| J Hangan Ltd | Transport & logistics | 2025 |
| J Humphrey Engineering Ltd | Construction | 2016 |
| J K H D Limited | Professional & scientific | 2004 |
| J Land Limited | Real estate | 2018 |
| J M Drylining Ltd | Construction | 2010 |
| J M Ireland Limited | Construction | 2014 |
| J OBI Construction Ltd | Construction | 2018 |
| J P 1 Homes Ltd | Real estate | 2020 |
| J P C Mulligan Properties Limited | Real estate | 2011 |
| J P Eagles Ltd | Real estate | 2022 |
| J Pillai Real Estate Ltd | Real estate | 2024 |
| J Pitt Enterprises Ltd | Other services | 2016 |
| J Rayfield Services Limited | Construction | 2011 |
| J S Entreprise Ltd | Wholesale & retail | 2020 |
| J S N Fireaway Ltd | Hospitality | 2020 |
| J S Uppal Limited | Construction | 2025 |
| J Ward Drives & Patios Ltd | Construction | 2019 |
| J Woods Consultants Limited | Construction | 2008 |
| J&B Construction Limited | Construction | 2011 |
| J&B Global Ltd | Professional & scientific | 2025 |
| J&J Consults Limited | Professional & scientific | 2016 |
| J&K Security Limited | Administrative & support | 2014 |
| J&O Studio Limited | Other services | 2017 |
| J&S Bains Ltd | Real estate | 2024 |
| J&S Haulage Ltd | Transport & logistics | 2020 |
| J&S Retail Ltd | Wholesale & retail | 2018 |
| J&T Associates (Estates) Limited | Construction | 2024 |
| J-Kent Solutions UK Limited | Wholesale & retail | 2013 |
| J. & a. Builders Limited | Construction | 1960 |
| J. Lord's Cleaning Services Limited | Administrative & support | 2018 |
| J. Muir Properties Limited | Real estate | 2020 |
| J.A.S. Fabrication & Welding Services Ltd | Manufacturing | 2013 |
| J.A.Sian Limited | Real estate | 2018 |
| J.D.R. Design and Build Ltd | Manufacturing | 2009 |
| J.K. Auto Trading Ltd | Wholesale & retail | 2026 |
| J.K. Romeo Ltd | Construction | 2017 |
| J.O. Global Merchants Ltd | Wholesale & retail | 2026 |
| J.R Visualist Ltd | Information & communication | 2019 |
| J.S.W. (Kent) Limited | Manufacturing | 2010 |
| J.T.Kemsley(London)Limited | Financial services | 1947 |
| J5 Capital Ltd | Financial services | 2017 |
| J5 Lease Ltd | Administrative & support | 2024 |
| J5 Property Ltd | Real estate | 2024 |
| J777 Group Limited | Professional & scientific | 2020 |
| JA Brothers Property Ltd | Real estate | 2025 |
| JA Consultancy & Development Ltd | Real estate | 2023 |
| JA Wealth Ltd | Real estate | 2025 |
| Jaatram Transport Ltd | Transport & logistics | 2025 |
| JAB Civil Engineering Ltd | Other services | 2020 |
| Jabbasolutions Limited | Information & communication | 2025 |
| JAC Skip Hire Limited | Water & waste | 2015 |
| Jachin and Boaz Mini Mart Ltd | Wholesale & retail | 2024 |
| Jackaman INS Services Ltd | Financial services | 2017 |
| Jackson Survey & Volumetric Services Limited | Construction | 2011 |
| Jackster Transport Limited | Transport & logistics | 2019 |
| Jacobs Electrical Services Ltd | Energy | 2014 |
| Jacques Alain Ltd | Construction | 2025 |
| Jacs Services Ltd | Construction | 2015 |
| JAG Assets Investments Ltd | Real estate | 2025 |
| Jagmani Limited | Wholesale & retail | 2024 |
| Jagmar Ltd | Transport & logistics | 2024 |
| Jagraj Singh Ltd | Wholesale & retail | 2025 |
| Jags Property Group Ltd | Real estate | 2019 |
| Jagson Group Limited | Construction | 2023 |
| JAI Construction Ltd | Construction | 2015 |
| Jaisiyaram Limited | Real estate | 2022 |
| JAJ Signals Limited | Professional & scientific | 2018 |
| JAK Healthcare Services Ltd | Health & social care | 2019 |
| Jake Barber 2 Ltd | Other services | 2025 |
| Jake Barber Ltd | Other services | 2024 |
| Jaks Accounting Ltd | Professional & scientific | 2018 |
| JAL Property Investments Ltd | Real estate | 2024 |
| James & Shaw Ltd | Construction | 2019 |
| James Anthony Interiors Ltd | Construction | 2010 |
| James Jordan Ltd | Real estate | 2021 |
| James More Magic Ltd | Arts & recreation | 2015 |
| James Rosa Associates Limited | Financial services | 2010 |
| Jams Electrical Ltd | Energy | 2019 |
| Janda Court Residents' Association Limited | Households | 1978 |
| Jandoo Holdings Ltd | Financial services | 2023 |
| Jandoo Properties Ltd | Real estate | 2024 |
| JANET21 Limited | Professional & scientific | 2017 |
| Janiz Ltd | Financial services | 2019 |
| Jannat Construction Work Ltd | Construction | 2024 |
| Janson Projects Limited | Construction | 2008 |
| Janta Developments Ltd | Administrative & support | 2019 |
| Janusz Swiatek Transport Ltd | Transport & logistics | 2026 |
| JAS Investment Property Limited | Real estate | 2023 |
| Jaskirat Construction Ltd | Construction | 2020 |
| Jasmine Translogistic Limited | Transport & logistics | 2022 |
| Jason Agar Limited | Professional & scientific | 2017 |
| Jason Ralph London Limited | Manufacturing | 2023 |
| Jason Woolcock Productions Ltd | Arts & recreation | 2013 |
| Jason's Pro Paintworks Ltd | Construction | 2025 |
| Jawani Jewels Limited | Wholesale & retail | 2025 |
| JAX Building & Landscaping Limited | Construction | 2020 |
| JAY & VIJ Ltd | Real estate | 2024 |
| JAY KAY Construction Services Limited | Construction | 2020 |
| JAY KAY Trading (Gravesend) Limited | Wholesale & retail | 2024 |
| JAY R B Ltd | Real estate | 2023 |