| Idle Time Press UK Ltd | Wholesale & retail | 2022 |
| Iges UK Pharma Consulting Ltd. | Professional & scientific | 2019 |
| Ignite Management Solutions Ltd | Professional & scientific | 2015 |
| IHM Holdings Ltd | Financial services | 2025 |
| Ihope Limited | Hospitality | 2024 |
| ILIM1 Limited | Professional & scientific | 1971 |
| Illuminate.Tv Limited | Information & communication | 2016 |
| Image Revelation Limited | Professional & scientific | 2000 |
| Imagekings Limited | Information & communication | 2000 |
| Imfravis Flat 3 Limited | Real estate | 2024 |
| Imfravis Limited | Real estate | 1961 |
| Impactr Ltd | Professional & scientific | 2024 |
| Impresa Property Ltd | Real estate | 2020 |
| Impulse Fitness Clothing Ltd | Wholesale & retail | 2020 |
| IN Thyme Innovation Ltd | Professional & scientific | 2026 |
| In-House Wellbeing Ltd | Other services | 2026 |
| In-Tech Mobiles Limited | Information & communication | 2004 |
| In-Tech Telecom Holdings Limited | Information & communication | 2012 |
| In-Tech Telecom Limited | Information & communication | 2001 |
| Inbox Insight Group Limited | Financial services | 2016 |
| Inbox Insight Limited | Information & communication | 2010 |
| Inchcape Family Estates Limited | Professional & scientific | 2002 |
| Incisively Ltd | Professional & scientific | 2021 |
| Inclusion Genomics Ltd | Professional & scientific | 2021 |
| Independent Crop Data Limited | Extraterritorial | 2014 |
| Indge Services Ltd | Wholesale & retail | 2023 |
| India LEE Ltd | Arts & recreation | 2016 |
| Indigo DPM Limited | Transport & logistics | 2015 |
| Indigo Medical Limited | Health & social care | 2020 |
| Induction Recruitment Ltd | Administrative & support | 2020 |
| Infinity Operations Ltd | Financial services | 2024 |
| Infinity Playgrounds Ltd | Arts & recreation | 2023 |
| Influence Inc Ltd | Professional & scientific | 2012 |
| Inform Logistics Limited | Professional & scientific | 2008 |
| Ingenium Consultants Ltd | Professional & scientific | 2025 |
| Inmalo Holdings Ltd | Financial services | 2024 |
| Inner Line Consulting Ltd | Information & communication | 2025 |
| Innes Smith Interiors Ltd | Professional & scientific | 2025 |
| Innesco Ltd | Administrative & support | 2009 |
| Innotech Air Conditioning Control Systems Limited | Professional & scientific | 1992 |
| INNOV8-ING Limited | Construction | 2016 |
| Innovating Futures Ltd | Information & communication | 2017 |
| Innoveq Ltd | Professional & scientific | 2021 |
| Innslodge Publications Limited | Information & communication | 1974 |
| INOV8 Marketing Ltd | Administrative & support | 2017 |
| Inside Business Limited | Professional & scientific | 1993 |
| Insight (Southern) Limited | Wholesale & retail | 2001 |
| Insight Cleaning Supplies Ltd | Wholesale & retail | 2019 |
| Insight Haven Ltd | Professional & scientific | 2025 |
| Inspirascapes Limited | Administrative & support | 2020 |
| Inspirational Classrooms Limited | Extraterritorial | 2012 |
| Inspired Information Services Limited | Information & communication | 2010 |
| Inspired Lifestyle Spaces Ltd | Construction | 2024 |
| Intapsych Ltd. | Education | 2008 |
| Intech I.T. Solutions Limited | Information & communication | 2014 |
| Intech Property Limited | Real estate | 2025 |
| Integrated Construction Solutions Limited | Professional & scientific | 1998 |
| Integrated Marketing Matters Limited | Professional & scientific | 2002 |
| Intelligent Incite Limited | Information & communication | 2017 |
| Intelligent Ontologies Ltd | Professional & scientific | 2017 |
| Intense Fitness Limited | Arts & recreation | 2016 |
| Interior Design & Supply Limited | Other services | 2003 |
| Interiorbuild (UK) Limited | Construction | 2004 |
| Interlight Training Ltd | Information & communication | 2017 |
| Internascor Limited | Professional & scientific | 2016 |
| International Banking Consultancy Ltd | Professional & scientific | 2002 |
| International Business Machines Limited | Professional & scientific | 1995 |
| International Design UK Limited | Information & communication | 1998 |
| International Junior Miss UK Ltd | Professional & scientific | 2019 |
| International Market Management Ltd | Professional & scientific | 2012 |
| International Marketers (London) Limited | Construction | 1946 |
| Internet of Things Privacy Forum Ltd | Professional & scientific | 2015 |
| Intrafocus Limited | Professional & scientific | 2011 |
| Investgame Ltd | Information & communication | 2025 |
| Invictus Scaffolding Ltd | Construction | 2025 |
| Invictus Vape UK Limited | Wholesale & retail | 2019 |
| Invigor Life Ltd | Arts & recreation | 2020 |
| Invisible Edit Limited | Information & communication | 2011 |
| IOI Children & Family Professional Services Limited | Hospitality | 2022 |
| Ipera Coatings Limited | Professional & scientific | 2001 |
| Ipsden Estate Development Limited | Construction | 2018 |
| Iridium River Ltd | Health & social care | 2023 |
| IRM J Ltd | Construction | 2003 |
| IRM Models Limited | Information & communication | 2022 |
| Irma Holdings Ltd | Financial services | 2024 |
| Irma Management Limited | Manufacturing | 1959 |
| Ironband Limited | Real estate | 2011 |
| Ironside Financial Services Limited | Financial services | 2022 |
| Ironsides Rest Limited | Administrative & support | 1996 |
| Ironstead Ltd | Construction | 2025 |
| Ironwood Solutions Ltd | Information & communication | 2024 |
| Isaca Winchester Chapter Ltd | Other services | 2019 |
| Isalex Consulting Ltd | Information & communication | 2024 |
| Isambard Projects Limited | Information & communication | 1996 |
| Isfield Estate Ltd | Real estate | 2025 |
| Isla and Isma Limited | Health & social care | 2010 |
| Island Organics Limited | Wholesale & retail | 2014 |
| Istanbul Barber Thatcham Ltd | Other services | 2018 |
| Itchen Valley Property Limited | Real estate | 2015 |
| Ivan Stacey Recovery Limited | Transport & logistics | 1997 |