| Inter M.K. Limited | Construction | 1999 |
| Inter-Action (Milton Keynes) Limited | Arts & recreation | 1975 |
| Interact Acclaim Limited | Extraterritorial | 2012 |
| Interact Consulting Limited | Administrative & support | 2006 |
| Interact Medical Group Holdings Ltd | Financial services | 2023 |
| Interact Medical Limited | Administrative & support | 1995 |
| Interact Medical Nursing Limited | Extraterritorial | 2015 |
| Interact Nursing Limited | Extraterritorial | 2015 |
| Interactive Data Systems Limited | | 1980 |
| Interactive Installs Limited | Manufacturing | 2011 |
| Interactive Online Commerce Limited | Professional & scientific | 2008 |
| Interbright Limited | Health & social care | 2016 |
| Intercargo Limited | Transport & logistics | 2006 |
| Intercom Software UK Limited | Information & communication | 2017 |
| Interfacing Limited | Professional & scientific | 1991 |
| Interform Holdings Limited | Information & communication | 2015 |
| Interim Logistics Consultancy Limited | Professional & scientific | 2024 |
| Interlogix Consulting Ltd | Information & communication | 2011 |
| International Car Rental Limited | Administrative & support | 1935 |
| International Client Solutions Ltd | Professional & scientific | 2018 |
| International Corporate Art Limited | Professional & scientific | 2000 |
| International Creative Works Limited | Wholesale & retail | 2023 |
| International Crisis Management Association Limited | Administrative & support | 2008 |
| International Dance Shoes Limited | Manufacturing | 1981 |
| International Flexible Packaging Agencies Ltd | Administrative & support | 2011 |
| International Food Store (Yorkshire) Limited | Wholesale & retail | 2022 |
| International Freight Connection Limited | Transport & logistics | 2003 |
| International House Real Estate Projects Management Limited | Real estate | 2017 |
| International Machinery Company Limited | Administrative & support | 1990 |
| International Maintenance Associate (IMA) Limited | Manufacturing | 2016 |
| International Maintenance Chemicals Ltd | Manufacturing | 1986 |
| International Merchants Limited | Wholesale & retail | 2019 |
| International Neuro Restoration Enablement Services Ltd | Health & social care | 2022 |
| International Recruiting Limited | Administrative & support | 2024 |
| International Spinal Cord Society | Administrative & support | 1997 |
| International Sports Fotos Limited | Professional & scientific | 2014 |
| International Technical Automotive Systems Ltd | Administrative & support | 2002 |
| International Technology Products (UK) Limited | Wholesale & retail | 1997 |
| International Waste Management Ltd | Administrative & support | 2004 |
| Internet and Sons Limited | Information & communication | 2018 |
| Internet Society UK Limited | Information & communication | 2017 |
| Internos Ltd | Administrative & support | 2026 |
| Intersource Medical Services Ltd | Health & social care | 2012 |
| Interstarlight Ltd | Information & communication | 2024 |
| Intervet UK Production Limited | Manufacturing | 1996 |
| Intervoxa Ltd | Administrative & support | 2026 |
| Intetrade Limited | Wholesale & retail | 2005 |
| Intex Facades Limited | Construction | 2004 |
| Intexion Limited | Construction | 2009 |
| Intility Ltd | Information & communication | 2017 |
| Intligentli Ltd | Information & communication | 2025 |
| Into Care Limited | Health & social care | 2022 |
| Intrade Copiers Limited | Administrative & support | 2019 |
| Intricall Group Limited | Financial services | 2026 |
| Intricall Ltd | Information & communication | 2019 |
| Introclean Limited | Administrative & support | 2020 |
| Introducing Business Ltd | Professional & scientific | 2025 |
| Intrust Living Limited | Administrative & support | 2012 |
| Intu Technologies Ltd | Information & communication | 2020 |
| Intune Properties Limited | Real estate | 2023 |
| Intw Media Ltd | Information & communication | 2024 |
| Intyre Productions Limited | Administrative & support | 2009 |
| INV3STMENTS Ltd | Real estate | 2025 |
| Invek Engineering Ltd | Manufacturing | 2016 |
| Inventum Technologies Ltd | Information & communication | 2025 |
| Inveritech UK Limited | Professional & scientific | 2022 |
| Invertivet Bearded Vets Ltd | Professional & scientific | 2022 |
| Invesco Enterprise Limited | Real estate | 2017 |
| Invesis UK Limited | Construction | 2001 |
| Invest Agility Solutions Ltd | Information & communication | 2019 |
| Invest S.R Limited | Administrative & support | 2020 |
| Investment & Management Consultancy Limited | Professional & scientific | 2015 |
| Investment Acquisition Trust Limited | Real estate | 1936 |
| Investment Matchmakers Ltd | Administrative & support | 2024 |
| Investment Space Limited | Real estate | 2021 |
| Investment Street Commercial Ltd | Real estate | 2025 |
| Investment Street Developments Ltd | Construction | 2018 |
| Investment Street Ltd | Real estate | 2013 |
| Investorwise Limited | Real estate | 2017 |
| Investrealm Limited | Construction | 1994 |
| Invictus Consultancy Services Limited | Administrative & support | 2011 |
| Invisible Journeys Limited | Professional & scientific | 2025 |
| Invoke Recruitment Limited | Professional & scientific | 2015 |
| Invotec Solutions Limited | Wholesale & retail | 2005 |
| Ioan Falati Ltd | Water & waste | 2020 |
| Ioan Plumbing Ltd | Construction | 2022 |
| IOE Osunde Ltd | Health & social care | 2023 |
| Iomega Solutions Ltd | Information & communication | 2020 |
| ION Kitchens Ltd | Construction | 2025 |
| ION Logistics Ltd | Transport & logistics | 2018 |
| Ion-X Ltd | Information & communication | 2017 |
| Ionel Pirvu Ltd | Administrative & support | 2025 |
| Ionic Recovery Limited | Professional & scientific | 2018 |
| Ionik Partners Ltd | Health & social care | 2026 |
| Ionut&Andreea Ltd | Transport & logistics | 2015 |
| Iortho Holdings Limited | Hospitality | 2025 |
| Iorys Ltd | Information & communication | 2019 |
| IOT Connectivity Limited | Information & communication | 2023 |
| IP 2 IP Networks Limited | Information & communication | 2024 |
| IPB Search Ltd | Extraterritorial | 2020 |