| Infinity Imex Limited | Wholesale & retail | 2025 |
| Infinity Records Limited | Manufacturing | 2023 |
| Info-System (UK) Ltd | Information & communication | 2004 |
| Inforcer Ltd | Information & communication | 2022 |
| Inform Engineering Ltd | Professional & scientific | 2016 |
| Information Centre and Shop (Hudson House) Limited | Real estate | 2021 |
| Infospaces Limited | Professional & scientific | 2000 |
| Infra-Analytics Limited | Professional & scientific | 2016 |
| Inframe 051 Limited | Real estate | 2020 |
| Infrasolute UK Limited | Manufacturing | 2023 |
| Infrastructure and Energy Finance Consulting Ltd | Professional & scientific | 2026 |
| Infrastructure Procurement Services Limited | Professional & scientific | 2014 |
| Ingolf Limited | Administrative & support | 2001 |
| Initiatives in Design Limited | Professional & scientific | 2007 |
| Innishannon Developments Limited | Construction | 2016 |
| Inno Properties Limited | Construction | 2024 |
| Innovate Access Solutions Ltd | Construction | 2020 |
| Innovate and Educate Ltd | Wholesale & retail | 2022 |
| Innovez Limited | Information & communication | 2004 |
| Inprudea Ltd. | Information & communication | 1999 |
| Inside Matters Ltd | Wholesale & retail | 2019 |
| Insidezone Limited | Health & social care | 2004 |
| Insiem Ltd | Other services | 2020 |
| Insight Health Economics Limited | Professional & scientific | 2009 |
| Insight Health Improvement Ltd | Professional & scientific | 2017 |
| Inspired Interiors Design & Installation Limited | Construction | 2014 |
| Inspires Performance and Wellbeing Ltd | Information & communication | 2016 |
| Instant Finance Partners Ltd | Financial services | 2019 |
| Instant Sourcing Limited | Administrative & support | 2008 |
| Insurance Services (Surrey) Limited | Financial services | 1973 |
| Insureai Limited | Professional & scientific | 2019 |
| Intara Space Limited | Other services | 2025 |
| Intechra Consulting Limited | Wholesale & retail | 2003 |
| Integra Management Limited | Financial services | 1997 |
| Integrated Camera Systems Ltd | Administrative & support | 2013 |
| Integrated Polymer Systems (Northern) Limited | Construction | 2000 |
| Integrated Polymer Systems Limited | Construction | 1985 |
| Integrity Crisis Preparedness Ltd | Professional & scientific | 2024 |
| Integrix XXI Limited | Manufacturing | 1998 |
| Integwise Ltd | Information & communication | 2017 |
| Inteletravel UK Holdings Limited | Financial services | 2024 |
| Inteletravel UK Limited | Administrative & support | 2017 |
| Intelligence Accelerated Limited | Professional & scientific | 2026 |
| Intelliquick Solutions Ltd | Real estate | 2019 |
| Interglobe Freight Services Limited | Transport & logistics | 1996 |
| Interlogistica Ltd. | Transport & logistics | 2018 |
| International Centre of Education and Innovation Limited | Professional & scientific | 2023 |
| International Chauffeurs Limited | Transport & logistics | 2009 |
| International Computer Systems (London) Limited | Real estate | 1978 |
| International Pipeline Products Limited | Manufacturing | 1984 |
| Internet Consultancy Ltd | Information & communication | 2009 |
| Interplus Group Limited | Construction | 2022 |
| Intervox UK Limited | Manufacturing | 2009 |
| Intrastat Europe Ltd | Extraterritorial | 2024 |
| Intuitive Business Consulting Limited | Professional & scientific | 2013 |
| Intuitive Business Solutions Limited | Information & communication | 2026 |
| Invenit Global Limited | Administrative & support | 2013 |
| Inventcons Ltd | Professional & scientific | 2020 |
| Investia Software Solutions Limited | Information & communication | 2005 |
| Invigorise Limited | Health & social care | 2017 |
| Invisible Inc. Limited | Extraterritorial | 1993 |
| Inviting Events Ltd | Professional & scientific | 2015 |
| Involved Solutions Ltd | Administrative & support | 2011 |
| IPO2 Limited | Professional & scientific | 2002 |
| Ippl Holdings Limited | Extraterritorial | 2011 |
| IPS Roofing Limited | Construction | 2012 |
| IPS Waterproofing Limited | Construction | 2025 |
| Ipso Opere Ltd | Health & social care | 2013 |
| IQ Clean Touch Services Limited | Administrative & support | 2025 |
| Iqoniq Limited | Professional & scientific | 2021 |
| Irbconsulting Ltd | Professional & scientific | 2026 |
| Iremi (UK) Ltd | Wholesale & retail | 2009 |
| Iron & Oak Group Limited | Professional & scientific | 2026 |
| Irvings Property Limited | Real estate | 2005 |
| Irvings Property Management (Catterick) Limited | Real estate | 2019 |
| Isabel Silver Limited | Hospitality | 2022 |
| Isabelle Lesser Psychotherapy Ltd | Health & social care | 2020 |
| Isbee Limited | Professional & scientific | 2005 |
| Isbjorn Ltd | Information & communication | 2011 |
| Isis Electronics Limited | Other services | 1995 |
| Islam TM Ltd | Construction | 2024 |
| IT IS What IT IS Film & TV Ltd | Information & communication | 2018 |
| IT Specialists KEW Limited | Other services | 2025 |
| IT Support World Limited | Information & communication | 2014 |
| Italian Quarter Productions Ltd | Arts & recreation | 2026 |
| ITH Consulting Limited | Administrative & support | 2011 |
| Itqan Arabic Content Ltd | Information & communication | 2022 |
| Itresq Limited | Information & communication | 2011 |
| ITS Cyber Smart Ltd | Other services | 2025 |
| Ivison's Country Store Limited | Wholesale & retail | 2015 |
| IVY Walls Trading Limited | Professional & scientific | 2017 |
| Iwmc 1 Limited | Construction | 2020 |
| Iyswim Limited | Professional & scientific | 2018 |
| IZ Assist UK CIC | Administrative & support | 2023 |
| IZM Limited | Administrative & support | 2003 |
| Izquierdo Limited | Hospitality | 2011 |
| Izzy Lane Limited | Manufacturing | 2006 |
| Izzy Rose Hair Limited | Other services | 2022 |
| J B Decor Ltd | Professional & scientific | 2025 |
| J D Howden Limited | Construction | 2012 |