| Iterive Ltd | Information & communication | 2025 |
| Ithax Consulting Services Ltd | Information & communication | 2021 |
| Itqube Ltd | Information & communication | 2023 |
| Ivanas Pizza Ltd | Hospitality | 2022 |
| Ivisa Global Limited | Administrative & support | 2022 |
| IVM Consulting Ltd | Professional & scientific | 2024 |
| J & J Consultancy (2010) Limited | Information & communication | 2011 |
| J B Garrard Ltd | Wholesale & retail | 2010 |
| J B Lord Limited | Wholesale & retail | 2021 |
| J T P London Ltd | Wholesale & retail | 2020 |
| J&A Concert Pianists Ltd | Education | 2020 |
| J&M Mortgage Solutions Ltd | Financial services | 2021 |
| Jabez Publishing Ltd | Wholesale & retail | 2019 |
| Jack Windows Limited | Other services | 2018 |
| Jact Studio Ltd | Manufacturing | 2024 |
| Jagtar Gill Limited | Health & social care | 2011 |
| JAM City Developments Ltd | Construction | 2018 |
| James Muggoch Ltd | Manufacturing | 2023 |
| Jannah & Mikail Ltd | Information & communication | 2011 |
| Japanese Bakery London Ltd | Manufacturing | 2020 |
| JAR Construction Carpentry and Joinery Ltd | Construction | 2016 |
| Javid Asset Management Limited | Financial services | 2025 |
| Jaysnacks Ltd | Wholesale & retail | 2025 |
| JB Paving Ltd | Construction | 2019 |
| JB80 Ltd | Wholesale & retail | 2018 |
| JBS Fish & Seafood Limited | Wholesale & retail | 2023 |
| JBS Fish Suppliers Limited | Wholesale & retail | 2017 |
| JBW Cleaning Services Limited | Administrative & support | 2024 |
| JC Diva Ltd | Wholesale & retail | 2021 |
| JC Renovations Ltd | Construction | 2013 |
| JC Retro Ltd | Wholesale & retail | 2025 |
| JC Zora Ltd | Wholesale & retail | 2025 |
| JCD Holdings Limited | Real estate | 2023 |
| Jcdc Management Company Limited | Administrative & support | 2007 |
| Jcdecaux Small Cells Limited | Professional & scientific | 2014 |
| JCQ Capital Management Ltd | Professional & scientific | 2024 |
| JD Ukconsulting Ltd | Information & communication | 2021 |
| Jdimedia Ltd | Information & communication | 2025 |
| JDX Developers Limited | Construction | 2025 |
| Jednac Construction Limited | Construction | 2006 |
| JEM Maintenance Limited | Administrative & support | 2017 |
| Jerina Ltd | Health & social care | 2013 |
| JES Estates UK LLP | | 2015 |
| JFP Lighting Ltd | Administrative & support | 2021 |
| Jgillconsultancy Ltd | Administrative & support | 2024 |
| Jgsk Limited | Construction | 2014 |
| JH Autocare Ltd | Wholesale & retail | 2026 |
| Jhanvi Properties Ltd | Real estate | 2020 |
| Jifri & Partners Ltd | Other services | 2024 |
| Jigsaw Piece Productions Limited | Information & communication | 2017 |
| Jinendra Solutions Ltd | Information & communication | 2018 |
| Jiostar UK Limited | Administrative & support | 1991 |
| JJ & K Properties Ltd | Real estate | 2025 |
| JJQ Ltd. | Wholesale & retail | 2018 |
| JK Universal Holdings Limited | Financial services | 2019 |
| JKS West London Shotokan Karate Ltd | Arts & recreation | 2023 |
| JMG Pictures Limited | Information & communication | 2023 |
| Joben Consulting Limited | Professional & scientific | 2016 |
| Jobi Enterprises Limited | Information & communication | 2019 |
| Jodeb Cleaning Limited | Extraterritorial | 2017 |
| Jodeb Waste Management Services Ltd | Water & waste | 2026 |
| Johal & Company Accountants Limited | Professional & scientific | 2016 |
| Johalandco.Com Limited | Professional & scientific | 2012 |
| John E Collins Ltd | Education | 2024 |
| John's Boat Works Ltd | Manufacturing | 2011 |
| Joinex Joinery Express Limited | Manufacturing | 2012 |
| Jolly Boutique Ltd | Wholesale & retail | 2023 |
| Jonny Properties Ltd | Real estate | 2022 |
| Jonrick Limited | Health & social care | 2014 |
| Journalise Ltd | Wholesale & retail | 2022 |
| Jowhar Limited | Transport & logistics | 2026 |
| Joypoint Ltd | Wholesale & retail | 2022 |
| JR & DR Properties Ltd | Construction | 2021 |
| JR Dimbiz Limited | Extraterritorial | 2016 |
| Jsan Consulting Limited | Information & communication | 2016 |
| JSB Global Consulting Limited | Administrative & support | 2019 |
| Jsgi Limited | Wholesale & retail | 2019 |
| JT 4 HR Limited | Administrative & support | 2017 |
| Juannde Ltd | Professional & scientific | 2021 |
| Jude HUE Limited | Manufacturing | 2024 |
| Julias Ginger Bubbles Ltd | Manufacturing | 2025 |
| Juniper Capital Ltd | Real estate | 2020 |
| Jupiter 1 Ltd | Wholesale & retail | 2025 |
| Jupiter Direct Consultancy Ltd | Professional & scientific | 2024 |
| Just a TAD Ltd | Extraterritorial | 2021 |
| Just Because Beauty Therapy Ltd | Other services | 2022 |
| Jvjo Ltd | Administrative & support | 2020 |
| JWM Ceilings Limited | Construction | 2021 |
| K H Claims Management Limited | Professional & scientific | 1996 |
| K H Holdings Limited | Extraterritorial | 1998 |
| K N Pro ADS Ltd | Professional & scientific | 2025 |
| K Papastamatis Building Contractors Ltd | Construction | 2004 |
| K.L. Financial Solutions Limited | Professional & scientific | 2008 |
| K1 Motors Ltd | Wholesale & retail | 2017 |
| K2 Bespoke Project Ltd | Construction | 2017 |
| K2P Infotech Ltd | Information & communication | 2017 |
| Kabusha Ltd | Other services | 2018 |
| Kadware Ltd | Information & communication | 2016 |
| Kahiye Capital Limited | Professional & scientific | 2022 |
| Kaizentech Consulting Limited | Wholesale & retail | 2024 |