| Invitation CRM Ltd | Construction | 2019 |
| Inviting Minds Ltd | Information & communication | 2025 |
| Ioncycle Ltd | Professional & scientific | 2022 |
| Ionics (U.K.) Limited | Professional & scientific | 1985 |
| Ionics Ventures Limited | Professional & scientific | 2001 |
| Ionserve Ltd | Professional & scientific | 2025 |
| Iovance Biotherapeutics UK Ltd | Manufacturing | 2023 |
| Iovance Biotherapeutics UK SP Ltd | Wholesale & retail | 2013 |
| Ipct Consulting Limited | Administrative & support | 2022 |
| Iplogix Ltd | Information & communication | 2014 |
| Ipsa Solutions Limited | Information & communication | 2017 |
| IQ Diabetes Limited | Health & social care | 2013 |
| Iqraa Ltd | Education | 2025 |
| IRE Systems Consultancy Ltd | Information & communication | 2019 |
| IRE Systems Ltd | Information & communication | 2013 |
| Irewardhealth UK Ltd | Information & communication | 2016 |
| Irida Advisors Limited | Professional & scientific | 2021 |
| Iron Butterfly Ltd | Arts & recreation | 2007 |
| Iron Butterfly Properties Ltd | Real estate | 2016 |
| Ironclad Software Consulting Ltd | Information & communication | 2022 |
| Ironfocus Consulting Limited | Professional & scientific | 2024 |
| Ironhill Limited | Professional & scientific | 2003 |
| Ironshore Global Investors Ltd | Professional & scientific | 2010 |
| Irwell Care Services Ltd | Health & social care | 2018 |
| Irwin Place Management Company Limited | Households | 2001 |
| Isabellita Bakes Ltd | Manufacturing | 2021 |
| Isao Hunters Limited | Information & communication | 2018 |
| Isara Laboratories UK Ltd | Information & communication | 2025 |
| Isca Photonics Limited | Information & communication | 2007 |
| Isdb Limited | Professional & scientific | 2025 |
| Isha Keymist Associates Ltd | Professional & scientific | 2014 |
| Ishpran Limited | Health & social care | 2026 |
| Isirame Omenai Limited | Construction | 2011 |
| Isla Therapy and Consulting Ltd | Health & social care | 2023 |
| Island Ventures Limited | Professional & scientific | 2016 |
| ISM Medical Ltd | Health & social care | 2012 |
| Isora Consulting Limited | Professional & scientific | 2012 |
| ISR Medical Ltd | Health & social care | 2016 |
| Israa Investments Limited | Administrative & support | 2008 |
| Istd HR Development (UK) C.I.C. | Administrative & support | 2025 |
| Istdp-North Ltd | Health & social care | 2020 |
| IT and ERP Limited | Information & communication | 2019 |
| IT and MOR Consulting Limited | Professional & scientific | 2017 |
| IT BI Consulting Limited | Information & communication | 2018 |
| IT Galaxy Limited | Information & communication | 2024 |
| IT Procurement Advisory Services Limited | Professional & scientific | 2024 |
| IT Services Manchester Ltd | Information & communication | 2002 |
| IT Sun Solutions Limited | Information & communication | 2011 |
| It's NOW Live! Limited | Information & communication | 2012 |
| ITA Group Holdings Limited | Financial services | 2024 |
| Itaflon UK Limited | Manufacturing | 2023 |
| Italian Classic Cars Limited | Wholesale & retail | 2015 |
| Italian Larder Limited | Wholesale & retail | 2025 |
| Itarck Limited | Professional & scientific | 2020 |
| ITC Properties Limited | Administrative & support | 2004 |
| Itcrux Services Ltd | Information & communication | 2010 |
| ITERATE2INNOVATE Limited | Professional & scientific | 2017 |
| Ithaka Property Ltd | Real estate | 2022 |
| Itizan Coaching Limited | Health & social care | 2026 |
| Itsm Snow Solutions Limited | Information & communication | 2017 |
| Ittela Limited | Information & communication | 2025 |
| Ivanhoe Freehold Limited | Households | 2023 |
| Ivaorg CIC | Financial services | 2013 |
| Ivaorg Insolvency Limited | Extraterritorial | 2015 |
| Ivision Technology Limited | Wholesale & retail | 2019 |
| IVY and Bloom Limited | Health & social care | 2025 |
| IVY Domiciliary Care Ltd | Health & social care | 2026 |
| IVY Grey Interiors Limited | Wholesale & retail | 2019 |
| IVY House (Merrymans) Limited | Households | 2003 |
| IVY House Productions Limited | Administrative & support | 2016 |
| IVY LOU Consulting Limited | Professional & scientific | 2019 |
| IVY Rose Birch Holdings Limited | Financial services | 2026 |
| Ivyleague (UK) Limited | Wholesale & retail | 2002 |
| Iwan Property Development Limited | Real estate | 2020 |
| IWM Group Limited | Financial services | 2023 |
| Izzy Grace Limited | Financial services | 2025 |
| J & a Medic Ltd | Health & social care | 2025 |
| J & B Autos Limited | Wholesale & retail | 2015 |
| J & G Marshall Limited | Administrative & support | 2009 |
| J & K Bushell Ltd | Agriculture & fishing | 2025 |
| J & R Hutchins - Landmac | | 2006 |
| J & T LEE Property Consultants Limited | Real estate | 2021 |
| J and a Home Interiors Ltd | Wholesale & retail | 2025 |
| J Barnes Consultancy Ltd | Professional & scientific | 2016 |
| J Brooks PT Limited | Education | 2025 |
| J Bryl Limited | Professional & scientific | 2025 |
| J C Swithenbank Limited | Professional & scientific | 2024 |
| J D D C Mcgoff LLP | | 2011 |
| J Deveer Ltd | Manufacturing | 2020 |
| J E Property Maintenance Ltd | Construction | 2008 |
| J G Woolfe Civil Engineering Limited | Construction | 2016 |
| J Heath Medical Limited | Health & social care | 2024 |
| J J Bigman Investment Limited | Real estate | 2020 |
| J Kelly Property Limited | Real estate | 2023 |
| J Living Ltd | Real estate | 2025 |
| J Lord & Co (Cheshire) Limited | Real estate | 2003 |
| J M Heaford Limited | Manufacturing | 1982 |
| J Mendoza Limited | Professional & scientific | 2026 |
| J Nickson & Sons Limited | Real estate | 2025 |
| J R Norris Limited | Professional & scientific | 2023 |