| J Hinton Medical Limited | Health & social care | 2025 |
| J Hoskin Consulting Limited | Professional & scientific | 2021 |
| J M Addo & Sons (UK) Limited | Real estate | 2014 |
| J M Robinson (Halesowen) Limited | Health & social care | 2003 |
| J N Simaria & Co Services Ltd | Extraterritorial | 2004 |
| J&A Building Solutions Limited | Construction | 2009 |
| J&A Health Ltd | Wholesale & retail | 2022 |
| J&E Group Holdings Ltd | Real estate | 2017 |
| J. Roig & Co. Limited | Wholesale & retail | 1984 |
| J.S.A Health Limited | Health & social care | 2017 |
| J47 Limited | Hospitality | 2023 |
| Jaak Property Tech Ltd | Real estate | 2025 |
| Jacob and Thomson Limited | Information & communication | 2023 |
| Jacomo Commercial Limited | Other services | 2016 |
| Jacomo Limited | Real estate | 2012 |
| Jadebar Limited | Real estate | 2020 |
| Jagg Fitness London Limited | Arts & recreation | 2021 |
| JAI Ambe Properties Limited | Real estate | 2024 |
| Jain House Ltd | Real estate | 2016 |
| Jain Surgical Limited | Health & social care | 2022 |
| Jain Vishva Bharati London | Other services | 2004 |
| Jainim Ltd | Real estate | 2019 |
| Jaisomnath Ltd | Information & communication | 2011 |
| Jaiventures Limited | Real estate | 2016 |
| JAK Specialists Ltd | Administrative & support | 2023 |
| Jake JF Murphy Ltd | Construction | 2024 |
| Jalaram Nivas Limited | Real estate | 2018 |
| Jalaram Properties Ltd | Real estate | 2024 |
| Jamen Jones Limited | Extraterritorial | 2008 |
| James House (Northwood) Ltd | Real estate | 2023 |
| James Little Piano Tuning Limited | Wholesale & retail | 2013 |
| Janco Consulting Ltd | Real estate | 2015 |
| Janco Finance Ltd | Financial services | 2018 |
| Janco Ltd | Information & communication | 2020 |
| Janco Properties Limited | Real estate | 2016 |
| Jannah Jasmine Perfumes Limited | Wholesale & retail | 2021 |
| Janred Court (Holden Road) Limited | Households | 1976 |
| Jaran Properties Ltd | Real estate | 2011 |
| Jardine Brook Solutions Ltd | Professional & scientific | 2012 |
| Jarock Properties Limited | Real estate | 2017 |
| Jarock Subsidiary Limited | Real estate | 2026 |
| Jarp Enter Ltd | Wholesale & retail | 2026 |
| Jarr Homes Ltd | Real estate | 2021 |
| Jasel Limited | Real estate | 2015 |
| Jasmine Party Hall Ltd | Hospitality | 2025 |
| Jason Moore Photography Limited | Professional & scientific | 2011 |
| Jastaig Builders & Contractors Limited | Construction | 2022 |
| JAX Projects London Ltd | Construction | 2022 |
| JAY Ambe London Limited | Wholesale & retail | 2013 |
| JAY Connect Ltd | Information & communication | 2025 |
| Jaya Holdings Ltd | Real estate | 2019 |
| Jaylink Ltd | Professional & scientific | 2025 |
| Jazz's Trading Ltd | Transport & logistics | 2020 |
| JB Executive Coaching Limited | Professional & scientific | 2008 |
| JBM & Sons Ltd | Construction | 2021 |
| JBS Development and Construction Limited | Construction | 2017 |
| Jbson Consulting Ltd | Professional & scientific | 2020 |
| Jbson Properties Ltd | Real estate | 2020 |
| Jbstec Limited | Information & communication | 2010 |
| JBT Holidays Ltd | Administrative & support | 2013 |
| JCM B2B Ltd | Wholesale & retail | 2025 |
| JCO Construction Ltd | Construction | 2019 |
| JD & AB Properties Limited | Real estate | 2021 |
| JDA Drainage Services Ltd | Water & waste | 2023 |
| Jdal Limited | Arts & recreation | 2025 |
| JDB Life Ltd | Financial services | 2012 |
| Jeet Tailor Design Ltd | Professional & scientific | 2016 |
| Jegan Invest Ltd | Real estate | 2019 |
| Jemajo Limited | Professional & scientific | 2026 |
| Jems Property Maintenance Ltd | Construction | 2019 |
| Jems Recruitment Limited | Administrative & support | 2008 |
| JEN Consulting Limited | Professional & scientific | 2010 |
| JEN Risk Consulting Ltd | Professional & scientific | 2013 |
| Jericho Pharma Limited | Wholesale & retail | 2021 |
| Jerjas Limited | Information & communication | 2013 |
| Jesap Ltd | Administrative & support | 2025 |
| Jewellery Advisory Services Limited | Professional & scientific | 1998 |
| Jewellery With Love Ltd | Wholesale & retail | 2020 |
| Jexcom Limited | Other services | 2010 |
| JG Costello Limited | Construction | 2025 |
| JGM Construction Ltd | Construction | 2016 |
| Jhanji Consultancy Ltd | Professional & scientific | 2014 |
| Jhudha Home Improvements Limited | Administrative & support | 2012 |
| JIB Holdings Ltd | Real estate | 2019 |
| Jiefeng UK Ltd | Wholesale & retail | 2021 |
| Jigsaw Change Consulting Ltd | Professional & scientific | 2019 |
| JIT Property Investments Limited | Real estate | 2021 |
| JJ Electrics Residential Limited | Construction | 2026 |
| JJ Realty Ltd | Real estate | 2016 |
| JJ Rowlands Limited | Financial services | 2021 |
| Jjan Ltd | Hospitality | 2024 |
| Jjones Holdings Limited | Administrative & support | 2023 |
| JJP Financial Ltd | Financial services | 2018 |
| JK Immobilia Limited | Real estate | 2019 |
| JKD Locum Limited | Health & social care | 2022 |
| JLR Project Consulting Ltd | Administrative & support | 2011 |
| JM Autohaus Limited | Wholesale & retail | 2023 |
| JM Consults Ltd | Information & communication | 2023 |
| JMR Associates Limited | Professional & scientific | 2026 |
| JMS Statistics Ltd | Professional & scientific | 2015 |