| Jahangir Warraich Ltd | Wholesale & retail | 2024 |
| Jain's Astrology Ltd | Professional & scientific | 2022 |
| Jairus Care Ltd | Health & social care | 2023 |
| Jaiz Online Projects Limited | Manufacturing | 2021 |
| JAM01 Trading Ltd | Transport & logistics | 2018 |
| James & James Associates Ltd | Health & social care | 2017 |
| Jamm Toast Limited | Professional & scientific | 2025 |
| JAN Consultancy Services Ltd | Information & communication | 2018 |
| Janan Trade Ltd | Financial services | 2026 |
| Jani Building Services Ltd | Construction | 2015 |
| Jannah Cars Ltd | Wholesale & retail | 2025 |
| Jannet Security Limited | Administrative & support | 2025 |
| Jannet Security Services Ltd | Administrative & support | 2015 |
| Jason Bros Construction Ltd | Construction | 2025 |
| JAT Services Limited | Administrative & support | 2005 |
| Java Links Limited | Wholesale & retail | 2025 |
| Javaid & Co Holdings Ltd | Financial services | 2021 |
| Javaid & Sons Retail Ltd | Wholesale & retail | 2026 |
| Javaid Investment London Ltd | Real estate | 2021 |
| JAY Immigration Lawyers Limited | Professional & scientific | 2024 |
| JAY Laxmiji Limited | Real estate | 2022 |
| Jays London Limited | Wholesale & retail | 2015 |
| Jazmah Trading Ltd | Transport & logistics | 2025 |
| Jazz Cars Ltd | Wholesale & retail | 2012 |
| Jazz for Babies Ltd | Information & communication | 2013 |
| JB Roofing Supplies Ltd | Construction | 2025 |
| Jbatts Capital Ltd | Real estate | 2023 |
| JBM UK Services Ltd | Construction | 2026 |
| JBS Electrical Ltd | Construction | 2015 |
| JD Rotariu Ltd | Construction | 2019 |
| JDA Utility Ltd | Construction | 2018 |
| Jenbay Limited | Information & communication | 2018 |
| Jendaya Limited | Professional & scientific | 2018 |
| Jennymenz Limited | Professional & scientific | 2014 |
| Jerone B Music Ltd | Information & communication | 2021 |
| Jerry Fabrications Ltd | Manufacturing | 2024 |
| Jessie Holds Ltd | Financial services | 2025 |
| JET Agent Ltd | Manufacturing | 2019 |
| Jetour Auto Limited | Wholesale & retail | 2025 |
| Jetour Group Limited | Wholesale & retail | 2025 |
| Jevko Services Ltd | Construction | 2017 |
| JF Media Ltd | Information & communication | 2024 |
| JGM Studio Ltd | Arts & recreation | 2026 |
| Jiavani Enterprises Ltd | Health & social care | 2018 |
| Jihaan Ltd | Professional & scientific | 2010 |
| Jimmy MDK Ltd | Transport & logistics | 2025 |
| Jimmy's Dream Properties Ltd | Real estate | 2023 |
| Jinnah Foundation | Education | 2016 |
| JJA Trading Ltd | Transport & logistics | 2021 |
| JL Central Limited | Households | 2024 |
| JL Homeland Limited | Real estate | 2021 |
| JL United Limited | Real estate | 2014 |
| JMS Care Limited | Administrative & support | 2023 |
| JN Build Ltd | Construction | 2016 |
| JNK Build Ltd | Construction | 2020 |
| Jo-Jaden Building Services Limited | Construction | 2010 |
| Joan Myers Consultancy Ltd | Professional & scientific | 2020 |
| Jobtrial Ltd | Information & communication | 2019 |
| Joeallan Holdings Ltd | Financial services | 2023 |
| Joeallan Limited | Other services | 2009 |
| Joeallan Property Investment Ltd | Real estate | 2023 |
| John Aladejare Healthcare Limited | Health & social care | 2013 |
| John O'Mahony Limited | Construction | 2014 |
| Joined UP Whiting Ltd | Professional & scientific | 2024 |
| Jomi Solutions Ltd | Professional & scientific | 2016 |
| Jonser Ltd | Real estate | 2017 |
| Josba Healthcare Service Limited | Health & social care | 2015 |
| Joseph's Patisserie Limited | Hospitality | 2026 |
| Josephs Wigs Ltd | Other services | 2015 |
| Josh Hair and Beauty Limited | Extraterritorial | 2018 |
| Jovial Investments Ltd | Households | 2023 |
| JP Marpha Limited | Hospitality | 2021 |
| JPB Lofts and Extensions Limited | Construction | 2016 |
| Jpmp Property Limited | Real estate | 2018 |
| JS Blue Ltd | Health & social care | 2024 |
| JS Site Solutions Ltd | Construction | 2020 |
| Jsms Trading Limited | Real estate | 2018 |
| JSZ PVT Trading Ltd | Transport & logistics | 2018 |
| JT London Property Services LLP | | 2021 |
| Jugari Limited | Wholesale & retail | 2025 |
| Jugmag Ltd | Information & communication | 2015 |
| Juice London Limited | Professional & scientific | 2014 |
| Just Breathe Fitness Ltd | Other services | 2018 |
| Just Cakes Limited | Manufacturing | 2019 |
| Just Vends Ltd | Hospitality | 2025 |
| Justone Design Ltd | Professional & scientific | 2025 |
| JVC Global Ltd | Professional & scientific | 2025 |
| JW MEP Planning Services Limited | Professional & scientific | 2026 |
| K & P Devenish Limited | Administrative & support | 2013 |
| K P Builders (UK) Limited | Real estate | 2006 |
| K&B Investment Property Ltd | Real estate | 2024 |
| K&F Developments Limited | Real estate | 2019 |
| K&K Catering Limited | Other services | 2017 |
| K&K Consultancy and Business Management Limited | Information & communication | 2013 |
| K&M Business Consultancy Ltd | Professional & scientific | 2022 |
| K. Edward Road Surgery Property Ltd | Real estate | 2026 |
| K. Mohamud Enterprise Ltd | Health & social care | 2025 |
| K.Mohammed's Medical Services Ltd | Health & social care | 2013 |
| K2 Engineering & Energy Ltd | Professional & scientific | 2017 |
| K8 Clinical Consulting Ltd | Professional & scientific | 2025 |