| Impact for Growth Ltd | Professional & scientific | 2025 |
| Impact Mental Health Peer Support Community Interest Company | Health & social care | 2013 |
| Imperium FM LLP | | 2011 |
| Impex Stock Ltd | Wholesale & retail | 2018 |
| Import Export Solutions Limited | Professional & scientific | 1998 |
| IMPORT4U Ltd | Wholesale & retail | 2013 |
| Impress Europe London Limited | Administrative & support | 2015 |
| Impulse Heating Limited | Construction | 2010 |
| Imran Sarwar Ltd | Information & communication | 2011 |
| IN Branding Limited | Professional & scientific | 2011 |
| IN Service of Art, NOT the EGO Ltd | Wholesale & retail | 2024 |
| In&Out Solutions Ltd | Administrative & support | 2010 |
| IN2GLOBAL Limited | Administrative & support | 2005 |
| Inaaya Express Limited | Transport & logistics | 2023 |
| Incite Assets Ltd | Financial services | 2022 |
| Incite Communications Limited | Professional & scientific | 2018 |
| Inclusive Healthcare Solutions Ltd | Health & social care | 2026 |
| Incy-Dent Ltd | Wholesale & retail | 2016 |
| IND Consultancy Limited | Transport & logistics | 2021 |
| Independent Mediators Ltd | Professional & scientific | 2007 |
| Indian Box Ltd | Hospitality | 2020 |
| Indigo Secretaries Limited | Administrative & support | 2000 |
| Indigo Supermarket Group Limited | Wholesale & retail | 2025 |
| Indispice Loughton Limited | Hospitality | 2024 |
| Indom Services Limited | Construction | 1995 |
| Inex Contracting Limited | Administrative & support | 2003 |
| Infinite Design Studio Ltd | Wholesale & retail | 2018 |
| Infinity Build Construct Limited | Construction | 2021 |
| Infinity Contractors Limited | Construction | 2018 |
| Infinity Haulage Ltd | Transport & logistics | 2025 |
| Infinity Protection Ltd | Financial services | 2020 |
| Infinityhealthandcareservices Limited | Health & social care | 2026 |
| Inflate Clubhouse Ltd | Arts & recreation | 2025 |
| Influential Marketing Ltd | Professional & scientific | 2004 |
| Influtik Ltd | Professional & scientific | 2024 |
| Infra-Construct Limited | Construction | 2023 |
| Infraserve Limited | Information & communication | 2024 |
| Ingram in Business Limited | Administrative & support | 2006 |
| Initex Consulting Ltd | Construction | 2025 |
| Initial Incentives Limited | Professional & scientific | 1987 |
| Innocent Fetishes Limited | Wholesale & retail | 2021 |
| INNOV8 Bathrooms and Heating Ltd | Construction | 2019 |
| Innova Lettings Limited | Real estate | 2016 |
| Innova Property Developments Limited | Construction | 2009 |
| Innovacare Services Ltd | Professional & scientific | 2025 |
| Innovatepath Consulting Limited | Education | 2024 |
| Innovating Multi Trading Ltd | Construction | 2015 |
| Innovations Consulting Ltd | Wholesale & retail | 2015 |
| Innovations Ventures Ltd | Wholesale & retail | 2020 |
| Insignia Outsource Limited | Administrative & support | 2019 |
| Insite Group Limited | Information & communication | 2018 |
| Insitu FM Ltd | Water & waste | 2014 |
| Insitu Site Testing Ltd | Construction | 2015 |
| Inspire Performing Arts Limited | Arts & recreation | 2025 |
| Inspired Painting Contractors Ltd | Construction | 2018 |
| Inspiring Developments Ltd | Construction | 2021 |
| Inspyria Limited | Real estate | 2024 |
| Insta Laundry Groups Limited | Other services | 2021 |
| Integra-Flame Ltd | Construction | 2021 |
| Integral Property Services (Luton) Limited | Construction | 2011 |
| Integrated Retail Limited | Professional & scientific | 2007 |
| Intelligent Platforms Technology Limited | Information & communication | 2021 |
| Intelligent Procurement Solutions Limited | Professional & scientific | 2004 |
| Intelligent Property Assets Limited | Construction | 2020 |
| Intellilearn Consulting Ltd | Education | 2023 |
| Interimsdirect.Com Limited | Administrative & support | 2004 |
| Internet Radio Ltd | Information & communication | 2019 |
| Interquick Delivery Services Limited | Transport & logistics | 2015 |
| Interstate Cars Limited | Administrative & support | 2018 |
| Invesco Capita Holdings Limited | Financial services | 2004 |
| ION Marinescu Ltd | Transport & logistics | 2025 |
| ION Pascal Construct Services Ltd | Construction | 2024 |
| Ionut Pletosu Construction Ltd | Construction | 2023 |
| IP TEC Solar Limited | Information & communication | 2021 |
| Ire-Stock Ltd | Wholesale & retail | 2022 |
| Irian Consulting Ltd | Professional & scientific | 2023 |
| Irmak Holdings Limited | Financial services | 2025 |
| Irmak Lounge Limited | Hospitality | 2020 |
| Irmak Patisserie Ltd | Wholesale & retail | 2025 |
| Irotarita Ltd | Construction | 2022 |
| IS Design Limited | Administrative & support | 2002 |
| ISA Luton Limited | Hospitality | 2018 |
| Isales Academy Limited | Education | 2017 |
| Ises Foods Limited | Manufacturing | 2025 |
| Island Imports Limited | Wholesale & retail | 2021 |
| Island Mart Limited | Wholesale & retail | 2023 |
| Island Shine Limited | Administrative & support | 2022 |
| Isotonik Studios Ltd | Information & communication | 2017 |
| IT PMO Ltd | Information & communication | 2025 |
| It-Soft Services Ltd | Wholesale & retail | 2016 |
| Italian Coffee Shop Limited | Hospitality | 2018 |
| Itarcus Ltd | Information & communication | 2024 |
| Itechno Support Limited | Information & communication | 2023 |
| Item Products Holdings Ltd | Financial services | 2012 |
| Iulandra Limited | Construction | 2015 |
| Ivory Function Suite Limited | Hospitality | 2017 |
| IZB Enterprises Ltd | Wholesale & retail | 2023 |
| J & C Accommodations Ltd | Real estate | 2023 |
| J & P Roofing and Cladding Limited | Construction | 2020 |
| J B Smith Construction Limited | Construction | 2011 |