| IBJ Consulting Limited | Health & social care | 2020 |
| Ibox Services Ltd | Professional & scientific | 2025 |
| IC Innovate Limited | Information & communication | 2011 |
| Ic-Rad Ltd | Health & social care | 2020 |
| Icdans Limited | Education | 2017 |
| Ice Broken Productions Limited | Information & communication | 2020 |
| Ice Mauve Ltd | Health & social care | 2025 |
| Ice Projects Limited | Construction | 2013 |
| Ice Red Ltd. | Real estate | 2020 |
| Icecam Ltd | Manufacturing | 2025 |
| Icefog Industrial and Trading Co., Ltd. | Extraterritorial | 2013 |
| Iceni Portfolio Limited | Financial services | 2021 |
| Iceni Reserve Ltd | Professional & scientific | 2023 |
| Ichiban Property Ltd | Real estate | 2016 |
| Iconal Technology Ltd. | Professional & scientific | 2006 |
| ICS Computer Services Limited | Information & communication | 1987 |
| ID Food Solutions Ltd | Professional & scientific | 2015 |
| ID IT Services Ltd | Administrative & support | 2017 |
| ID Techex Limited | Information & communication | 1999 |
| IDB Bookkeeping Services Ltd | Professional & scientific | 2021 |
| Idea OWL Technologies Ltd | Information & communication | 2024 |
| Ideal Sante Ltd | Health & social care | 2025 |
| Ideal-Careerbridge (UK) Limited | Administrative & support | 2023 |
| Idealistic Financial Services Ltd | Financial services | 2015 |
| Idealistic Mortgage Services Ltd | Financial services | 2021 |
| Ideation Consulting Ltd | Professional & scientific | 2020 |
| Idee Homelife Manufacturing Co., Ltd. | Extraterritorial | 2021 |
| Identifind Ltd | Professional & scientific | 2016 |
| Identifont Limited | Extraterritorial | 2018 |
| Identifymobile Limited | Information & communication | 2014 |
| Identity Creative Limited | Professional & scientific | 2013 |
| IDF Clean Exteriors Ltd | Administrative & support | 2021 |
| Idie & Co Tech Advisory Limited | Information & communication | 2026 |
| Idina Limited | Financial services | 2016 |
| IDM Automotive Ltd | Manufacturing | 2025 |
| IDM Property Consulting Ltd | Real estate | 2019 |
| Idmd Properties Ltd | Real estate | 2021 |
| Idportal Limited | Information & communication | 2009 |
| Idyl Consulting Limited | Professional & scientific | 2018 |
| Iecp Investment Ltd | Financial services | 2024 |
| Ieso Digital Health (UK) Limited | Administrative & support | 2016 |
| Ieso Digital Health Limited | Health & social care | 2000 |
| IFD Consulting Limited | Professional & scientific | 2009 |
| IFM Europe Limited | Information & communication | 2002 |
| IFS Limited | Financial services | 1969 |
| Ifun Global Ltd | Information & communication | 2023 |
| Igallc Ltd | Mining & quarrying | 2022 |
| Igennus Limited | Professional & scientific | 2003 |
| Igentics Ltd | Information & communication | 2001 |
| Igentus Limited | Information & communication | 2024 |
| Igenxt Ltd | Professional & scientific | 2024 |
| Igirisu Joba Club Ltd | Arts & recreation | 2018 |
| Iglone Limited | Professional & scientific | 2026 |
| IGM Environmental Ltd | Hospitality | 2003 |
| Igne Limited | Manufacturing | 2013 |
| Ignite Digital Media Ltd | Information & communication | 2025 |
| Ignite Performance Ltd | Education | 2019 |
| Ignitebio Consulting Ltd | Professional & scientific | 2025 |
| Ignition Sports Ltd | Arts & recreation | 2025 |
| Ignota Group Limited | Professional & scientific | 2026 |
| Ignota Labs Limited | Professional & scientific | 2021 |
| Iguana Investments Ltd | Financial services | 2019 |
| Ihaa International Services Ltd | Other services | 2021 |
| IHT International Hardware Limited | Extraterritorial | 2011 |
| Iinflo Design Ltd | Information & communication | 2025 |
| Iion Ltd | Manufacturing | 2026 |
| Iissee Ltd | Wholesale & retail | 2024 |
| IJ Motors Limited | Wholesale & retail | 2025 |
| Ijab Ltd | Health & social care | 1998 |
| IJC Events Limited | Administrative & support | 2025 |
| IJC Holdings Limited | Financial services | 2016 |
| IJM Air Conditioning & Refrigeration Ltd | Construction | 2014 |
| Ikart Limited | Wholesale & retail | 2020 |
| Ikee Real Estate (UK) Ltd | Extraterritorial | 2023 |
| Ikel Ltd | Manufacturing | 2017 |
| Ikona Logistics Ltd | Professional & scientific | 2026 |
| IL Barbiere Ltd | Other services | 2008 |
| IL Botticelli Limited | Manufacturing | 2024 |
| IL Sapore Ltd | Hospitality | 2025 |
| Ilagosa and Company Limited | Health & social care | 2014 |
| Ileana Compozite Ltd | Manufacturing | 2023 |
| Ilexir Holdings Limited | Financial services | 2015 |
| Ilgaz Group Ltd | Wholesale & retail | 2023 |
| Ilie Cristinel Ltd | Manufacturing | 2022 |
| Iliffe Media Group Limited | Financial services | 2018 |
| Iliffe Media Limited | Information & communication | 2016 |
| Iliffe Media Publishing Limited | Information & communication | 2016 |
| Iliffe Print Cambridge Limited | Manufacturing | 1929 |
| Iliomad Health Data UK Limited | Professional & scientific | 2023 |
| Illumibook Publishing Limited | Information & communication | 2024 |
| Illumina Cambridge Limited | Professional & scientific | 1998 |
| Illumina Ventures Labs Ltd | Professional & scientific | 2023 |
| IMA Cleaning Limited | Administrative & support | 2025 |
| IMA Sports & Culture Limited | Professional & scientific | 2026 |
| Image Ability Ltd. | Professional & scientific | 2020 |
| Imaghine Resources UK Limited | Water & waste | 2026 |
| Imaginary PUB the Bell Balsham Ltd | Hospitality | 2025 |
| Imaginated Pursuits Limited | Information & communication | 2023 |
| Imaging Reports Limited | Health & social care | 2017 |
| Imago Cambridge Ltd | Hospitality | 2011 |