| Inspirational Buildings Ltd | Construction | 2022 |
| Inspired Client Management Limited | Professional & scientific | 2018 |
| Installation AV Limited | Construction | 2013 |
| Instawis Networks Ltd | Information & communication | 2024 |
| Institute of School Business Leadership | Education | 1997 |
| Intastruct Limited | Construction | 1988 |
| Intastruct Raised Flooring Limited | Construction | 1993 |
| Integra Contracting Ltd | Construction | 2026 |
| Integration Consultancy Services Ltd | Information & communication | 2016 |
| Intelagencia Ltd | Information & communication | 2022 |
| Inteligencia Artificial Ltd | Information & communication | 2024 |
| Intelligent PV Limited | Professional & scientific | 2011 |
| Interactive Training Solutions Limited | Education | 2016 |
| Interim Executive Consulting Ltd | Professional & scientific | 2012 |
| Interior Elegance Ltd | Other services | 2013 |
| Interior Elegance Plastering Contractors Limited | Professional & scientific | 2017 |
| Interior Lining Consultancy Ltd | Construction | 2024 |
| International Copper Traders Limited | Wholesale & retail | 2024 |
| International HR Solutions Ltd | Professional & scientific | 2015 |
| International Media (2021) Limited | Information & communication | 2021 |
| International Metals and Cable Recycling Limited | Manufacturing | 2018 |
| International Petroleum Group Limited | Professional & scientific | 2020 |
| International Polymers Limited | Professional & scientific | 2017 |
| Interqo Capital Ltd | Professional & scientific | 2022 |
| Intex Projects Limited | Administrative & support | 2002 |
| Into Shape Agility Ltd | Other services | 2026 |
| INV08 Limited | Financial services | 2021 |
| Investhome Real Estate Ltd | Real estate | 2026 |
| Investor in Students Ltd | Information & communication | 2021 |
| Invigorate Nutrition Ltd | Wholesale & retail | 2025 |
| Invilogix Limited | Information & communication | 2024 |
| Ioana Caluianu Ltd | Manufacturing | 2026 |
| Iobuy Ltd | Professional & scientific | 2021 |
| IP - Smart Ltd | Professional & scientific | 2021 |
| Ipsimus Ltd | Information & communication | 2014 |
| Iqpark Ltd | Wholesale & retail | 2020 |
| Ireland Associates Limited | Professional & scientific | 2015 |
| Iris Ignis Group Ltd | Financial services | 2024 |
| Iris Photography Ltd | Professional & scientific | 2024 |
| Iron and Glass Limited | Manufacturing | 2026 |
| Isar Limited | Administrative & support | 2000 |
| Isat (Training) Ltd | Health & social care | 2013 |
| Isbl Trading Limited | Education | 2017 |
| Islington Pianos Ltd | Arts & recreation | 2018 |
| ISN Homes Ltd | Real estate | 2024 |
| Isnc Medical Limited | Health & social care | 2016 |
| Isogym Ltd | Financial services | 2023 |
| ITA Design Surfacing Limited | Professional & scientific | 2021 |
| Itech-Design Ltd | Information & communication | 2008 |
| Ivahouse Ltd | Real estate | 2000 |
| Ivolo Ltd | Education | 2010 |
| Ivory Hospitality Services Ltd | Administrative & support | 2018 |
| Iwaniszyn Ltd | Transport & logistics | 2018 |
| J & B Homes Ltd | Real estate | 2020 |
| J & C Peake Contracts Limited | Construction | 2017 |
| J & J Design Studio Limited | Professional & scientific | 2015 |
| J & K Gastech Limited | Construction | 2012 |
| J & K Gastech Maintenance Ltd | Construction | 2013 |
| J & M Kibirige Limited | Real estate | 2021 |
| J & SS Investments Limited | Real estate | 2023 |
| J Concepts Ltd | Real estate | 2023 |
| J D Eight Limited | Hospitality | 2019 |
| J H Fitness Bidford Ltd | Arts & recreation | 2019 |
| J Jones Assets Ltd | Real estate | 2025 |
| J K Smith & Sons Ltd | Agriculture & fishing | 2026 |
| J Khan Writing Ltd | Wholesale & retail | 2023 |
| J M Smith Property Limited | Real estate | 2021 |
| J S Kang Limited | Professional & scientific | 2004 |
| J S Padel Limited | Arts & recreation | 2026 |
| J S Trade Properties Limited | Construction | 2018 |
| J Sandher Ltd | Hospitality | 2022 |
| J Shokar Consultancy Limited | Extraterritorial | 2011 |
| J Thompson Building Contractor (Midlands) Limited | Construction | 2021 |
| J&C Property Collection Limited | Real estate | 2024 |
| J&J Brands Ltd | Wholesale & retail | 2026 |
| J. C. Builders (Leamington) Limited | Construction | 2019 |
| J. M. Morris Plant Hire Ltd | Administrative & support | 2014 |
| J.B Construction (Warwickshire) Limited | Construction | 2016 |
| J.H.Gibb(Melrose)Limited | Financial services | 1965 |
| J.M Morris Holdings Ltd | Financial services | 2022 |
| J.P. DHS Ltd | Health & social care | 2018 |
| J.P.Obrien Ltd | Agriculture & fishing | 2017 |
| J.P.S. (2014) Ltd | Construction | 2015 |
| J.R.B.T. Limited | Professional & scientific | 2014 |
| J.R.S. Oaks Corner (Management) Limited | Households | 2001 |
| J0927 Ltd | Information & communication | 2025 |
| Jabit Limited | Professional & scientific | 2012 |
| Jacc Leamington Limited | Real estate | 2023 |
| Jack Coots-Williams Ltd | Wholesale & retail | 2023 |
| Jackie Ball Films Limited | Information & communication | 2018 |
| Jacklily Home Care Ltd | Administrative & support | 2021 |
| Jackray Ltd | Professional & scientific | 2020 |
| Jacoby Rugs Ltd | Wholesale & retail | 2016 |
| Jadb Investments Ltd | Real estate | 2020 |
| Jadb Trading Ltd | Households | 2021 |
| Jade Lettings Limited | Real estate | 2013 |
| Jahama Investments 1 Ltd | Financial services | 2025 |
| Jahama Limited | Financial services | 2017 |
| Jahama Properties UK Limited | Real estate | 2019 |
| Jakob Wright Vehicle Tech Ltd | Wholesale & retail | 2023 |