| Intelligent Textiles Group Limited | Financial services | 2020 |
| Intelligent Textiles Limited | Professional & scientific | 2002 |
| Intellijet Limited | Information & communication | 2012 |
| Intellikds Ltd | Professional & scientific | 2011 |
| Intellisurvey Limited | Information & communication | 2018 |
| Intellitek Limited | Information & communication | 2012 |
| Intense Physio Limited | Health & social care | 2021 |
| Intentional Care and Support Limited | Health & social care | 2025 |
| Inter Rail Services Ltd | Construction | 2024 |
| Inter-Gt Courier Ltd | Transport & logistics | 2019 |
| Interbar Limited | Construction | 1986 |
| Intercept Fire and Security Limited | Public administration | 2015 |
| Intercom Tech Ltd | Financial services | 2022 |
| Interim and Outsource Limited | Professional & scientific | 2003 |
| Interim Corporate Finance Limited | Professional & scientific | 2021 |
| Interlegal Partners Limited | Professional & scientific | 2025 |
| Interlist Ltd | Information & communication | 2014 |
| Interlive Media Ltd | Wholesale & retail | 2023 |
| Intermarble Ltd | Manufacturing | 2016 |
| International Craft(Wholesale) Limited | Wholesale & retail | 2018 |
| International Cricketers Association | Arts & recreation | 2014 |
| International Machine Tool Group Ltd | Wholesale & retail | 2020 |
| International Maritime Affairs Consultancy Ltd | Professional & scientific | 2022 |
| International Society for Krishna Consciousness Bhaktivedanta Manor Limited | Other services | 2012 |
| International Voice Services Limited | Administrative & support | 2008 |
| Intertechnology Ltd | Information & communication | 2016 |
| Interweb Consulting Limited | Information & communication | 2011 |
| Intouch IS Limited | Professional & scientific | 2012 |
| Intralogistics Aftercare Solutions Limited | Wholesale & retail | 2017 |
| Intu Blockchain Ltd | Professional & scientific | 2018 |
| Inventive Labs Ltd. | Wholesale & retail | 2019 |
| Inventrics Ltd | Information & communication | 2015 |
| Inventum Digital Limited | Administrative & support | 2023 |
| Inventum Finance & Financial Services Limited | Administrative & support | 2010 |
| Inventum Group Limited | Administrative & support | 2005 |
| Inverge Limited | Information & communication | 2004 |
| Invest in Future Limited | Information & communication | 2020 |
| Invest Peak Estate Ltd | Wholesale & retail | 2024 |
| Investigations R US Ltd | Administrative & support | 2012 |
| Investment 246 Limited | Financial services | 2025 |
| Investment Development Ltd | Professional & scientific | 2010 |
| Investnova LG Ltd | Transport & logistics | 2025 |
| Investwise Ltd | Real estate | 2021 |
| Invictus ALC Limited | Wholesale & retail | 2022 |
| Invictus Property Solutions Ltd | Real estate | 2017 |
| Invisio Communications Ltd | Manufacturing | 2004 |
| Invitebase Ltd | Wholesale & retail | 2014 |
| Inwit Properties Limited | Real estate | 2020 |
| IO Energy & Controls Ltd | Construction | 2019 |
| Ionian Technology Limited | Information & communication | 2023 |
| Ionidea Limited | Information & communication | 2007 |
| Ionut Asaftei Ltd | Transport & logistics | 2019 |
| IOS Properties Ltd | Real estate | 2024 |
| Ip-Xchange Limited | Professional & scientific | 1991 |
| Ipeak Global Solutions Limited | Information & communication | 2010 |
| Ipmp Limited | Other services | 2002 |
| IPR Support Systems Ltd | Professional & scientific | 2024 |
| IQ Driving School Ltd | Education | 2021 |
| Iqbal Associates Ltd | Professional & scientific | 2020 |
| Iqbal Halal Meat Ltd | Wholesale & retail | 2019 |
| Iqbal Superstore Ltd | Wholesale & retail | 2021 |
| Iqueg Ltd | Information & communication | 2017 |
| Ir&Ka Ltd | Real estate | 2026 |
| Irbid CP Limited | Financial services | 2024 |
| Iris Chemicals Ltd | Wholesale & retail | 2007 |
| Irock Performance Ltd | Wholesale & retail | 2016 |
| Irongate Property Improvements Ltd | Construction | 2025 |
| Ironstone Asset Management Limited | Real estate | 2021 |
| Irwin Neuropsychology Limited | Health & social care | 2025 |
| Isaroca Architects Ltd | Professional & scientific | 2023 |
| Isbs Limited | Other services | 2006 |
| Isense Illumination UK Limited | Wholesale & retail | 2024 |
| Ishaan Technologies Ltd | Information & communication | 2014 |
| Isight International Ltd | Administrative & support | 2017 |
| Iskcon Foundation Ltd | Education | 2004 |
| Islamic College for Advanced Studies | Professional & scientific | 2010 |
| Island Box Ltd | Hospitality | 2024 |
| ISN Consultancy Ltd | Professional & scientific | 2024 |
| Isobel Perl Limited | Wholesale & retail | 2020 |
| Isodey Ltd | Administrative & support | 2026 |
| Isolutions Management Limited | Real estate | 2010 |
| Ispex Limited | Wholesale & retail | 2009 |
| Israa Tech Ltd | Information & communication | 2017 |
| Israelmusic Ltd | Transport & logistics | 2017 |
| Isrctn | Information & communication | 2005 |
| Issac IT Solutions Ltd | Administrative & support | 2025 |
| Issott Partnership Limited | Construction | 2020 |
| Istic Networks Limited | Professional & scientific | 2010 |
| Isys Solutions Limited | Information & communication | 2014 |
| IT and Actuarial Solutions Ltd | Other services | 2009 |
| IT Devices Ltd | Other services | 2023 |
| IT Project Services Limited | Information & communication | 2011 |
| IT Revival Ltd | Wholesale & retail | 2007 |
| It's About Time Limited | Financial services | 1998 |
| It's Media Productions Ltd | Professional & scientific | 2024 |
| It's UR HQ Ltd | Manufacturing | 2024 |
| It-Me-Up Ltd | Wholesale & retail | 2017 |
| Italian Woodfired Pizza Watford Limited | Hospitality | 2024 |
| Itcm Global Services Limited | Information & communication | 2002 |
| Itech Hub Ltd | Information & communication | 2023 |