| Imas Aquatic Services Limited | Professional & scientific | 2013 |
| IMF Audit Ltd | Professional & scientific | 2013 |
| IMF Direct Limited | Wholesale & retail | 2013 |
| Immersibility Ltd | Arts & recreation | 2025 |
| Immobiliare Commercial Limited | Real estate | 2018 |
| Immobiliare Investments Limited | Real estate | 2017 |
| Immobiliare Trading Limited | Other services | 2019 |
| Imogen Jones Recruitment Limited | Administrative & support | 2019 |
| Impact Personal Training Limited | Arts & recreation | 2014 |
| Impact Surveys Limited | Wholesale & retail | 2009 |
| Impera Conservation Limited | Construction | 2024 |
| IMS Rentals and Sales Limited | Real estate | 2021 |
| IN Herts Motors Ltd | Wholesale & retail | 2019 |
| Incatronix Limited | Financial services | 2011 |
| Incatronix Properties Limited | Administrative & support | 2012 |
| Inclusioneering Limited | Professional & scientific | 2021 |
| Inclusive Tuition Limited | Education | 2025 |
| Indastep Ltd | Real estate | 2017 |
| Independent BMW Limited | Wholesale & retail | 2000 |
| Independent DOC Management Ltd | Administrative & support | 2004 |
| Independent Drilling Contractors Limited | Manufacturing | 2021 |
| Indigo Scientific Limited | Professional & scientific | 2002 |
| Indujay Medical Services Limited | Health & social care | 2022 |
| Indus Properties Ltd | Real estate | 2023 |
| Industrial Air Conditioning Limited | Construction | 1967 |
| Industrial Belting International Limited | Manufacturing | 2000 |
| Infinity Proserv Ltd | Construction | 2020 |
| Infocus Moments Limited | Professional & scientific | 2024 |
| Information Technologies Limited | Information & communication | 2012 |
| Infrastructure Planning Services Ltd | Professional & scientific | 2023 |
| Infusion Wellbeing Limited | Other services | 2022 |
| Ingledown Limited | Real estate | 1998 |
| Inground Utilities Limited | Construction | 2011 |
| Initio Homes Ltd | Real estate | 2013 |
| Inncheck Limited | Administrative & support | 2015 |
| Innernutshell Ltd | Real estate | 2021 |
| Innogise Ltd | Information & communication | 2012 |
| Innovated Limited | Information & communication | 2011 |
| Inqlabs Ltd | Professional & scientific | 2022 |
| Insight Narrator Limited | Professional & scientific | 2012 |
| Insight-Iq Ltd | Administrative & support | 2014 |
| Inspire by JEM Ltd | Professional & scientific | 2023 |
| Instinctive Communications Limited | Professional & scientific | 2023 |
| Instrumel Ltd | Professional & scientific | 1997 |
| Intatest Limited | Information & communication | 2016 |
| Integrated Facilities Systems Limited | Administrative & support | 2002 |
| Integrius Ltd | Information & communication | 2026 |
| Intelligreen Innovations Ltd | Extraterritorial | 2013 |
| Inter Partes Limited | Professional & scientific | 2013 |
| Interactive Agents Limited | Arts & recreation | 2017 |
| Interco Services Ltd | Wholesale & retail | 2018 |
| Intermonitor Limited | Wholesale & retail | 1996 |
| International Academy for Professional Development Limited | Education | 2010 |
| International Music Artists Rights Alliance Ltd | Information & communication | 2025 |
| International Science Writer Ltd | Administrative & support | 2009 |
| International Society for Coaching Psychology | Other services | 2008 |
| International Techmedia Ltd | Information & communication | 2013 |
| Internet 4U Ltd | Information & communication | 2005 |
| Interstuff Ltd | Information & communication | 2018 |
| Inthink Limited | Information & communication | 2010 |
| Inua Design Ltd | Extraterritorial | 2014 |
| Invested Recruiter Group Ltd | Professional & scientific | 2020 |
| Investmore Ltd | Real estate | 2012 |
| Invetex Limited | Professional & scientific | 2024 |
| Iona Lettings Limited | Real estate | 2026 |
| Iona Property Solutions Ltd | Real estate | 2014 |
| Iqon Limited | Administrative & support | 1998 |
| IRD Homes (London) Limited | Real estate | 2006 |
| Irene's Ghost Ltd | Information & communication | 2015 |
| IS Civils Ltd | Construction | 2025 |
| Isabelle Estates Ltd | Real estate | 2011 |
| Islajack Limited | Other services | 2024 |
| Island Decking Limited | Administrative & support | 2021 |
| Isometric Ltd | Information & communication | 2021 |
| Istructure Engineering & Consultancy Services Limited | Professional & scientific | 2017 |
| IT Consultancy Solutions Ltd | Information & communication | 2023 |
| Itkas Co Limited | Construction | 2013 |
| ITW27 Ltd | Arts & recreation | 2026 |
| Ivashawnic ENG Solutions Ltd | Professional & scientific | 2026 |
| Ivel Construction Limited | | 1987 |
| Ivel Precision Engineering Limited | Manufacturing | 1998 |
| Ivelbrook Limited | Real estate | 2016 |
| Ivorproperty Ltd | Real estate | 2026 |
| IVY & Co UK Ltd | Wholesale & retail | 2021 |
| IWAX3D Ltd | Wholesale & retail | 2019 |
| J & S Oakley Limited | Agriculture & fishing | 2021 |
| J B Circuits Limited | Administrative & support | 1987 |
| J Boot Ltd | Professional & scientific | 2025 |
| J Burden Property Ltd | Real estate | 2024 |
| J Buthee Limited | Real estate | 2019 |
| J C Agriculture Limited | Agriculture & fishing | 2012 |
| J D Heating & Plumbing Services Limited | Construction | 2015 |
| J E Richford Limited | Manufacturing | 2025 |
| J G Woodwork Limited | Construction | 2018 |
| J Georgeson Fitness Limited | Other services | 2019 |
| J Hare & Sons Ltd | Construction | 2013 |
| J Hare Diamond Drilling (Hitchin) Limited | Construction | 1999 |
| J Nutley Estates Limited | Real estate | 2022 |
| J R Roofing Services Limited | Extraterritorial | 2021 |
| J&D MAC Brothers Limited | Other services | 2023 |