| Ideal Supermarket Limited | Wholesale & retail | 2010 |
| IGC Estates Limited | Households | 2010 |
| IGC Rentals Limited | Real estate | 2019 |
| Ignatenka Ltd | Transport & logistics | 2018 |
| Igrock Ltd | Construction | 2021 |
| IJD Motors Limited | Wholesale & retail | 2023 |
| Iliral Ltd | Wholesale & retail | 2021 |
| Iliyan Angelov Ltd | Transport & logistics | 2026 |
| Imcl Accounting Limited | Professional & scientific | 2014 |
| Imperator Investments Limited | Extraterritorial | 1997 |
| Imperial Car Care Limited | Wholesale & retail | 2018 |
| Impressions Event Hire Limited | Hospitality | 2026 |
| IMS Security Products Ltd | Administrative & support | 2014 |
| IN and OUT Fashion Limited | Wholesale & retail | 2024 |
| Independent Animal Clinic Ltd | Professional & scientific | 2023 |
| Independent Grab Company Ltd | Construction | 2019 |
| Indian Cultural Organisation of Lincolnshire Limited | Education | 2022 |
| Indus Health Limited | Health & social care | 2026 |
| Industry Investment Group Limited | Extraterritorial | 1997 |
| Industry Investments Limited | Extraterritorial | 1999 |
| Industry to Industry, Inc. | | 1999 |
| Inetdev Limited | Information & communication | 2000 |
| Infinity Academies Trust | Education | 2013 |
| Infinity HGM Holdings Ltd | Financial services | 2026 |
| Infoexpress Property Ltd | Real estate | 2020 |
| Infoexpress-Boston Limited | Information & communication | 2017 |
| Ingamells Groundworks & Construction Limited | Construction | 2005 |
| Ingleborough Farms Limited | Agriculture & fishing | 2014 |
| Initium Solutions Limited | Construction | 2020 |
| Innovaware Ltd | Information & communication | 2025 |
| Insignia Search Ltd | Administrative & support | 2022 |
| Inspired Ecology Ltd | Professional & scientific | 2012 |
| Inspired Equine Assisted Learning CIC | Health & social care | 2015 |
| Inspiring Lives Ltd | Administrative & support | 2015 |
| Integra Boston Ltd | Professional & scientific | 2024 |
| Integral Mortgages & Protection Limited | Financial services | 2014 |
| Integration Automation Support Ltd | Administrative & support | 2021 |
| Intellitech Services Limited | Public administration | 2017 |
| Intermensa Limited | Professional & scientific | 1976 |
| Intersystems Corporation | | 1986 |
| Invest Limited | Financial services | 2025 |
| Invicta Global Ltd | Health & social care | 2024 |
| Ip&P Limited | Professional & scientific | 2014 |
| Ireland's Farm Machinery Limited | Wholesale & retail | 2002 |
| Irish International Immigrant Center, Inc. | | 2012 |
| Iron Gate Enterprises Ltd | Information & communication | 2025 |
| Ironclad Contracting Services Ltd | Transport & logistics | 2024 |
| Ironclad Contracting Solutions Ltd | Transport & logistics | 2025 |
| Ironele Ltd | Wholesale & retail | 2025 |
| Isaacs Furniture Store Limited | Wholesale & retail | 2013 |
| Iselionis Ltd | Transport & logistics | 2021 |
| Ishgreen Global Limited | Wholesale & retail | 2026 |
| ISO Assist Ltd | Information & communication | 2020 |
| Issico Ltd | Construction | 2013 |
| Istanbul Mildenhall Ltd | Hospitality | 2020 |
| Italian Connection Limited | Hospitality | 2019 |
| Itnc Technologies Ltd | Information & communication | 2012 |
| IU Industries Ltd | Wholesale & retail | 2025 |
| IV Transport Ltd | Transport & logistics | 2026 |
| IVY Crescent Boston Limited | Real estate | 2019 |
| Iweb Limited | Information & communication | 2007 |
| IWL Properties Limited | Real estate | 2016 |
| Izzy Rose Ltd | Manufacturing | 2015 |
| J & J Fuels Boston | Wholesale & retail | 2022 |
| J & W Services (Boston) Ltd | Construction | 2025 |
| J a Lettings and Developments Limited | Real estate | 2019 |
| J Chambers & SON Limited | Real estate | 2017 |
| J D Rolfe Limited | Wholesale & retail | 2020 |
| J F & J Edwards & Sons Unlimited | Agriculture & fishing | 2003 |
| J Hull Wholesale Ltd | Wholesale & retail | 2016 |
| J Isaac Stoves Ltd | Wholesale & retail | 2014 |
| J J Fletcher Financial Ltd | Financial services | 2025 |
| J J Grant 2024 | Financial services | 2024 |
| J J Grant Company | Agriculture & fishing | 1953 |
| J Parker Electrical Ltd | Construction | 2019 |
| J Rapha Medics Limited | Health & social care | 2024 |
| J Rapha Properties Limited | Real estate | 2026 |
| J Stokes Building Contractors Limited | Construction | 2019 |
| J T Waugh Holdings Limited | Financial services | 2026 |
| J T Waugh Management LLP | | 2026 |
| J W Grant Co | Agriculture & fishing | 1954 |
| J&M Rendering and Plastering Specialists Ltd | Construction | 2025 |
| J&N Accounting Services Limited | Professional & scientific | 2016 |
| J. and J. Parsons (London) Limited | Hospitality | 1976 |
| J. Skinner (Building Contractor) Limited | Construction | 2002 |
| J.Art Transport Ltd | Transport & logistics | 2025 |
| J.E.G. Farms Limited | Agriculture & fishing | 1984 |
| J.Em.C Enterprises Limited | Wholesale & retail | 2017 |
| J.K.S. Trans Ltd | Transport & logistics | 2018 |
| J.S.(Farms)Limited | Agriculture & fishing | 1963 |
| J2S Enterprises Ltd | Professional & scientific | 2015 |
| JAA Medical Services Limited | Health & social care | 2013 |
| JAC Air Conditioning Limited | Manufacturing | 2010 |
| Jackdoor Properties Limited | Real estate | 2004 |
| Jackle Ltd | Wholesale & retail | 2025 |
| Jaffna International Ltd | Wholesale & retail | 2026 |
| Jaffna Ltd | Wholesale & retail | 2022 |
| Jagger Homes Limited | Real estate | 1997 |
| Jagstone Ltd | Wholesale & retail | 2010 |
| Jake Brooks Electrical Ltd | Construction | 2021 |