| Ishnights Limited | Real estate | 2024 |
| Ishtar Investments Ltd | Real estate | 2021 |
| ISI Property Management Ltd | Real estate | 2019 |
| ISI Trans Ltd | Transport & logistics | 2025 |
| Iskan Homes Ltd | Real estate | 2025 |
| Iskender 1 Ltd | Extraterritorial | 2021 |
| Iskender Birmingham Ltd | Extraterritorial | 2022 |
| Iskender Kebab Ltd | Hospitality | 2018 |
| ISL Skip Hire Limited | Water & waste | 2010 |
| Islabear Build Ltd | Construction | 2023 |
| Islam Brothers Ltd | Hospitality | 2016 |
| Islamic Art & Gifts. Ltd | Wholesale & retail | 2025 |
| Islamic Centre of London Ltd | Other services | 2017 |
| Islamic Clothing Ltd | Wholesale & retail | 2023 |
| Islamic College Ltd | Education | 2013 |
| Islamic Education Supplies Ltd | Manufacturing | 2026 |
| Islamic Family Services Ltd | Other services | 2026 |
| Islamic Law Board Ltd | Education | 2021 |
| Islamic Presentation Centre International Limited | Health & social care | 1990 |
| Islamic Relief Clothing Collections Ltd. | Water & waste | 2011 |
| Islamic Relief Worldwide | Health & social care | 1989 |
| Islamic Vision Limited | Wholesale & retail | 1990 |
| Islamophobia Awareness Month (IAM) Ltd | Other services | 2023 |
| Island Barn Aggregates Limited | Mining & quarrying | 1980 |
| Island Bites Catering Ltd | Hospitality | 2023 |
| Island Bridal Limited | Wholesale & retail | 2022 |
| Island Close (Freehold) Limited | Real estate | 2009 |
| Island Commerce LP | | 2017 |
| Island Delight Limited | Professional & scientific | 1997 |
| Island Intergroup LP | | 2017 |
| Island LOO Limited | Wholesale & retail | 2026 |
| Island Meals Limited | Wholesale & retail | 2022 |
| Island Patties Limited | Wholesale & retail | 2022 |
| Island Sea Supermarket Ltd | Wholesale & retail | 2022 |
| Island Spice Caribbean Takeaway Limited | Hospitality | 2015 |
| Islaw Limited | Wholesale & retail | 2021 |
| Isle Events Limited | Professional & scientific | 2017 |
| Isle Group Limited | Professional & scientific | 2015 |
| Isle of Wight Aggregates Limited | Wholesale & retail | 2002 |
| Isle Utilities Limited | Professional & scientific | 2010 |
| Islimi Arts Ltd | Wholesale & retail | 2019 |
| Islington Gates Management Company Limited | Households | 2003 |
| Islow Ltd | Information & communication | 2023 |
| Islsps Limited | Wholesale & retail | 2020 |
| ISM Services Ltd | Health & social care | 2021 |
| Ismaeel Group Limited | Professional & scientific | 2025 |
| Ismaeel Halal Ltd | Wholesale & retail | 2018 |
| Ismaeil MO Solutions Ltd | Transport & logistics | 2025 |
| Ismah Property Management Limited | Real estate | 2019 |
| Ismah Property Solutions Limited | Real estate | 2026 |
| ISMAHA123456 Limited | Health & social care | 2023 |
| Ismail Enterprises Ltd | Real estate | 2019 |
| Ismail Optometry Services Ltd | Health & social care | 2025 |
| Ismail Travel Limited | Transport & logistics | 2022 |
| Ismart Control Limited | Professional & scientific | 2019 |
| Ismart Design and Build Limited | Construction | 2025 |
| Ismart Holdings Ltd | Financial services | 2024 |
| Ismart Retail Limited | Wholesale & retail | 2022 |
| Isme Holdings Limited | Professional & scientific | 2008 |
| ISN Properties Limited | Real estate | 2019 |
| ISO Consultants U.K. Limited | Professional & scientific | 2017 |
| ISO Service Limited | Administrative & support | 2014 |
| ISO Sushi Limited | Hospitality | 2013 |
| Isochem Limited | Wholesale & retail | 1995 |
| Isola Bella Estate Limited | Real estate | 2023 |
| Isola Bella Limited | Wholesale & retail | 2017 |
| Isometra Consulting Limited | Professional & scientific | 2026 |
| Isonographer Limited | Health & social care | 2024 |
| Isonomy Education Ltd | Professional & scientific | 2013 |
| Isons Properties Ltd | Real estate | 2024 |
| Isoplexis Corporation UK Limited | Professional & scientific | 2018 |
| Isparx Security Solutions Ltd | Construction | 2016 |
| Ispu UK Ltd | Transport & logistics | 2017 |
| ISR Management Consultant Ltd | Education | 2024 |
| ISR Travel & Tourism Ltd | Administrative & support | 2026 |
| Isra Daycare Ltd | Education | 2010 |
| Isra Daycare Nursery Ltd | Health & social care | 2011 |
| Israelite School of Universal Practical Knowledge United Kingdom Ltd | Other services | 2021 |
| Israr.Dent Ltd | Health & social care | 2019 |
| ISS Connect Ltd | Wholesale & retail | 2026 |
| ISS Consultancy Ltd | Information & communication | 2013 |
| Issd Limited | Hospitality | 2026 |
| Issitt Limited | Hospitality | 2025 |
| Isskhan UK Ltd | Wholesale & retail | 2025 |
| Issy Delivery Limited | Transport & logistics | 2025 |
| Issy Property Ltd | Real estate | 2020 |
| IST Response Logistics Ltd | Wholesale & retail | 2017 |
| Istanbul Fashion DR Ltd | Wholesale & retail | 2024 |
| Istanbul Sheldon Ltd | Hospitality | 2023 |
| Istanbul Sheldon MH Ltd | Hospitality | 2025 |
| Istanbul Store Ltd | Wholesale & retail | 2023 |
| Istay Aparthotels Ltd | Real estate | 2022 |
| Istay Inn Ltd | Real estate | 2022 |
| Istay Residents Ltd | Construction | 2023 |
| Istay Studios Ltd | Construction | 2022 |
| Istds Ltd | Information & communication | 2013 |
| Istiqamah Madrasah Limited | Education | 2025 |
| Istreet Distribution Limited | Wholesale & retail | 2021 |
| Istudyonbail Limited | Hospitality | 2019 |
| Istudyonline Limited | Information & communication | 2017 |