| Instrument & Control Services Limited | Manufacturing | 1979 |
| Instrumentology Ltd | Administrative & support | 2026 |
| Insu-Flex Ltd | Manufacturing | 2018 |
| Insync Engineering Ltd | Professional & scientific | 2014 |
| Insync Sales Services Ltd | Professional & scientific | 2021 |
| Insync Solutions Limited | Information & communication | 2012 |
| INT32 Ltd | Information & communication | 2024 |
| Inta Education Ltd | Administrative & support | 2018 |
| Integer Investments Limited | Real estate | 1951 |
| INTEGR8Z Ltd | Information & communication | 2023 |
| Integra Academy Limited | Education | 2026 |
| Integra Asset Management Limited | Education | 2026 |
| Integra Care Homes Limited | Health & social care | 2007 |
| Integra Care Management Limited | Health & social care | 2004 |
| Integra Education Asset Management Limited | Education | 2026 |
| Integra Education Limited | Education | 2025 |
| Integra Education North Limited | Education | 2026 |
| Integra Education Recruitment Ltd | Administrative & support | 2016 |
| Integra Education South Limited | Education | 2026 |
| Integra Global Resourcing Limited | Education | 2026 |
| Integra Personnel Limited | Education | 2026 |
| Integra Recruitment Group Limited | Education | 2026 |
| Integra Site Services Limited | Professional & scientific | 2017 |
| Integra Tuition Limited | Education | 2026 |
| Integral Health Solutions Ltd | Professional & scientific | 2012 |
| Integral Tuition Limited | Administrative & support | 2024 |
| Integrated Biologix Ltd | Professional & scientific | 2024 |
| Integrated Manufacturing Services Ltd | Manufacturing | 2023 |
| Integrated Power Engineering Limited | Manufacturing | 2026 |
| Integrated Premium Care Ltd | Health & social care | 2025 |
| Integrity GAS, Plumbing and Heating Ltd | Construction | 2017 |
| Inteli Limited | Professional & scientific | 2012 |
| Intelligent Analytical Solutions Ltd | Professional & scientific | 2015 |
| Intelligent Business Sales Limited | Administrative & support | 2014 |
| Intelligent Home Information Limited | Information & communication | 2024 |
| Intelligent Questions Ltd | Professional & scientific | 2012 |
| Intelligent Sales Agencies Ltd | Wholesale & retail | 2022 |
| Intelligent Vehicle Management Limited | Professional & scientific | 2025 |
| Intelliscope Limited | Administrative & support | 2012 |
| Intelliweb Limited | Information & communication | 2021 |
| Intennis Limited | Information & communication | 2024 |
| Interaxis Machine Tools Services Ltd | Manufacturing | 2014 |
| Interaxis Machinery Services Ltd | Manufacturing | 2012 |
| Intercoastal Limited | Administrative & support | 2024 |
| Interconstruction Building Services Limited | Construction | 1997 |
| Interefurb Limited | Construction | 2017 |
| Interfactor Solutions Limited | Professional & scientific | 2020 |
| Interglobe Logistics Ltd | Transport & logistics | 2010 |
| Interior Door Systems Limited | Manufacturing | 1996 |
| Interjob Solutions Europe Limited | Professional & scientific | 2025 |
| Internal Control & Systems Security Limited | Information & communication | 2014 |
| Internal Plastering Services Ltd | Construction | 2024 |
| International Airport Concierge Ltd | Administrative & support | 2021 |
| International Forte Limited | Other services | 2017 |
| International Health Solutions Limited | Manufacturing | 2003 |
| International Leisure Brands (Logistics) Limited | Wholesale & retail | 2019 |
| International Leisure Brands Europe Limited | Professional & scientific | 2019 |
| International Leisure Brands Limited | Wholesale & retail | 2019 |
| International Leisure Group Limited | Financial services | 2018 |
| International Nuclear Services Limited | Professional & scientific | 1973 |
| International Piping Design Ltd | Professional & scientific | 2020 |
| International Reseguros Recoveries Limited | Financial services | 2021 |
| International Road Ferry Ltd | Transport & logistics | 2004 |
| International Thai Foundation Ltd | Education | 2010 |
| International Training & Qualifications Ltd | Education | 2025 |
| Interprocess Limited | Manufacturing | 2018 |
| Intext Renovation Restoration Limited | Construction | 2023 |
| Intilery.Com Ltd | Information & communication | 2012 |
| Intouch Accounting Limited | Professional & scientific | 2010 |
| Intrepid Software Solutions Ltd | Other services | 2018 |
| Intri-Care Homes Ltd | Health & social care | 2026 |
| Intri-Care Ltd | Health & social care | 2024 |
| Intrigue Digital Ltd | Information & communication | 2020 |
| Intrinsic Logic Solutions Limited | Professional & scientific | 2016 |
| Intro Construction Recruitment Limited | Administrative & support | 2023 |
| Invasystems UK Ltd. | Information & communication | 2009 |
| Invectra Limited | Professional & scientific | 2025 |
| Invek Surveys Limited | Professional & scientific | 1993 |
| Invenens Limited | Professional & scientific | 2014 |
| Invent and Invest | Professional & scientific | 2001 |
| Invent Energy Systems Ltd | Professional & scientific | 2012 |
| Inventive Outcomes Limited | Information & communication | 2015 |
| Inventya Capital Ltd | Financial services | 2025 |
| Inventya Holdings Limited | Financial services | 2015 |
| Inventya Ltd | Professional & scientific | 2010 |
| Investmani Limited | Financial services | 2025 |
| Invicta Private Limited | Real estate | 2023 |
| Invictus Accounting Limited | Professional & scientific | 2018 |
| Invincible INK Limited | Other services | 2020 |
| Invisalign at Home Ltd | Health & social care | 2021 |
| Involve Health Limited | Administrative & support | 2021 |
| IOC Safety Services Limited | Professional & scientific | 2011 |
| Iochre Consulting Limited | Professional & scientific | 2005 |
| Iochre Tension Structures Ltd | Construction | 2006 |
| Ionic Community Connections Limited | Administrative & support | 2010 |
| Ionic Consulting Limited | Administrative & support | 2012 |
| Ionic Recruitment Group Limited | Administrative & support | 2020 |
| Ionic Recruitment Limited | Administrative & support | 2007 |
| Ionic Trades Limited | Administrative & support | 2016 |
| Ionio Limited | Information & communication | 2020 |