| Island Cleaning & Facilities Management Ltd | Administrative & support | 2024 |
| Islanda Ltd | Professional & scientific | 2013 |
| Isyncmusic Limited | Information & communication | 2011 |
| Isyncworld Ltd. | Information & communication | 2013 |
| IT Bromley & Croydon Limited | Information & communication | 2010 |
| ITK Resources Limited | Construction | 2019 |
| Itsher Group Ltd | Other services | 2023 |
| Itsqa Associates Limited | Financial services | 2011 |
| Ivy's Properties Limited | Real estate | 2020 |
| IZ Management Consulting Limited | Information & communication | 2023 |
| J & L Property Services Ltd | Other services | 2019 |
| J & R Electrical Ltd | Construction | 2011 |
| J Couchman Ltd | Professional & scientific | 2013 |
| J Cousins Properties Limited | Real estate | 2019 |
| J K Chicken Ltd | Hospitality | 2022 |
| J P Contract Management Limited | Administrative & support | 2005 |
| J S Motor Repairs Limited | Manufacturing | 2011 |
| J S Warren Limited | Construction | 2009 |
| J Watkins Ltd | Construction | 2021 |
| J.Ferguson Developments Ltd | Real estate | 2022 |
| J.Jenks Ltd | Wholesale & retail | 2023 |
| J.Lugone Limited | Professional & scientific | 2026 |
| J2S Real Estate Ltd | Real estate | 2024 |
| JA Allen Shoes Limited | Wholesale & retail | 2009 |
| JA Building and Construction Limited | Construction | 2020 |
| JA Coaching Ltd | Arts & recreation | 2015 |
| JA Property Developments Limited | Real estate | 2024 |
| Jabeen Estates Limited | Financial services | 2022 |
| Jabeen Investments Ltd | Real estate | 2019 |
| Jabeen Properties LLP | | 2022 |
| Jaboassociates Ltd | Administrative & support | 2023 |
| Jacksons Grooming Room Ltd | Other services | 2021 |
| Jacob's Ladder Ministry CIC | Professional & scientific | 2018 |
| JAI Property Maintenance Ltd | Real estate | 2015 |
| Jaival Solutions Ltd | Information & communication | 2011 |
| Jajkumar Export Limited | Wholesale & retail | 2025 |
| Jaky Ltd | Transport & logistics | 2020 |
| Jam-Hair Sanderstead Ltd | Other services | 2009 |
| James Hughes Consultancy Ltd | Real estate | 2022 |
| James Winney Limited | Construction | 2009 |
| JAN Hair & Beauty Limited | Other services | 2020 |
| JAN2TOIT Limited | Administrative & support | 2026 |
| Japk Ltd | Construction | 2025 |
| Jaya Property Group Ltd | Real estate | 2024 |
| Jaynak Healthcare Limited | Health & social care | 2025 |
| JBJ Autorepairs Limited | Transport & logistics | 2005 |
| JC Carpentry Services Limited | Construction | 2007 |
| JCA Tapas Ltd | Hospitality | 2020 |
| Jcbs Heating Limited | Construction | 2018 |
| JD Business Solutions Ltd | Professional & scientific | 2009 |
| Jdub Investments Ltd. | Hospitality | 2014 |
| Jdwp Analytics Ltd | Information & communication | 2026 |
| Jeanaanii Ltd | Real estate | 2023 |
| Jega & Brother Ltd | Hospitality | 2021 |
| Jellico Computer Services Ltd. | Information & communication | 1995 |
| Jemicen Ltd | Wholesale & retail | 2025 |
| Jemmietomlay Ltd | Wholesale & retail | 2023 |
| Jenny Lemon Ltd | Manufacturing | 2017 |
| Jenny Lind Limited | Administrative & support | 2002 |
| Jeroen Hoppe Property Limited | Real estate | 2023 |
| Jevan ALI Productions Ltd | Information & communication | 2012 |
| JH Bay Ltd | Construction | 2025 |
| JH Payroll Limited | Other services | 2018 |
| Jhmn London Limited | Professional & scientific | 2014 |
| Jhos Broadcast Ltd | Information & communication | 2026 |
| Jinks Property Ltd | Real estate | 2012 |
| JJ Francis Properties Ltd | Real estate | 2026 |
| JJ Retreats International Ltd | Administrative & support | 2014 |
| JJ Web Solutions Limited | Wholesale & retail | 2011 |
| JJC Partners Limited | Professional & scientific | 2021 |
| JJH Technical Ltd | Professional & scientific | 2025 |
| Jjnb Ltd | Other services | 2020 |
| JK2 Developments Limited | Real estate | 2020 |
| Jkvc Ltd | Wholesale & retail | 2023 |
| JL Proclean Supply and Services Ltd | Administrative & support | 2026 |
| Jlr-Uk Limited | Construction | 2025 |
| JMC Care Ltd | Administrative & support | 2018 |
| JMH Consulting Ltd | Professional & scientific | 2023 |
| JMH Developments Ltd | Real estate | 2025 |
| JMR Designes Ltd | Professional & scientific | 2013 |
| JOE Lucas Carpentry Ltd | Manufacturing | 2021 |
| John Woods & Associates Limited | Financial services | 1999 |
| Johnson SMS Limited | Information & communication | 2016 |
| Johnston & Johnston Limited | Health & social care | 2002 |
| Jolly Joker Ltd | Other services | 2019 |
| JON COX Ltd | Hospitality | 2026 |
| Jordan Cave Coaching Limited | Other services | 2019 |
| Jorge Khawam Studio Ltd | Professional & scientific | 2024 |
| Joseph B Properties Limited | Real estate | 2024 |
| Josephs Manor Ltd | Arts & recreation | 2024 |
| Joshvic Tutor Ltd | Education | 2021 |
| Josoemag Services Ltd | Information & communication | 2011 |
| Jothhsb Ltd | Hospitality | 2022 |
| Journeying Support Services Limited | Health & social care | 2022 |
| Journeys & Voyages London Limited | Administrative & support | 2014 |
| Jovani Catering Ltd | Hospitality | 2023 |
| Joweny Ltd | Health & social care | 2023 |
| Joyful Abode Ltd | Health & social care | 2026 |
| Joyful Jars Ltd | Manufacturing | 2024 |
| JP Pronto Logistics Ltd | Transport & logistics | 2020 |