| In-Sync Credit Services Limited | Financial services | 2012 |
| In-Sync Digital Limited | Professional & scientific | 2017 |
| In-Sync Factoring Limited | Administrative & support | 2018 |
| In-Sync Group Limited | Information & communication | 2011 |
| In-Sync Outsourcing Ltd | Professional & scientific | 2015 |
| In-Sync Tax LLP | | 2009 |
| IN2CROSSFIT Limited | Arts & recreation | 2011 |
| Inclusive Minds Collective CIC | Information & communication | 2020 |
| Incress Limited | Professional & scientific | 2006 |
| Incyp Logistics Limited | Transport & logistics | 2025 |
| Indigo Edge Ltd | Professional & scientific | 2026 |
| Industry Innovation Ltd | Information & communication | 2020 |
| Inetic Limited | Manufacturing | 2001 |
| Infinity Roofing & Construction Ltd | Construction | 2013 |
| Infinity Sports Academy Ltd | Arts & recreation | 2025 |
| Informatic Component Technology Limited | Manufacturing | 1991 |
| Infosirius Ltd | Information & communication | 2010 |
| Inghams Tax and Accounting Limited | Professional & scientific | 2015 |
| Ingsgar Limited | Real estate | 2020 |
| Ingwe Consulting Limited | Information & communication | 2024 |
| Initram Management Limited | Real estate | 2000 |
| INK Networks Limited | Information & communication | 2016 |
| Inkulumali Limited | Real estate | 2022 |
| Innofusion Limited | Wholesale & retail | 2024 |
| Innovate and Change Limited | Professional & scientific | 2020 |
| Innovate Biopharma Consulting Limited | Professional & scientific | 2020 |
| Innovera Technology Group Limited | Information & communication | 2026 |
| Innovision Landscapes Limited | Administrative & support | 2018 |
| INP Media Limited | Information & communication | 2003 |
| Insidevue Limited | Health & social care | 2007 |
| Insight AIE Ltd | Professional & scientific | 2020 |
| Inspectors-On-Line Limited | Administrative & support | 2000 |
| Inspiration Coaching & Development Limited | Professional & scientific | 2006 |
| Inspiring Workplaces Limited | Administrative & support | 2018 |
| Instate Fitness Cobham Limited | Arts & recreation | 2014 |
| Instate Fitness Group Limited | Administrative & support | 2014 |
| Instate Fitness Wandsworth Limited | Arts & recreation | 2021 |
| Instinctively Real Media Ltd | Professional & scientific | 2020 |
| Instructional Design and Training Limited | Administrative & support | 2023 |
| Integrahealth Solutions Ltd | Professional & scientific | 2024 |
| Integral Heating Limited | Construction | 2024 |
| Integrated Governance Solutions (IGS) Limited | Professional & scientific | 2016 |
| Integrium Advisors Limited | Other services | 2019 |
| Integrium Investments Limited | Financial services | 2025 |
| Intellectricals Ltd | Construction | 2017 |
| Intellidex Holdings Limited | Professional & scientific | 2021 |
| Interchange Back Office Limited | Administrative & support | 2021 |
| Interchange Interactive Ltd | Administrative & support | 2001 |
| Interchange Properties Limited | Real estate | 2021 |
| Intercultural Success Limited | Professional & scientific | 2006 |
| Interforum UK Limited | Professional & scientific | 1995 |
| Interim CFO Ltd | Professional & scientific | 2007 |
| International Advisory Services Limited | Professional & scientific | 2026 |
| International Well Integrity Ltd | Other services | 2019 |
| Interscape (UK) Limited | Wholesale & retail | 2012 |
| Intoss Limited | Manufacturing | 1987 |
| Intox Ltd | Manufacturing | 2023 |
| Intraserve Limited | Transport & logistics | 2014 |
| Intrepid FOX Consulting Limited | Professional & scientific | 2021 |
| Introtech Limited | Construction | 2006 |
| Inttec Solutions Limited | Information & communication | 2016 |
| Inuvu Limited | Professional & scientific | 2015 |
| Inventiva Limited | Information & communication | 2012 |
| Inventory Control Management Limited | Wholesale & retail | 2003 |
| Invermarkie Limited | Administrative & support | 2024 |
| Inverse Quanta Ltd | Professional & scientific | 2012 |
| Inverter Drives Southern Limited | Wholesale & retail | 2007 |
| Investment 89 Limited | Real estate | 2024 |
| Investnest Properties Limited | Real estate | 2024 |
| Invictus Management Limited | Professional & scientific | 2010 |
| Invoka Consulting Limited | Information & communication | 2022 |
| Inwood Forestry Ltd | Agriculture & fishing | 2020 |
| IPA Purchasing Limited | Wholesale & retail | 2001 |
| IPA Supplies Ltd | Wholesale & retail | 2013 |
| Ipsley Lodge Management Company Limited | Households | 1983 |
| Iq-Av Limited | Information & communication | 2017 |
| Irightmove Ltd | Information & communication | 2015 |
| Iris Landscapes Ltd | Administrative & support | 2025 |
| Iroko Construction Ltd | Construction | 2016 |
| Iron Gate Trading Ltd | Wholesale & retail | 2025 |
| Ironing & Cleaning Agency Ltd | Administrative & support | 2012 |
| Irving Brand Development Ltd | Professional & scientific | 2015 |
| Iscry Data Analysis Ltd | Information & communication | 2013 |
| Iski Holidays Limited | Administrative & support | 2014 |
| Island Kings Limited | Real estate | 2014 |
| Islands of the Pacific Limited | Information & communication | 2019 |
| Isnen Limited | Health & social care | 2014 |
| IST Scientific LLP | | 2015 |
| IT Remarket Limited | Water & waste | 2026 |
| IT Tailored Limited | Information & communication | 2007 |
| IT Webnet Support Ltd | Information & communication | 2014 |
| It's a Miracle! Ltd | Professional & scientific | 2026 |
| IT4FUN Ltd | Information & communication | 2016 |
| Itasca Technical Services Limited | Manufacturing | 2025 |
| Iter Limited | Professional & scientific | 2017 |
| Itergen Systems Ltd | Wholesale & retail | 2022 |
| ITR Global Limited | Water & waste | 2008 |
| ITW3 Limited | Information & communication | 2007 |
| Ivett Design and Build Ltd | Construction | 2018 |
| Ivory Gate Property Holdings Limited | Real estate | 2026 |