| Insight Forward Ltd | Professional & scientific | 2023 |
| Insightsmed Consultants Ltd | Extraterritorial | 2024 |
| Inspired Expressions Ltd | Health & social care | 2025 |
| Insurance Services 4 U Ltd | Real estate | 2004 |
| Insurtech Gateway Limited | Financial services | 2016 |
| Intangiable Limited | Professional & scientific | 2022 |
| Intangiable SR One II Nominees Ltd | Financial services | 2022 |
| Intasect Design Ltd | Professional & scientific | 2026 |
| Integral Automation Ltd | Professional & scientific | 2018 |
| Integrated Lifestyle Ltd | Professional & scientific | 2018 |
| Integrated Protection Maintenance Services Limited | Administrative & support | 2012 |
| Integrity Personnel Limited | Administrative & support | 1999 |
| Intellibotic Solutions Limited | Information & communication | 2025 |
| Intelligent Auto Services Ltd | Wholesale & retail | 2012 |
| Intelligent Wealth Lifetime Partners Limited | Extraterritorial | 2019 |
| Intelliqa Limited | Information & communication | 2011 |
| Intellium Dinamics Ltd | Information & communication | 2023 |
| Intent Boxing Academy CIC | Arts & recreation | 2025 |
| Intent Boxing Ltd | Arts & recreation | 2024 |
| Intent Fitness Ltd | Arts & recreation | 2021 |
| Intercede Aviation Limited | Professional & scientific | 2008 |
| Intermode Shipping Ltd | Transport & logistics | 2003 |
| Internal Compass Ltd | Health & social care | 2025 |
| International Artisan Vinegars Limited | Manufacturing | 2025 |
| International Assistance Ltd | Health & social care | 2021 |
| International College of Professional Management Limited | Administrative & support | 2019 |
| International Consultancy Europe Limited | Professional & scientific | 1997 |
| International Fundraising Consultancy Limited | Professional & scientific | 1999 |
| International Industrial Metals Limited | Administrative & support | 2014 |
| International Partners Limited | Extraterritorial | 2000 |
| International Test Equipment Distributors Limited | Other services | 2023 |
| International Ultrasound Services Limited | Health & social care | 2016 |
| Intertype Studio Limited | Professional & scientific | 2020 |
| Intuity Consulting Limited | Professional & scientific | 2014 |
| Intuity Limited | Professional & scientific | 2014 |
| Investment Pension Solutions Limited | Financial services | 2009 |
| Investment Properties (Luton) Limited | Real estate | 1948 |
| Invicta IT Ltd | Information & communication | 2002 |
| Invictus Property Group Ltd | Real estate | 2023 |
| Invoke Finance Ltd | Financial services | 2017 |
| Inwood 23 Limited | Professional & scientific | 2022 |
| Inzodiac Ltd | Information & communication | 2020 |
| Iorro Limited | Administrative & support | 2018 |
| IP Tilsworth Ltd | Construction | 2020 |
| Ipac Global Ltd | Other services | 2020 |
| Ipdecorators.Tr Ltd | Construction | 2022 |
| IQ Technology Projects Ltd | Information & communication | 2020 |
| Iqon Investments International Limited | Real estate | 2023 |
| Iqteck Limited | Wholesale & retail | 2023 |
| IRF Communications Ltd | Information & communication | 2016 |
| Iris Gardening Services Limited | Administrative & support | 1994 |
| Ironclad Investment (UK) Ltd | Real estate | 2025 |
| Irrational Productions Limited | Extraterritorial | 2020 |
| Irwin Cine Ltd | Professional & scientific | 2021 |
| Irwings Ltd | Education | 2021 |
| Isa-Cam Ltd | Administrative & support | 2018 |
| Isaac Kenyon Limited | Professional & scientific | 2022 |
| Isaintjames Ltd | Information & communication | 2026 |
| Ishot Ltd | Construction | 2024 |
| Isitt Anaesthesia Ltd | Health & social care | 2012 |
| Iskha Ltd | Real estate | 2019 |
| Ismlark Limited | Construction | 2026 |
| Isoco(Uk) Ltd | Information & communication | 2013 |
| Isola Bella (Golders Green) Limited | Hospitality | 2010 |
| Isopol Consulting Limited | Information & communication | 2018 |
| Issa Construct Ltd | Construction | 2019 |
| Istac Health Limited | Health & social care | 2011 |
| Istidama Limited | Manufacturing | 2007 |
| IT Avenue Ltd | Information & communication | 2025 |
| IT Infrastructure Services Ltd | Information & communication | 2007 |
| IT Procure Limited | Information & communication | 2013 |
| IT Property Link Limited | Real estate | 2018 |
| IT Support Hub Limited | Administrative & support | 2023 |
| IT Training & Support Limited | Education | 2016 |
| It's Brand Inspired Limited | Professional & scientific | 2008 |
| It's Virtual Freedom Ltd | Information & communication | 2022 |
| Itality Catering Limited | Manufacturing | 2021 |
| Itchy Paws Ltd | Wholesale & retail | 2022 |
| Iteso Ltd | Hospitality | 2014 |
| ITS Active IT Limited | Information & communication | 2014 |
| IV Taxi Limited | Transport & logistics | 2021 |
| Ivey Financial Planning Ltd | Financial services | 2025 |
| Ivyring Property Limited | Real estate | 1992 |
| Izzi Renovations Ltd | Construction | 2020 |
| J & Drewz Limited | Real estate | 2022 |
| J & S Housing Group Ltd | Construction | 2026 |
| J & TJ Witterick LLP | | 2012 |
| J D Gregory House & Garden Ltd | Construction | 2024 |
| J Fenton & SON Ltd | Construction | 2022 |
| J J Murray Services Limited | Construction | 2011 |
| J M Potts Ltd | Construction | 2018 |
| J Mckinnie Electrical Limited | Construction | 2018 |
| J Morris Garden Services Limited | Construction | 2014 |
| J P Blunden Limited | Real estate | 2006 |
| J Ponce DE León Ltd | Professional & scientific | 2024 |
| J R M P Properties Limited | Real estate | 1968 |
| J R M P Rickmansworth Limited | Real estate | 2016 |
| J Robert Auto Cars Ltd | Wholesale & retail | 2025 |
| J Robinson Limited | Administrative & support | 2011 |
| J W Salmon Arboricultural Ltd | Administrative & support | 2009 |