| IAN Dutnall Limited | Information & communication | 2003 |
| IAN Smith Media Limited | Information & communication | 2012 |
| Iana Ltd | Real estate | 2025 |
| ICB Advisory Limited | Professional & scientific | 2018 |
| Icelandic Snow OWL Industries Ltd | Information & communication | 2015 |
| Icon Luxury Transport Limited | Transport & logistics | 2014 |
| Icon Travel Limited | Administrative & support | 2012 |
| IDU UK Limited | Information & communication | 2016 |
| Ifrms Ltd | Hospitality | 2010 |
| Ignatiou Investments Ltd | Hospitality | 2025 |
| Ignite ME Workshop Theatre C.I.C. | Arts & recreation | 2017 |
| Iken Energy Limited | Mining & quarrying | 2017 |
| IM Sales Consulting Ltd | Professional & scientific | 2024 |
| Image Science Consulting Limited | Extraterritorial | 2011 |
| Imagine-Talent Consultancy Limited | Professional & scientific | 2015 |
| Imatch Mortgages Limited | Financial services | 2002 |
| Imatch Property Limited | Real estate | 2020 |
| Imko Property Development Ltd | Construction | 2012 |
| IMP Chin Limited | Information & communication | 2025 |
| Impact Broadcast Ltd. | Information & communication | 2023 |
| Imperial RAM Design Limited | Other services | 1989 |
| Imperial Teddington Ltd | Hospitality | 2025 |
| Imprintcapital Ltd | Construction | 2015 |
| IN Agency Ltd | Professional & scientific | 2026 |
| IN Divine Response to Your Word Lord | Professional & scientific | 2008 |
| IN Pursuit of Luxury Limited | Information & communication | 2023 |
| Inbastion Limited | Information & communication | 2025 |
| Inconceivable Pictures Ltd | Information & communication | 2025 |
| Independent Project Management & Consulting Ltd | Professional & scientific | 2002 |
| Independent Sourcing and Supplies Limited | Wholesale & retail | 2010 |
| Indigo Event Services Ltd | Administrative & support | 2025 |
| Indigo Quest Automotive Limited | Professional & scientific | 2024 |
| Ingarangi Ltd | Extraterritorial | 2010 |
| Innior Ltd | Other services | 2024 |
| Innovatus Drinks Limited | Financial services | 2022 |
| Innovexa Consulting Ltd | Professional & scientific | 2025 |
| Inobec Technologies Limited | Professional & scientific | 2022 |
| Inps Consulting Ltd | Information & communication | 2013 |
| Inspira Marketing Limited | Professional & scientific | 2021 |
| Inspired Sharing Limited | Information & communication | 2025 |
| Instant Opera Limited | Education | 2017 |
| Integrated Experience Limited | Information & communication | 2016 |
| Integration Education and Consulting Ltd | Education | 2024 |
| Intelligencer Limited | Professional & scientific | 2016 |
| Intelligent Imaging Innovations Ltd | Administrative & support | 2016 |
| Intent Foreign Education & Project Consultancy Ltd | Wholesale & retail | 2021 |
| Interiors by Heirloom Limited | Wholesale & retail | 2005 |
| International A&A Ltd | Energy | 2025 |
| International Graphics Engineering Limited | Professional & scientific | 2022 |
| International Servicing Ltd | Financial services | 2020 |
| Ionising Radiation Metrology Consultants Limited | Professional & scientific | 2002 |
| IPA Architects Limited | Professional & scientific | 2002 |
| Iplant Landscape Limited | Professional & scientific | 2008 |
| Iplant Limited | Professional & scientific | 2008 |
| IRB Autarky Limited | Professional & scientific | 2016 |
| ISTA369 Ltd | Hospitality | 2026 |
| Itabashi Limited | Administrative & support | 2015 |
| ITC Network Limited | Administrative & support | 1991 |
| Ithaka Design Limited | Construction | 2023 |
| Ithaka House GCR Limited | Construction | 2024 |
| Ithaka House Limited | Construction | 2022 |
| ITL Data and Databases Limited | Information & communication | 2022 |
| Itree Consultancy Limited | Professional & scientific | 2007 |
| Itree Limited | Professional & scientific | 2007 |
| J & B Painting & Decorating Limited | Construction | 2004 |
| J & K Building Limited | Construction | 2023 |
| J Atkinson Consulting Ltd | Professional & scientific | 2019 |
| J B Sound Ltd | Information & communication | 2005 |
| J Coombes Investments Limited | Real estate | 2023 |
| J G S Structural Thinking Limited | Professional & scientific | 2005 |
| J M Lowe Properties Limited | Real estate | 1961 |
| J P Dunn Construction Holdings Limited | Financial services | 2024 |
| J P Dunn Construction Limited | Construction | 1999 |
| J&K Heating & Plumbing Limited | Construction | 2017 |
| J&Sl Ltd | Information & communication | 2020 |
| J. P. Peel & Co Limited | Professional & scientific | 2012 |
| J. S. & a. Petrou Holdings Limited | Financial services | 2023 |
| J. S. & a. Petrou Limited | Financial services | 2023 |
| J.Leon Consultancy Ltd | Professional & scientific | 2020 |
| Jacaranda Collection Limited | Wholesale & retail | 2017 |
| Jack Restoration Ltd | Construction | 2015 |
| Jack's Place Training Limited | Professional & scientific | 2026 |
| Jackson Plating Ltd | Manufacturing | 2003 |
| Jackson-Stops & Staff (Country Houses) Limited | Real estate | 1992 |
| Jacob and Partner Ltd | Hospitality | 2022 |
| Jacob's Since 1932 Ltd | Hospitality | 2017 |
| James Thorp Consulting Limited | Information & communication | 2019 |
| JAN Lloyd Consulting Ltd | Other services | 2017 |
| Jandaya Limited | Information & communication | 2016 |
| Jane Kell Ltd | Wholesale & retail | 2022 |
| Japan UK Art and Museum Limited | Education | 2007 |
| Jasma Ltd | Households | 2021 |
| Jason Andrew Heating Solutions Limited | Professional & scientific | 2013 |
| Jason Berwick IT Limited | Information & communication | 2017 |
| Jason Martin Studios Limited | Information & communication | 2012 |
| Jayes Fernandez Property Investment 2 Ltd | Real estate | 2026 |
| JBL Certification UK Limited | Other services | 2020 |
| Jbmr Electrical Ltd | Construction | 2020 |
| JBS Fulfilment Limited | Administrative & support | 2006 |
| Jean Burke Consulting Limited | Health & social care | 2013 |