | 2019 |
| Jiconsultancy Ltd | Professional & scientific | 2024 |
| Jjcr Property Limited | Administrative & support | 2018 |
| JJS Rail Limited | Professional & scientific | 2018 |
| JK Recruit Ltd | Administrative & support | 2024 |
| JLP Camera Limited | Information & communication | 2017 |
| JM Hair Design Ltd | Construction | 2022 |
| JMC Interiors Limited | Construction | 2019 |
| JMG Transformations Limited | Arts & recreation | 2023 |
| JMM Homes Limited | Real estate | 2021 |
| JMQ Consulting Limited | Information & communication | 2025 |
| JMR Heating Services Ltd | Construction | 2016 |
| JNH Sales Ltd | Real estate | 2017 |
| JO Valant Ltd | Extraterritorial | 2017 |
| Joanna Jane Limited | Arts & recreation | 2011 |
| Jocelyn Consulting Ltd | Professional & scientific | 2017 |
| John Faldo Software Ltd | Information & communication | 2023 |
| John Gilbert & Associates Ltd | Hospitality | 2023 |
| John Grubb Consultants Limited | Professional & scientific | 2012 |
| John Sanders Rodings Limited | Hospitality | 2016 |
| Joma Construction Limited | Construction | 1994 |
| Jonathan Hunt Buntingford Limited | Real estate | 2016 |
| Joshua Benjamin Ltd | Manufacturing | 2023 |
| Joshua Reed Properties Limited | Real estate | 2024 |
| Joshua Wright Consultancy Ltd | Wholesale & retail | 2025 |
| Joth Consultancies Ltd | Construction | 2025 |
| Journey 2 the Soul Ltd | Health & social care | 2025 |
| Joyscroll Limited | Information & communication | 2026 |
| JP Consulting Limited | Information & communication | 2009 |
| JPM Insulations Limited | Construction | 2025 |
| Jpmh Investments Limited | Financial services | 2017 |
| JPR Ellis Electrical Limited | Construction | 2013 |
| JRM Highway Engineers Limited | Construction | 2013 |
| JRP Racing Limited | Wholesale & retail | 2020 |
| JS Complete Builders Ltd | Construction | 2019 |
| JS Woodniture Joinery Ltd | Manufacturing | 2023 |
| JSB Creative Limited | Information & communication | 2026 |
| JSM Logistics Solutions Limited | Transport & logistics | 2022 |
| JT Transport Services Ltd | Transport & logistics | 2024 |
| Juniper Tree & Groundcare Services Ltd | Agriculture & fishing | 2018 |
| Jupiter Hippo Cleaning Limited | Administrative & support | 2023 |
| Jupiter Icsya Ltd | Construction | 2014 |
| Jupiter Jewellery Ltd | Wholesale & retail | 2019 |
| JVS Plumbing & Heating Ltd | Construction | 2019 |
| K J Howe Ltd | Transport & logistics | 2025 |
| K R Adams Cleaning Limited | Administrative & support | 2014 |
| K&F BIM Limited | Construction | 2013 |
| KAI Ramshaw Plastering Limited | Construction | 2016 |
| Kaiapoi Consulting Ltd | Agriculture & fishing | 2013 |
| Kalex Limited | Professional & scientific | 1999 |
| Kambridge Associates Limited | Professional & scientific | 2012 |
| Kane Marketing Limited | Information & communication | 2020 |
| Kappacon Ltd | Administrative & support | 2024 |
| Karate Bestsport UK Ltd | Wholesale & retail | 2020 |
| Kare Creative Limited | Professional & scientific | 2019 |
| Karsten Consultancy Ltd | Professional & scientific | 2024 |
| Katbat Business Intelligence Ltd | Information & communication | 2018 |