| IGS Aquafeed Ltd | Manufacturing | 2020 |
| Ilyash Ltd | Information & communication | 2023 |
| IM Solar Solutions Ltd | Construction | 2025 |
| IMA Property Essex Ltd | Real estate | 2021 |
| Imaje Aesthetics Ltd | Health & social care | 2025 |
| IMC Markets Ltd | Professional & scientific | 2023 |
| Immr Designs (UK) Limited | Information & communication | 2021 |
| Impact Ventures Worldwide Ltd | Other services | 2018 |
| Impala Films Ltd | Information & communication | 2022 |
| Imparando (UK) Limited | Information & communication | 2010 |
| Imperial Management (Westcliff) Limited | Households | 1998 |
| Imperial Nails Ltd | Other services | 2022 |
| Implementus Limited | Real estate | 2004 |
| Imtex Holdings Limited | Wholesale & retail | 2016 |
| IN ANY Event Catering Ltd | Hospitality | 2020 |
| IN Detail Automotive Detailing Ltd | Households | 2010 |
| IN DI Streets Restaurant Bar and Grill Ltd | Hospitality | 2025 |
| IN Steel Buildings Limited | Wholesale & retail | 2008 |
| Inception Cast Studio Ltd | Information & communication | 2024 |
| Inception INK Limited | Other services | 2022 |
| Incognito Solutions Limited | Administrative & support | 2015 |
| Indigo London Property Services Ltd | Construction | 2022 |
| Indur Solutions Limited | Information & communication | 2009 |
| Industrial Pipework Services Limited | Construction | 2006 |
| Industrial Revelation Limited | Information & communication | 2011 |
| Infinite Baffle Limited | Manufacturing | 1992 |
| Infinity Coats Ltd | Construction | 2018 |
| Infinity Direct Limited | Information & communication | 2001 |
| Infinity Financial Planning Limited | Financial services | 2010 |
| Infinity Roofing and Building Solutions Limited | Construction | 2011 |
| Ingrid's Ipass Limited | Construction | 2006 |
| Inhouse Office Coffee Co Limited | Hospitality | 2026 |
| Inkygreen Limited | Professional & scientific | 2009 |
| Inline Carpentry Ltd | Manufacturing | 2025 |
| Inna Health Limited | Health & social care | 2023 |
| Inner London Construction Limited | Construction | 2024 |
| Innovaro Technology Ltd | Wholesale & retail | 2020 |
| Innovate W3 Ltd | Professional & scientific | 2024 |
| Innovation PH Limited | Other services | 2008 |
| Innovative Agents Ltd | Wholesale & retail | 2025 |
| Innovative Electrical Services Ltd | Construction | 2017 |
| Innovative Steel Solutions Limited | Manufacturing | 2014 |
| Innovision Private Limited | Information & communication | 2024 |
| Innowave Systems Limited | Information & communication | 2024 |
| Inouran Limited | Wholesale & retail | 2024 |
| Inrs Consultancy Ltd | Information & communication | 2015 |
| Insert Coin Limited | Wholesale & retail | 2010 |
| Insight Creative Limited | Professional & scientific | 2021 |
| Inspired by Arctic Limited | Professional & scientific | 2017 |
| Inspired Kitchens Cambridge Limited | Wholesale & retail | 2026 |
| Insta-Waste Aggregates Ltd | Manufacturing | 2024 |
| Install Interiors Limited | Construction | 2015 |
| Insuremore Ltd | Financial services | 2016 |
| Integer Vehicle Solutions Ltd | Wholesale & retail | 2017 |
| Integrated Hydraulic Solutions UK Ltd | Administrative & support | 2015 |
| Integriguard Consultancy Ltd | Professional & scientific | 2025 |
| Integritas Consultancy Ltd | Professional & scientific | 2014 |
| Integrity Building Innovations Ltd | Construction | 2019 |
| Integrity Group UK Holdings Ltd | Financial services | 2026 |
| Integrity Travel Group (Holdings) Limited | Extraterritorial | 2008 |
| Integrity Travel Group Limited | Administrative & support | 1961 |
| Interact SLT Ltd | Health & social care | 2023 |
| Interactive Rights Management Limited | Administrative & support | 2004 |
| Interactive Training Aids Limited | Other services | 2014 |
| Intercity Communications Limited | Manufacturing | 1991 |
| Interior Design at Tinted Twig Ltd | Professional & scientific | 2024 |
| Interiors by Tracy Ritchie Ltd | Professional & scientific | 2024 |
| Internal Accounts Ltd | Administrative & support | 2023 |
| International Rescue Services Ltd | Construction | 2016 |
| Interruptive Marketing Solutions Ltd | Information & communication | 2022 |
| Intrepid Adventures Ltd | Arts & recreation | 2018 |
| Intuitive IT Ltd | Information & communication | 2024 |
| Intutainment Ltd | Arts & recreation | 2024 |
| Involved Community Projects Ltd | Households | 2021 |
| Invora Invest Ltd | Hospitality | 2025 |
| Ipharmacy Limited | Professional & scientific | 2000 |
| Irish Gulf Precast Ltd | Construction | 2023 |
| Irish Whiskey Glass Limited | Manufacturing | 2017 |
| Ironwood Carpentry Limited | Construction | 2025 |
| IRS Property Services Ltd | Real estate | 2025 |
| Irving Brown Limited | Real estate | 2021 |
| Isabelle Hefford Consulting Ltd | Professional & scientific | 2020 |
| Isec Group Services Limited | Administrative & support | 2025 |
| Isett Limited | Financial services | 2022 |
| Island Mode Limited | Construction | 2013 |
| Islandmangrupp Limited | Information & communication | 2018 |
| ISR Management Limited | Extraterritorial | 2014 |
| Istan Limited | Administrative & support | 2022 |
| ISW Accountancy Limited | Professional & scientific | 2007 |
| IT LOG Ltd | Other services | 2014 |
| IT Perspectives Limited | Administrative & support | 1997 |
| ITA Playwall Ltd | Manufacturing | 2018 |
| Itemedical Limited | Information & communication | 2022 |
| Itisaal Ltd | Information & communication | 2021 |
| Itpmc Ltd | Wholesale & retail | 2019 |
| IVY Ellis Socks Limited | Wholesale & retail | 2022 |
| IVY Fire Protection Ltd | Construction | 2024 |
| IVY Maintain & Develop Ltd | Construction | 2013 |
| Ixmat Limited | Information & communication | 2017 |
| IZB3 Limited | Health & social care | 2021 |